- Finding Feature Information
- Contents
- Information About Configuring IP Routing Protocol-Independent Features
- How to Configure IP Routing Protocol-Independent Features
- Example: Variable-Length Subnet Mask
- Example: Overriding Static Routes with Dynamic Protocols
- Example: Administrative Distances
- Example: Static Routing Redistribution
- Example: EIGRP Redistribution
- Example: Simple Redistribution
- Example: Complex Redistribution
- Examples: OSPF Routing and Route Redistribution
- Example: Default Metric Values Redistribution
- Example: Route Map
- Example: Passive Interface
- Example: Policy-Based Routing
- Example: Policy Routing with CEF
- Examples: QoS Policy Propagation via BGP Configuration
- Examples: Key Management
Configuring IP Routing Protocol-Independent Features
The Configuring IP Routing Protocol-Independent Features module describes how to configure IP routing protocol-independent features. For a complete description of the IP routing protocol-independent commands in this chapter, see the Cisco IOS IP Routing: Protocol-Independent Command Reference. To locate documentation of other commands in this chapter, use the command reference master index or search online.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Configuring IP Routing Protocol-Independent Features" section.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
•
Information About Configuring IP Routing Protocol-Independent Features
•How to Configure IP Routing Protocol-Independent Features
•Configuration Examples for Configuring IP Routing Protocol-Independent Features
•Feature Information for Configuring IP Routing Protocol-Independent Features
Information About Configuring IP Routing Protocol-Independent Features
To configure optional protocol-independent features, perform any of the tasks described in the following sections.
•Multi-Interface Load Splitting
•Routing Information Redistribution
•Sources of Routing Information Filtering
•Authentication Keys Management
Variable-Length Subnet Masks
Enhanced Interior Gateway Routing Protocol (EIGRP), Intermediate System-to-Intermediate System (IS-IS), Open Shortest Path First (OSPF), Routing Information Protocol (RIP) Version 2, and static routes support variable-length subnet masks (VLSMs). With VLSMs, you can use different masks for the same network number on different interfaces, which allows you to conserve IP addresses and more efficiently use available address space. However, using VLSMs also presents address assignment challenges for the network administrator and ongoing administrative challenges.
Refer to RFC 1219 for detailed information about VLSMs and how to correctly assign addresses.
Note Consider your decision to use VLSMs carefully. You can easily make mistakes in address assignments and you will generally find it more difficult to monitor your network using VLSMs.
Note The best way to implement VLSMs is to keep your existing addressing plan in place and gradually migrate some networks to VLSMs to recover address space. See the "Example: Variable-Length Subnet Mask" section for an example of using VLSMs.
Static Routes
Static routes are user-defined routes that cause packets moving between a source and a destination to take a specified path. Static routes can be important if the router cannot build a route to a particular destination. They are also useful for specifying a gateway of last resort to which all unroutable packets will be sent.
To configure a static route, use the ip route prefix mask {ip-address | interface-type interface-number [ip-address]} [distance] [name] [permanent | track number] [tag tag] command in global configuration mode.
See the "Example: Overriding Static Routes with Dynamic Protocols" section for an example of configuring static routes.
Static routes remains in the router configuration until you remove them (using the no form of the ip route global configuration command). However, you can override static routes with dynamic routing information through prudent assignment of administrative distance values. Each dynamic routing protocol has a default administrative distance, as listed in Table 1. If you would like a static route to be overridden by information from a dynamic routing protocol, simply ensure that the administrative distance of the static route is higher than that of the dynamic protocol.
Static routes that point to an interface will be advertised via RIP, EIGRP, and other dynamic routing protocols, regardless of whether redistribute static router configuration commands were specified for those routing protocols. These static routes are advertised because static routes that point to an interface are considered in the routing table to be connected and hence lose their static nature. However, if you define a static route to an interface that is not one of the networks defined in a network command, no dynamic routing protocols will advertise the route unless a redistribute static command is specified for these protocols.
When an interface goes down, all static routes through that interface are removed from the IP routing table. Also, when the software can no longer find a valid next hop for the address specified as the address of the forwarding router in a static route, the static route is removed from the IP routing table.
Default Routes
A router might not be able to determine the routes to all other networks. To provide complete routing capability, the common practice is to use some routers as smart routers and give the remaining routers default routes to the smart router. (Smart routers have routing table information for the entire internetwork.) These default routes can be passed along dynamically, or can be configured into the individual routers.
Most dynamic interior routing protocols include a mechanism for causing a smart router to generate dynamic default information that is then passed along to other routers.
Default Network
If a router has a directly connected interface onto the specified default network, the dynamic routing protocols running on that device will generate or source a default route. In the case of RIP, the router will advertise the pseudonetwork 0.0.0.0. In the case of EIGRP, the network itself is advertised and flagged as an external route.
A router that is generating the default for a network also may need a default of its own. One way a router can generate its own default is to specify a static route to the network 0.0.0.0 through the appropriate device.
To define a static route to a network as the static default route, use the ip default-network network-number command in global configuration mode.
Gateway of Last Resort
When default information is being passed along through a dynamic routing protocol, no further configuration is required. The system periodically scans its routing table to choose the optimal default network as its default route. In the case of RIP, there is only one choice, network 0.0.0.0. In the case of EIGRP, there might be several networks that can be candidates for the system default. Cisco IOS software uses both administrative distance and metric information to determine the default route (gateway of last resort). The selected default route appears in the gateway of last resort display of the show ip route EXEC command.
If dynamic default information is not being passed to the software, candidates for the default route are specified with the ip default-network global configuration command. In this usage, the ip default-network command takes an unconnected network as an argument. If this network appears in the routing table from any source (dynamic or static), it is flagged as a candidate default route and is a possible choice as the default route.
If the router has no interface on the default network, but does have a route to it, it considers this network as a candidate default path. The route candidates are examined and the best one is chosen, based on administrative distance and metric. The gateway to the best default path becomes the gateway of last resort.
Maximum Number of Paths
By default, most IP routing protocols install a maximum of four parallel routes in a routing table. Static routes always install six routes. The exception is BGP, which by default allows only one path (the best path) to a destination. However, BGP can be configured to use equal and unequal cost multipath load sharing. See the "BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN" feature of the Cisco IOS IP Routing: BGP Configuration Guide for more information.
The number of parallel routes that you can configure to be installed in the routing table is dependent on the installed version of Cisco IOS software. To change the maximum number of parallel paths allowed, use the maximum-paths number-paths command in router configuration mode.
Multi-Interface Load Splitting
Multi-interface load splitting allows you to efficiently control traffic that travels across multiple interfaces to the same destination. The traffic-share min router configuration command specifies that if multiple paths are available to the same destination, only paths with the minimum metric will be installed in the routing table. The number of paths allowed is never more than six. For dynamic routing protocols, the number of paths is controlled by the maximum-paths router configuration command. The static route source can always install six paths. If more paths are available, the extra paths are discarded. If some installed paths are removed from the routing table, pending routes are added automatically.
When the traffic-share min command is used with the across-interfaces keyword, an attempt is made to use as many different interfaces as possible to forward traffic to the same destination. When the maximum path limit has been reached and a new path is installed, the router compares the installed paths. For example, if path X references the same interface as path Y and the new path uses a different interface, path X is removed and the new path is installed.
To configure traffic that is distributed among multiple routes of unequal cost for equal cost paths across multiple interfaces, use the traffic-share min across-interfaces command in router configuration mode.
Routing Information Redistribution
In addition to running multiple routing protocols simultaneously, Cisco IOS software can be configured to redistribute information from one routing protocol to another. For example, you can configure a router to readvertise EIGRP-derived routes using RIP, or to readvertise static routes using the EIGRP protocol. Redistribution from one routing protocol to another can be configured in all of the IP-based routing protocols.
You also can conditionally control the redistribution of routes between routing domains by configuring route maps between the two domains. A route map is a route/ packet filter that is configured with permit and deny statements, match and set clauses, and sequence numbers.
The following four tables list tasks associated with route redistribution. Although redistribution is a protocol-independent feature, some of the match and set commands are specific to a particular protocol.
To define a route map for redistribution, use the route-map map-tag [permit | deny] [sequence-number] command in global configuration mode.
One or more match commands and one or more set commands are configured in route map configuration mode. If there are no match commands, then everything matches. If there are no set commands, then no set action is performed.
To define conditions for redistributing routes from one routing protocol into another, see the "Configuring Redistribution Routing Information" section
See the Connecting to a Service Provider Using External BGP module of the Cisco IOS IP Routing: BGP Configuration Guide for examples of BGP route map configuration tasks and configuration examples. See the Configuring BGP Cost Community feature Cisco IOS IP Routing: BGP Configuration Guide for examples of BGP communities and route maps.
The metrics of one routing protocol do not necessarily translate into the metrics of another. For example, the RIP metric is a hop count and the EIGRP metric is a combination of five metric values. In such situations, a dynamic metric is assigned to the redistributed route. Redistribution in these cases should be applied consistently and carefully in conjunction with inbound filtering to avoid routing loops.
Removing options that you have configured for the redistribute command requires careful use of the no form of the redistribute command to ensure that you obtain the result that you are expecting.
Supported Metric Translations
This section describes supported automatic metric translations between the routing protocols. The following descriptions assume that you have not defined a default redistribution metric that replaces metric conversions:
•RIP can automatically redistribute static routes. It assigns static routes a metric of 1 (directly connected).
•BGP does not normally send metrics in its routing updates.
•EIGRP can automatically redistribute static routes from other EIGRP-routed autonomous systems as long as the static route and any associated interfaces are covered by an EIGRP network statement. EIGRP assigns static routes a metric that identifies them as directly connected. EIGRP does not change the metrics of routes derived from EIGRP updates from other autonomous systems.
Note Any protocol can redistribute routes from other routing protocols as long as a default metric is configured.
Default Passive Interfaces
In Internet service provider (ISP) and large enterprise networks, many of the distribution routers have more than 200 interfaces. Before the introduction of the Default Passive Interface feature, there were two possibilities for obtaining routing information from these interfaces:
•Configure a routing protocol such as OSPF on the backbone interfaces and redistribute connected interfaces.
•Configure the routing protocol on all interfaces and manually set most of them as passive.
Network operators may not always be able to summarize type 5 link-state advertisements (LSAs) at the router level where redistribution occurs, as in the first possibility. Thus, a large number of type 5 LSAs can be flooded over the domain.
In the second possibility, large type 1 LSAs might be flooded into the area. The Area Border Router (ABR) creates type 3 LSAs, one for each type 1 LSA, and floods them to the backbone. It is possible, however, to have unique summarization at the ABR level, which will inject only one summary route into the backbone, thereby reducing processing overhead.
The prior solution to this problem was to configure the routing protocol on all interfaces and manually set the passive-interface router configuration command on the interfaces where adjacency was not desired. But in some networks, this solution meant coding 200 or more passive interface statements. With the Default Passive Interface feature, this problem is solved by allowing all interfaces to be set as passive by default using a single passive-interface default command, then configuring individual interfaces where adjacencies are desired using the no passive-interface command.
Thus, the Default Passive Interface feature simplifies the configuration of distribution routers and allows the network manager to obtain routing information from the interfaces in large ISP and enterprise networks.
To set all interfaces as passive by default and then activate only those interfaces that must have adjacencies set, see the "Configuring Default Passive Interfaces" section.
Sources of Routing Information Filtering
Filtering sources of routing information prioritizes routing information from different sources because some pieces of routing information may be more accurate than others. An administrative distance is a rating of the trustworthiness of a routing information source, such as an individual router or a group of routers. In a large network, some routing protocols and some routers can be more reliable than others as sources of routing information. Also, when multiple routing processes are running in the same router for IP, it is possible for the same route to be advertised by more than one routing process. By specifying administrative distance values, you enable the router to intelligently discriminate between sources of routing information. The router will always pick the route whose routing protocol has the lowest administrative distance.
To filter sources of routing information, see the "Filtering Sources of Routing Information" section.
There are no general guidelines for assigning administrative distances because each network has its own requirements. You must determine a reasonable matrix of administrative distances for the network as a whole. Table 1 shows the default administrative distance for various routing information sources.
For example, consider a router using EIGRP and RIP. Suppose you trust the EIGRP-derived routing information more than the RIP-derived routing information. In this example, because the default EIGRP administrative distance is lower than the default RIP administrative distance, the router uses the EIGRP-derived information and ignores the RIP-derived information. However, if you lose the source of the EIGRP-derived information (because of a power shutdown at the source network, for example), the router uses the RIP-derived information until the EIGRP-derived information reappears.
For an example of filtering on sources of routing information, see the section "Example: Administrative Distances" section.
Note You can also use administrative distance to rate the routing information from routers that are running the same routing protocol. This application is generally discouraged if you are unfamiliar with this particular use of administrative distance, because it can result in inconsistent routing information, including forwarding loops.
Note The weight of a route can no longer be set with the distance command. To set the weight for a route, use a route map.
Policy-Based Routing
Policy-based routing is a more flexible mechanism for routing packets than destination routing. It is a process whereby the router puts packets through a route map before routing them. The route map determines which packets are routed to which router next. You might enable policy-based routing if you want certain packets to be routed some way other than the obvious shortest path. Possible applications for policy-based routing are to provide equal access, protocol-sensitive routing, source-sensitive routing, routing based on interactive versus batch traffic, and routing based on dedicated links.
To enable policy-based routing, you must identify which route map to use for policy-based routing and create the route map. The route map itself specifies the match criteria and the resulting action if all of the match clauses are met. These steps are described in the following task tables.
To enable policy-based routing on an interface, indicate which route map the router should use by using the following command in interface configuration mode. A packet arriving on the specified interface will be subject to policy-based routing except when its destination IP address is the same as the IP address of the router's interface. To disable fast switching of all packets arriving on this interface use the ip policy route-map map-tag command in interface configuration mode.
To define the route map to be used for policy-based routing, use the route-map map-tag [permit | deny] [sequence-number] command in global configuration mode.
To define the criteria by which packets are examined to learn if they will be policy-based routed, use either match length minimum-length maximum-length command or match ip address {access-list-number | access-list-name} [access-list-number | access-list-name] command or both in route map configuration mode. No match clause in the route map indicates all packets.
To set the precedence and specify where the packets that pass the match criteria are output, see "Configuring precedence for policy-based routed packets" section.
The precedence setting in the IP header determines whether, during times of high traffic, the packets will be treated with more or less precedence than other packets. By default, the Cisco IOS software leaves this value untouched; the header remains with the precedence value that it had.
The precedence bits in the IP header can be set in the router when policy-based routing is enabled. When the packets containing those headers arrive at another router, the packets are ordered for transmission according to the precedence set, if the queueing feature is enabled. The router does not honor the precedence bits if queueing is not enabled; the packets are sent in FIFO order.
You can change the precedence setting, using either a number or name. The names came from RFC 791, but are evolving. You can enable other features that use the values in the set ip precedence route map configuration command to determine precedence. Table 2 lists the possible numbers and their corresponding name, from least important to most important.
|
|
|
|---|---|
0 |
routine |
1 |
priority |
2 |
immediate |
3 |
flash |
4 |
flash-override |
5 |
critical |
6 |
internet |
7 |
network |
The set commands can be used with each other. They are evaluated in the order shown in the previous task table. A usable next hop implies an interface. Once the local router finds a next hop and a usable interface, it routes the packet.
To display the cache entries in the policy route cache, use the show ip cache policy command.
For information about setting the precedence and specifying where the packets that pass the match the criteria for policy-based routing are output, see the "Configuring precedence for policy-based routed packets" section.
For information about configure QoS Policy Propagation via BGP, see the "Configuring QoS Policy Propagation via BGP" section.
See the "Example: Policy-Based Routing" section for an example of policy routing.
Fast-Switched Policy Routing
IP policy routing can also be fast switched. Prior to fast-switched policy routing, policy routing could only be process switched, which meant that on most platforms, the switching rate was approximately 1000 to 10,000 packets per second. Such rates were not fast enough for many applications. Users that need policy routing to occur at faster speeds can now implement policy routing without slowing down the router.
Fast-switched policy routing supports all of the match commands and most of the set commands, except for the following restrictions:
•The set ip default command is not supported.
•The set interface command is supported only over point-to-point links, unless a route cache entry exists using the same interface specified in the set interface command in the route map. Also, at the process level, the routing table is consulted to determine if the interface is on a reasonable path to the destination. During fast switching, the software does not make this check. Instead, if the packet matches, the software blindly forwards the packet to the specified interface.
Policy routing must be configured before you configure fast-switched policy routing. Fast switching of policy routing is disabled by default. To have policy routing be fast switched, use the ip route-cache policy command in interface configuration mode.
Local Policy Routing
Packets that are generated by the router are not normally policy-routed. To enable local policy routing for such packets, indicate which route map the router should use by using the following command in global configuration mode. All packets originating on the router will then be subject to local policy routing. To identify the route map to use for local policy routing, use the ip local policy route-map map-tag command in global configuration mode.
Use the show ip local policy command to display the route map used for local policy routing, if one exists.
NetFlow Policy Routing
NetFlow policy routing (NPR) integrates policy routing, which enables traffic engineering and traffic classification, with NetFlow services, which provide billing, capacity planning, and monitoring information on real-time traffic flows. IP policy routing now works with Cisco Express Forwarding (CEF), distributed CEF (dCEF), and NetFlow.
As quality of service (QoS) and traffic engineering become more popular, so does interest in the ability of policy routing to selectively set IP Precedence and type of service (ToS) bits (based on access lists and packet size), thereby routing packets based on predefined policy. It is important that policy routing work well in large, dynamic routing environments. Hence, distributed support allows customers to leverage their investment in distributed architecture.
NetFlow policy routing leverages the following technologies:
•CEF, which looks at a Forwarding Information Base (FIB) instead of a routing table when switching packets, to address maintenance problems of a demand caching scheme.
•dCEF, which addresses the scalability and maintenance problems of a demand caching scheme.
•NetFlow, which provides accounting, capacity planning, and traffic monitoring capabilities.
Following are NPR benefits:
•NPR takes advantage of the new switching services. CEF, dCEF, and NetFlow can now use policy routing.
•Now that policy routing is integrated into CEF, policy routing can be deployed on a wide scale and on high-speed interfaces.
Following are NPR restrictions:
•NPR is only available on Cisco IOS platforms that support CEF.
•Distributed FIB-based policy routing is only available on platforms that support dCEF.
•The set ip next-hop verify-availability command is not supported in dCEF because dCEF does not support the Cisco Discovery Protocol (CDP) database.
In order for NetFlow policy routing to work, the following features must already be configured:
•CEF, dCEF, or NetFlow
•Policy routing
To configure CEF, or dCEF, refer to the "Cisco Express Forwarding Overview" chapter of the Cisco IOS IP Switching Configuration Guide. To configure NetFlow, refer to the "Cisco IOS NetFlow Overview" chapter of the Cisco IOS NetFlow Configuration Guide.
NPR is the default policy routing mode. No additional configuration tasks are required to enable policy routing in conjunction with CEF, dCEF, or NetFlow. As soon as one of these features is turned on, packets are automatically subject to policy routing in the appropriate switching path.
There is one new, optional configuration command (set ip next-hop verify-availability). This command has the following restrictions:
•It can cause some performance degradation due to CDP database lookup overhead per packet.
•CDP must be enabled on the interface.
•The directly connected next hop must be a Cisco device with CDP enabled.
•The command will not work with dCEF configurations, due to the dependency of the CDP neighbor database.
It is assumed that policy routing itself is already configured.
If the router is policy routing packets to the next hop and the next hop happens to be down, the router will try unsuccessfully to use Address Resolution Protocol (ARP) for the next hop (which is down). This behavior can continue indefinitely.
To prevent this situation from occurring, you can configure the router to first verify that the next hop, using a route map, are CDP neighbors of the router before routing to that next hop.
This task is optional because some media or encapsulations do not support CDP, or it may not be a Cisco device that is sending the router traffic.
To configure the router to verify that the next hop is a CDP neighbor before the router tries to policy-route to it, use the set ip next-hop verify-availability command in route map configuration mode.
If the command shown is set and the next hop is not a CDP neighbor, the router looks to the subsequent next hop, if there is one. If there is none, the packets are simply not policy-routed.
If the command shown is not set, the packets are either policy-routed or remain forever unrouted.
If you want to selectively verify availability of only some next hops, you can configure different route-map entries (under the same route-map name) with different criteria (using access list matching or packet size matching), and use the set ip next-hop verify-availability configuration command selectively.
Typically, you would use existing policy routing and NetFlow show commands to monitor these features. For more information on these show commands, refer to the Cisco IOS IP Routing: Protocol Independent Command Reference for policy routing commands and the appropriate chapter of the Cisco IOS IP NetFlow Command Reference for NetFlow commands.
To display the route-map Inter Processor Communication (IPC) message statistics in the Route Processor (RP) or Versatile Interface Processor (VIP), use the show route-map ipc command in EXEC mode.
Authentication Keys Management
Key management is a method of controlling authentication keys used by routing protocols. Not all protocols can use key management. Authentication keys are available for Director Response Protocol (DRP) Agent, EIGRP, and RIP Version 2.
Before you manage authentication keys, authentication must be enabled. See the appropriate protocol chapter to learn how to enable authentication for that protocol.
To manage authentication keys, see the "Managing Authentication Keys" section.
How to Configure IP Routing Protocol-Independent Features
•Configuring Redistribution Routing Information
•Configuring Routing Information Filtering
•Configuring precedence for policy-based routed packets
•Configuring QoS Policy Propagation via BGP
•Monitoring and Maintaining the IP Network
Configuring Redistribution Routing Information
•Defining conditions for redistributing routes
•Redistributing routes from one routing domain to another
•Removing options for redistributing routes
Defining conditions for redistributing routes
To define conditions for redistributing routes from one routing protocol into another, use at least one of the following commands in route map configuration mode, as needed.
To define conditions for redistributing routes from one routing protocol into another, use at least one of the following set commands in route map configuration mode as needed.
Redistributing routes from one routing domain to another
To distribute routes from one routing domain into another routing domain and to control route redistribution, perform the following task.
SUMMARY STEPS
1. redistribute protocol [process-id] {level-1 | level-1-2 | level-2} [metric metric-value] [metric-type type-value] [match internal | external type-value] [tag tag-value] [route-map map-tag] [subnets]
2. default-metric number
3. default-metric bandwidth delay reliability loading mtu
4. no default-information {in | out}
DETAILED STEPS
Removing options for redistributing routes
Removing options that you have configured for the redistribute command requires careful use of the no form of the redistribute command to ensure that you obtain the result that you are expecting.
SUMMARY STEPS
1. no redistribute connected metric 1000 subnets
2. no redistribute connected metric 1000
3. no redistribute connected subnets
4. no redistribute connected
DETAILED STEPS
Configuring Routing Information Filtering
To filter routing protocol information, perform the tasks in the following sections. The tasks in the first section are required; the remaining sections are optional:
•Preventing Routing Updates Through an Interface (required)
•Preventing Routing Updates Through an Interface (optional)
•Controlling the Advertising of Routes in Routing Updates (optional)
•Controlling the Processing of Routing Updates (optional)
•Filtering Sources of Routing Information (optional)
Note When routes are redistributed between OSPF processes, no OSPF metrics are preserved
Preventing Routing Updates Through an Interface
To prevent other routers on a local network from learning about routes dynamically, you can keep routing update messages from being sent through a router interface. Keeping routing update messages from being sent through a router interface prevents other systems on the interface from learning about routes dynamically. This feature applies to all IP-based routing protocols except BGP.
OSPF and IS-IS behave somewhat differently. In OSPF, the interface address that you specify as passive appears as a stub network in the OSPF domain. OSPF routing information is neither sent nor received through the specified router interface. In IS-IS, the specified IP addresses are advertised without actually running IS-IS on those interfaces.
To prevent routing updates through a specified interface, use the passive-interface interface-type interface-number command in router configuration mode. See the "Example: Passive Interface" section for examples of configuring passive interfaces.
Configuring Default Passive Interfaces
To set all interfaces as passive by default and then activate only those interfaces that must have adjacencies set, perform the following task.
SUMMARY STEPS
1. enable
2. configure terminal
3. router protocol
4. passive-interface default
5. no passive-interface interface-type
6. network network-address [options]
7. end
8. show ip ospf interface
9. show ip interface
DETAILED STEPS
See the section "Example: Default Passive Interface" section for an example of a default passive interface.
To verify that interfaces on your network have been set to passive, you could enter a network monitoring command such as the show ip ospf interface command, or you could verify the interfaces that you enabled as active using a command such as the show ip interface command.
Controlling the Advertising of Routes in Routing Updates
To prevent other routers from learning one or more routes, you can suppress routes from being advertised in routing updates. Suppressing routes in route updates prevents other routers from learning the interpretation of a particular device of one or more routes. You cannot specify an interface name in OSPF. When used for OSPF, this feature applies only to external routes.
To suppress routes from being advertised in routing updates, use the distribute-list {access-list-number | access-list-name} out [interface-name | routing-process | as-number] command in router configuration mode.
Controlling the Processing of Routing Updates
You might want to avoid processing certain routes listed in incoming updates. This feature does not apply to OSPF or IS-IS. To suppress routes in incoming updates, use the distribute-list {access-list-number | access-list-name} in [interface-type interface-number] command in router configuration mode.
Filtering Sources of Routing Information
To filter sources of routing information, use the distance ip-address wildcard- mask [ip-standard-acl | ip-extended-acl | access-list-name] command in router configuration mode.
Configuring precedence for policy-based routed packets
To configure the precedence and specify where the packets that pass the match criteria are output, perform the following task.
SUMMARY STEPS
1. set ip precedence {number | name}
2. set ip next-hop ip-address [ip-address]
3. set interface interface-type interface-number [... interface-type interface-number]
4. set ip default next-hop ip-address [ip-address]
5. set default interface interface-type interface-number [... interface-type interface-number]
Detailed Steps
Note The set ip next-hop and set ip default next-hop commands are similar but have a different order of operation. Configuring the set ip next-hop command causes the system to use policy routing first and then use the routing table. Configuring the set ip default next-hop causes the system to use the routing table first and then policy-route the specified next hop.
Configuring QoS Policy Propagation via BGP
The QoS Policy Propagation via BGP feature allows you to classify packets by IP precedence based on BGP community lists, BGP autonomous system paths, and access lists. After a packet has been classified, you can use other QoS features such as committed access rate (CAR) and Weighted Random Early Detection (WRED) to specify and enforce policies to fit your business model.
To configure Policy Propagation via BGP, perform the following basic tasks:
•Configure BGP and Cisco Express Forwarding (CEF) or distributed CEF (dCEF). To configure BGP, refer to the Cisco IOS IP Routing: BGP Configuration Guide. To configure CEF and dCEF, refer to the Cisco IOS IP Switching Configuration Guide.
•Define the policy.
•Apply the policy through BGP.
•Configure the BGP community list, BGP autonomous system path, or access list and enable the policy on an interface. For information about these tasks, see the tasks below.
•Enable CAR or WRED to use the policy. To enable CAR, see the chapter "Configuring Committed Access Rate" in the Cisco IOS Quality of Service Solutions Configuration Guide. To configure WRED, see the chapter "Configuring Weighted Random Early Detection" in the Cisco IOS Quality of Service Solutions Configuration Guide.
This section describes how to configure QoS Policy Propagation based on BGP community list, BGP autonomous system path, or access list. It assumes you have already configured BGP and CEF or dCEF.
To configure QoS Policy Propagation via BGP, perform the tasks described in the following sections. The tasks in the first three sections are required; the task in the remaining section is optional.
•Configuring QoS Policy Propagation Based on Community Lists
•Configuring QoS Policy Propagation Based on the Autonomous System Path Attribute
•Configuring QoS Policy Propagation Based on an Access List
•Monitoring QoS Policy Propagation via BGP
Note For the QoS Policy Propagation via BGP feature to work, you must enable BGP and CEF/dCEF on the router. Subinterfaces on an ATM interface that have the bgp-policy command enabled must use CEF mode because dCEF is not supported. dCEF uses the Versatile Interface Processor (VIP) rather than the Route Switch Processor (RSP) to perform forwarding functions.
For configuration examples, see the "Examples: QoS Policy Propagation via BGP Configuration" section."
Configuring QoS Policy Propagation Based on Community Lists
This section describes how to configure Policy Propagation via BGP using community lists. The tasks listed in this section are required unless noted as optional. This section assumes that you have already configured CEF/dCEF and BGP on your router.
Perform the following task to configure the router to propagate the IP precedence based on the community lists.
SUMMARY STEPS
1. enable
2. configure terminal
3. route-map route-map-name [permit | deny [sequence-number]]
4. match community-list community-list-number [exact]
5. set ip precedence [number | name]
6. exit
7. router bgp autonomous-system
8. table-map route-map-name
9. exit
10. ip community-list community-list-number {permit | deny} community-number
11. interface interface-type interface-number
12. bgp-policy {source | destination} ip-prec-map
13. ip bgp-community new-format
14. end
DETAILED STEPS
Configuring QoS Policy Propagation Based on the Autonomous System Path Attribute
This section describes how to configure QoS Policy Propagation via BGP based on the autonomous system path. This section assumes that you have already configured CEF/dCEF and BGP on your router.
Perform the following task to configure the router to propagate the IP precedence based on the autonomous system path attribute.
SUMMARY STEPS
1. enable
2. configure terminal
3. route-map route-map-name [permit | deny [sequence-number]]
4. match as-path path-list-number
5. set ip precedence [number | name]
6. exit
7. router bgp autonomous-system
8. table-map route-map-name
9. exit
10. ip as-path access-list access-list-number {permit | deny} as-regular-expression
11. interface interface-type interface-number
12. bgp-policy {source | destination} ip-prec-map
13. end
DETAILED STEPS
Configuring QoS Policy Propagation Based on an Access List
This section describes how to configure QoS Policy Propagation via BGP based on an access list. This section assumes you have already configured CEF/dCEF and BGP on your router.
To configure the router to propagate the IP Precedence based on an access list, perform the following task.s
SUMMARY STEPS
1. enable
2. configure terminal
3. route-map route-map-name [permit | deny [sequence-number]]
4. match ip address access-list-number
5. set ip precedence [number | name]
6. exit
7. router bgp autonomous-system
8. table-map route-map-name
9. exit
10. access-list access-list-number {permit | deny} source
11. interface interface-type interface-number
12. bgp-policy {source | destination} ip-prec-map
13. end
DETAILED STEPS
Monitoring QoS Policy Propagation via BGP
To monitor the QoS Policy Propagation via BGP configuration, use the following commands in EXEC mode, as needed. The commands listed in this section are optional.
Managing Authentication Keys
To manage authentication keys, define a key chain, identify the keys that belong to the key chain, and specify how long each key is valid. Each key has its own key identifier (specified with the key key-chain configuration command), which is stored locally. The combination of the key identifier and the interface associated with the message uniquely identifies the authentication algorithm and Message Digest 5 (MD5) authentication key in use.
You can configure multiple keys with lifetimes. Only one authentication packet is sent, regardless of how many valid keys exist. The software examines the key numbers in order from lowest to highest and uses the first valid key that it encounters. The lifetimes allow for overlap during key changes. Note that the router must know the time. Refer to the Network Time Protocol (NTP) and calendar commands in the "Performing Basic System Management" chapter of the Network Management Configuration Guide.
To manage authentication keys, perform the following task.
SUMMARY STEPS
1. enable
2. configure terminal
3. key chain name-of-chain
4. key number
5. key-string text
6. accept-lifetime start-time {infinite | end-time | duration seconds}
7. send-lifetime start-time {infinite | end-time | duration seconds}
8. end
9. show key chain
DETAILED STEPS
For examples of key management, see the "Examples: Key Management" section.
Monitoring and Maintaining the IP Network
You can remove all contents of a particular cache, table, or database. You also can display specific statistics. The following sections describe each of these tasks.
Clearing Routes from the IP Routing Table
You can remove all contents of a particular table. Clearing a table can become necessary when the contents of the particular structure have become, or are suspected to be, invalid.
To clear one or more routes from the IP routing table, use the clear ip route {network [mask] | *} command in EXEC mode.
Displaying System and Network Statistics
You can display specific statistics such as the contents of IP routing tables, caches, and databases. Information provided can be used to determine resource utilization and solve network problems. You can also display information about node reachability and discover the routing path that packets leaving your device are taking through the network.
Configuration Examples for Configuring IP Routing Protocol-Independent Features
•Example: Variable-Length Subnet Mask
•Example: Overriding Static Routes with Dynamic Protocols
•Example: Administrative Distances
•Example: Static Routing Redistribution
•Example: EIGRP Redistribution
•Example: Simple Redistribution
•Example: Complex Redistribution
•Examples: OSPF Routing and Route Redistribution
•Example: Default Metric Values Redistribution
•Example: Policy-Based Routing
•Example: Policy Routing with CEF
•Examples: QoS Policy Propagation via BGP Configuration
Example: Variable-Length Subnet Mask
The following example uses two different subnet masks for the class B network address of 172.16.0.0. A subnet mask of /24 is used for LAN interfaces. The /24 mask allows 256 subnets with 254 host IP addresses on each subnet. The final subnet of the range of possible subnets using a /24 mask (172.16.255.0) is reserved for use on point-to-point interfaces and assigned a longer mask of /30. The use of a /30 mask on 172.16.255.0 creates 64 subnets (172.16.255.0 - 172.16.255.252) with 2 host addresses on each subnet.
Warning To ensure unambiguous routing, you must not assign 172.16.255.0/24 to a LAN interface in your network.
Router(config)# interface Ethernet 0/0
Router(config-if)# ip address 172.16.1.1 255.255.255.0
Router(config-if)# ! 8 bits of host address space reserved for Ethernet interfaces
Router(config-if)# exit
Router(config)# interface Serial 0/0
Router(config-if)# ip address 172.16.255.5 255.255.255.252
Router(config-if)# ! 2 bits of address space reserved for point-to-point serial interfaces
Router(config-if)# exit
Router(config)# router rip
Router(config-router)# network 172.16.0.0
Router(config-router)# ! Specifies the network directly connected to the router
Example: Overriding Static Routes with Dynamic Protocols
In the following example, packets for network 10.0.0.0 from Router B (where the static route is installed) will be routed through 172.18.3.4 if a route with an administrative distance less than 110 is not available. Figure 1 illustrates this example. The route learned by a protocol with an administrative distance of less than 110 might cause Router B to send traffic destined for network 10.0.0.0 via the alternate path—through Router D.
Router(config)# ip route 10.0.0.0 255.0.0.0 172.18.3.4 110
Figure 1 Overriding Static Routes
Example: Administrative Distances
In the following example, the router eigrp global configuration command configures EIGRP routing in autonomous system 1. The network command configuration specifies EIGRP routing on networks 192.168.7.0 and 172.16.0.0. The first distance router configuration command sets the default administrative distance to 255, which instructs the router to ignore all routing updates from routers for which an explicit distance has not been set. The second distance command sets the administrative distance to 80 for internal EIGRP routes and to 100 for external EIGRP routes. The third distance command sets the administrative distance to 120 for the router with the address 172.16.1.3.
Router(config)# router eigrp 1
Router(config-router)# network 192.168.7.0
Router(config-router)# network 172.16.0.0
Router(config-router)# distance 255
Router(config-router)# distance eigrp 80 100
Router(config-router)# distance 120 172.16.1.3 0.0.0.0
Note The distance eigrp command must be used to set the administrative distance for EIGRP-derived routes.
The following example assigns the router with the address 192.168.7.18 an administrative distance of 100 and all other routers on subnet 192.168.7.0 an administrative distance of 200:
Router(config-router)# distance 100 192.168.7.18 0.0.0.0
Router(config-router)# distance 200 192.168.7.0 0.0.0.255
However, if you reverse the order of these two commands, all routers on subnet 192.168.7.0 are assigned an administrative distance of 200, including the router at address 192.168.7.18:
Router(config-router)# distance 200 192.168.7.0 0.0.0.255
Router(config-router)# distance 100 192.168.7.18 0.0.0.0
Note Assigning administrative distances can be used to solve unique problems. However, administrative distances should be applied carefully and consistently to avoid the creation of routing loops or other network failures.
In the following example, the distance value for IP routes learned is 90. Preference is given to these IP routes rather than routes with the default administrative distance value of 110.
Router(config)# router isis
Router(config-router)# distance 90 ip
Example: Static Routing Redistribution
In the example that follows, three static routes are specified, two of which are to be advertised. The static routes are created by specifying the redistribute static router configuration command and then specifying an access list that allows only those two networks to be passed to the EIGRP process. Any redistributed static routes should be sourced by a single router to minimize the likelihood of creating a routing loop.
Router(config)# ip route 192.168.2.0 255.255.255.0 192.168.7.65
Router(config)# ip route 192.168.5.0 255.255.255.0 192.168.7.65
Router(config)# ip route 10.10.10.0 255.255.255.0 10.20.1.2
Router(config)# !
Router(config)# access-list 3 permit 192.168.2.0 0.0.255.255
Router(config)# access-list 3 permit 192.168.5.0 0.0.255.255
Router(config)# access-list 3 permit 10.10.10.0 0.0.0.255
Router(config)# !
Router(config)# router eigrp 1
Router(config-router)# network 192.168.0.0
Router(config-router)# network 10.10.10.0
Router(config-router)# redistribute static metric 10000 100 255 1 1500
Router(config-router)# distribute-list 3 out static
Example: EIGRP Redistribution
Each EIGRP routing process provides routing information to only one autonomous system. The Cisco IOS software must run a separate EIGRP process and maintain a separate routing database for each autonomous system that it services. However, you can transfer routing information between these routing databases.
In the following configuration, network 10.0.0.0 is configured under EIGRP autonomous system 1 and network 192.168.7.0 is configured under EIGRP autonomous system 101:
Router(config)# router eigrp 1
Router(config-router)# network 10.0.0.0
Router(config-router)# exit
Router(config)# router eigrp 101
Router(config-router)# network 192.168.7.0
In the following example, routes from the 192.168.7.0 network are redistributed into autonomous system 1 (without passing any other routing information from autonomous system 101):
Router(config)# access-list 3 permit 192.168.7.0
Router(config)# !
Router(config)# route-map 101-to-1 permit 10
Router(config-route-map)# match ip address 3
Router(config-route-map)# set metric 10000 100 1 255 1500
Router(config-route-map)# exit
Router(config)# router eigrp 1
Router(config-router)# redistribute eigrp 101 route-map 101-to-1
Router(config-router)#!
The following example is an alternative way to redistribute routes from the 192.168.7.0 network into autonomous system 1. Unlike the previous configuration, this method does not allow you to set the metric for redistributed routes.
Router(config)# access-list 3 permit 192.168.7.0
Router(config)# !
Router(config)# router eigrp 1
Router(config-router)# redistribute eigrp 101
Router(config-router)# distribute-list 3 out eigrp 101
Router(config-router)# !
Example: Simple Redistribution
Consider a WAN at a university that uses RIP as an interior routing protocol. Assume that the university wants to connect its WAN to a regional network, 172.16.0.0, which uses EIGRP as the routing protocol. The goal in this case is to advertise the networks in the university network to the routers on the regional network.
In the following example, EIGRP-to-RIP redistribution is configured:
Router(config)# access-list 10 permit 172.16.0.0
Router(config)# !
Router(config)# router eigrp 1
Router(config-router)# network 172.16.0.0
Router(config-router)# redistribute rip metric 10000 100 255 1 1500
Router(config-router)# distribute-list 10 out rip
Router(config-router)# exit
Router(config)# router rip
Router(config-router)# redistribute eigrp 1
Router(config-router)# !
In this example, an EIGRP routing process is started. The network router configuration command specifies that network 172.16.0.0 (the regional network) is to send and receive EIGRP routing information. The redistribute router configuration command specifies that RIP-derived routing information be advertised in the routing updates. The default-metric router configuration command assigns an EIGRP metric to all RIP-derived routes. The distribute-list router configuration command instructs the Cisco IOS software to use access list 10 (not defined in this example) to limit the entries in each outgoing update. The access list prevents unauthorized advertising of university routes to the regional network.
Example: Complex Redistribution
In the following example, mutual redistribution is configured between EIGRP and BGP.
Routes from BGP autonomous system 50000 are injected into EIGRP routing process 101. A filter is configured to ensure that the correct routes are advertised.
Router(config)# ! All networks that should be advertised from R1 are controlled with ACLs:
Router(config)# access-list 1 permit 172.18.0.0 0.0.255.255
Router(config)# access-list 1 permit 172.16.0.0 0.0.255.255
Router(config)# access-list 1 permit 172.25.0.0 0.0.255.255
Router(config)# ! Configuration for router R1:
Router(config)# router bgp 50000
Router(config-router)# network 172.18.0.0
Router(config-router)# network 172.16.0.0
Router(config-router)# neighbor 192.168.10.1 remote-as 2
Router(config-router)# neighbor 192.168.10.15 remote-as 1
Router(config-router)# neighbor 192.168.10.24 remote-as 3
Router(config-router)# redistribute eigrp 101
Router(config-router)# distribute-list 1 out eigrp 101
Router(config-router)# exit
Router(config)# router eigrp 101
Router(config-router)# network 172.25.0.0
Router(config-router)# redistribute bgp 50000
Router(config-router)# distribute-list 1 out bgp 50000
Router(config-router)# !
BGP should be redistributed into an IGP when there are no other suitable options. Redistribution from BGP into any IGP should be applied with proper filtering using distribute-lists, IP prefix-list, and route map statements to limit the number of prefixes. BGP routing tables can be very large. Redistributing all BGP prefixes into an IGP can have a detrimental effect on IGP network operations.
Examples: OSPF Routing and Route Redistribution
OSPF typically requires coordination among many internal routers, Area Border Routers (ABRs), and Autonomous System Boundary Routers (ASBRs). At a minimum, OSPF-based routers can be configured with all default parameter values, with no authentication, and with interfaces assigned to areas.
Three types of examples follow:
•The first examples are simple configurations illustrating basic OSPF commands.
•The second example illustrates a configuration for an internal router, ABR, and ASBRs within a single, arbitrarily assigned, OSPF autonomous system.
•The third example illustrates a more complex configuration and the application of various tools available for controlling OSPF-based routing environments.
Examples: Basic OSPF Configuration
The following example illustrates a simple OSPF configuration that enables OSPF routing process 1, attaches Ethernet interface 0 to area 0.0.0.0, and redistributes RIP into OSPF and OSPF into RIP:
Router(config)# interface Ethernet 0
Router(config-if)# ip address 172.16.1.1 255.255.255.0
Router(config-if)# ip ospf cost 1
Router(config-if)# exit
Router(config)# interface Ethernet 1
Router(config-if)# ip address 172.17.1.1 255.255.255.0
Router(config-if)# exit
Router(config)# router ospf 1
Router(config-router)# network 172.18.0.0 0.0.255.255 area 0.0.0.0
Router(config-router)# redistribute rip metric 1 subnets
Router(config-router)# exit
Router(config)# router rip
Router(config-router)# network 172.17.0.0
Router(config-router)# redistribute ospf 1
Router(config-router)# default-metric 1
Router(config-router)# !
The following example illustrates the assignment of four area IDs to four IP address ranges. In the example, OSPF routing process 1 is initialized, and four OSPF areas are defined: 10.9.50.0, 2, 3, and 0. Areas 10.9.50.0, 2, and 3 mask-specific address ranges, whereas area 0 enables OSPF for all other networks.
Router(config)# router ospf 1
Router(config-router)# network 172.18.20.0 0.0.0.255 area 10.9.50.0
Router(config-router)# network 172.18.0.0 0.0.255.255 area 2
Router(config-router)# network 172.19.10.0 0.0.0.255 area 3
Router(config-router)# network 0.0.0.0 255.255.255.255 area 0
Router(config-router)# exit
Router(config)# ! Ethernet interface 0 is in area 10.9.50.0:
Router(config)# interface Ethernet 0
Router(config-if)# ip address 172.18.20.5 255.255.255.0
Router(config-if)# exit
Router(config)# ! Ethernet interface 1 is in area 2:
Router(config)# interface Ethernet 1
Router(config-if)# ip address 172.18.1.5 255.255.255.0
Router(config-if)# exit
Router(config)# ! Ethernet interface 2 is in area 2:
Router(config)# interface Ethernet 2
Router(config-if)# ip address 172.18.2.5 255.255.255.0
Router(config-if)# exit
Router(config)# ! Ethernet interface 3 is in area 3:
Router(config)# interface Ethernet 3
Router(config-if)# ip address 172.19.10.5 255.255.255.0
Router(config-if)# exit
Router(config)# ! Ethernet interface 4 is in area 0:
Router(config)# interface Ethernet 4
Router(config-if)# ip address 172.19.1.1 255.255.255.0
Router(config-if)# exit
Router(config)# ! Ethernet interface 5 is in area 0:
Router(config)# interface Ethernet 5
Router(config-if)# ip address 10.1.0.1 255.255.0.0
Router(config-if)# !
Each network router configuration command is evaluated sequentially, so the specific order of these commands in the configuration is important. The Cisco IOS software sequentially evaluates the address/wildcard-mask pair for each interface. See the Cisco IOS IP Routing: Protocol-Independent Command Reference for more information.
Consider the first network command. Area ID 10.9.50.0 is configured for the interface on which subnet 172.18.20.0 is located. Assume that a match is determined for Ethernet interface 0. Ethernet interface 0 is attached to Area 10.9.50.0 only.
The second network command is evaluated next. For Area 2, the same process is then applied to all interfaces (except Ethernet interface 0). Assume that a match is determined for Ethernet interface 1. OSPF is then enabled for that interface, and Ethernet 1 is attached to Area 2.
This process of attaching interfaces to OSPF areas continues for all network commands. Note that the last network command in this example is a special case. With this command, all available interfaces (not explicitly attached to another area) are attached to Area 0.
Example: Internal Router, ABR, and ASBRs Configuration
Figure 2 provides a general network map that illustrates a sample configuration for several routers within a single OSPF autonomous system.
Figure 2 Example OSPF Autonomous System Network Map
In this configuration, five routers are configured in OSPF autonomous system 1:
•Router A and Router B are both internal routers within area 1.
•Router C is an OSPF ABR. Note that for Router C, area 1 is assigned to E3 and Area 0 is assigned to S0.
•Router D is an internal router in area 0 (backbone area). In this case, both network router configuration commands specify the same area (area 0, or the backbone area).
•Router E is an OSPF ASBR. Note that BGP routes are redistributed into OSPF and that these routes are advertised by OSPF.
Note It is not necessary to include definitions of all areas in an OSPF autonomous system in the configuration of all routers in the autonomous system. You must define only the directly connected areas. In the example that follows, routes in Area 0 are learned by the routers in area 1 (Router A and Router B) when the ABR (Router C) injects summary LSAs into area 1.
Autonomous system 60000 is connected to the outside world via the BGP link to the external peer at IP address 172.16.1.6.
Following is the example configuration for the general network map shown in Figure 2.
Router A Configuration—Internal Router
Router(config)# interface Ethernet 1
Router(config-if)# ip address 192.168.1.1 255.255.255.0
Router(config-if)# exit
Router(config)# router ospf 1
Router(config-router)# network 192.168.1.0 0.0.0.255 area 1
Router(config-router)# exit
Router B Configuration—Internal Router
Router(config)# interface Ethernet 2
Router(config-if)# ip address 192.168.1.2 255.255.255.0
Router(config-if)# exit
Router(config)# router ospf 1
Router(config-router)# network 192.168.1.0 0.0.0.255 area 1
Router(config-router)# exit
Router C Configuration—ABR
Router(config)# interface Ethernet 3
Router(config-if)# ip address 192.168.1.3 255.255.255.0
Router(config-if)# exit
Router(config)# interface Serial 0
Router(config-if)# ip address 192.168.2.3 255.255.255.0
Router(config-if)# exit
Router(config)# router ospf 1
Router(config-router)# network 192.168.1.0 0.0.0.255 area 1
Router(config-router)# network 192.168.2.0 0.0.0.255 area 0
Router(config-router)# exit
Router D Configuration—Internal Router
Router(config)# interface Ethernet 4
Router(config-if)# ip address 10.0.0.4 255.0.0.0
Router(config-if)# exit
Router(config)# interface Serial 1
Router(config-if)# ip address 192.168.2.4 255.255.255.0
Router(config-if)# exit
Router(config)# router ospf 1
Router(config-router)# network 192.168.2.0 0.0.0.255 area 0
Router(config-router)# network 10.0.0.0 0.255.255.255 area 0
Router(config-router)# exit
Router E Configuration—ASBR
Router(config)# interface Ethernet 5
Router(config-if)# ip address 10.0.0.5 255.0.0.0
Router(config-if)# exit
Router(config)# interface Serial 2
Router(config-if)# ip address 172.16.1.5 255.255.255.0
Router(config-if)# exit
Router(config)# router ospf 1
Router(config-router)# network 10.0.0.0 0.255.255.255 area 0
Router(config-router)# redistribute bgp 50000 metric 1 metric-type 1
Router(config-router)# exit
Router(config)# router bgp 50000
Router(config-router)# network 192.168.0.0
Router(config-router)# network 10.0.0.0
Router(config-router)# neighbor 172.16.1.6 remote-as 60000
Example: Complex OSPF Configuration
The following example configuration accomplishes several tasks in setting up an ABR. These tasks can be split into two general categories:
•Basic OSPF configuration
•Route redistribution
The specific tasks outlined in this configuration are detailed briefly in the following descriptions. Figure 3 illustrates the network address ranges and area assignments for the interfaces.
Figure 3 Interface and Area Specifications for OSPF Configuration Example
The basic configuration tasks in this example are as follows:
•Configure address ranges for Ethernet interface 0 through Ethernet interface 3.
•Enable OSPF on each interface.
•Set up an OSPF authentication password for each area and network.
•Assign link-state metrics and other OSPF interface configuration options.
•Create a stub area with area ID 10.0.0.0. (Note that the authentication and stub options of the area router configuration command are specified with separate area command entries, but they can be merged into a single area command.)
•Specify the backbone area (area 0).
Configuration tasks associated with redistribution are as follows:
•Redistribute EIGRP and RIP into OSPF with various options set (including metric-type, metric, tag, and subnet).
•Redistribute EIGRP and OSPF into RIP.
The following is an example OSPF configuration:
Router(config)# interface Ethernet 0
Router(config-if)# ip address 192.168.110.201 255.255.255.0
Router(config-if)# ip ospf authentication-key abcdefgh
Router(config-if)# ip ospf cost 10
Router(config-if)# exit
Router(config)# interface Ethernet 1
Router(config-if)# ip address 172.19.251.201 255.255.255.0
Router(config-if)# ip ospf authentication-key ijklmnop
Router(config-if)# ip ospf cost 20
Router(config-if)# ip ospf retransmit-interval 10
Router(config-if)# ip ospf transmit-delay 2
Router(config-if)# ip ospf priority 4
Router(config-if)# exit
Router(config)# interface Ethernet 2
Router(config-if)# ip address 172.19.254.201 255.255.255.0
Router(config-if)# ip ospf authentication-key abcdefgh
Router(config-if)# ip ospf cost 10
Router(config-if)# exit
Router(config)# interface Ethernet 3
Router(config-if)# ip address 10.56.0.201 255.255.0.0
Router(config-if)# ip ospf authentication-key ijklmnop
Router(config-if)# ip ospf cost 20
Router(config-if)# ip ospf dead-interval 80
Router(config-if)# exit
In the following configuration, OSPF is on network 172.19.0.0:
Router(config)# router ospf 1
Router(config-router)# network 10.0.0.0 0.255.255.255 area 10.0.0.0
Router(config-router)# network 192.168.110.0 0.0.0.255 area 192.68.110.0
Router(config-router)# network 172.19.0.0 0.0.255.255 area 0
Router(config-router)# area 0 authentication
Router(config-router)# area 10.0.0.0 stub
Router(config-router)# area 10.0.0.0 authentication
Router(config-router)# area 10.0.0.0 default-cost 20
Router(config-router)# area 192.168.110.0 authentication
Router(config-router)# area 10.0.0.0 range 10.0.0.0 255.0.0.0
Router(config-router)# area 192.168.110.0 range 192.168.110.0 255.255.255.0
Router(config-router)# area 0 range 172.19.251.0 255.255.255.0
Router(config-router)# area 0 range 172.19.254.0 255.255.255.0
Router(config-router)# redistribute eigrp 200 metric-type 2 metric 1 tag 200 subnets
Router(config-router)# redistribute rip metric-type 2 metric 1 tag 200
Router(config-router)# exit
In the following configuration, EIGRP autonomous system 1 is on 172.19.0.0:
Router(config)# router eigrp 1
Router(config-router)# network 172.19.0.0
Router(config-router)# exit
Router(config)# ! RIP for 192.168.110.0:
Router(config)# router rip
Router(config-router)# network 192.168.110.0
Router(config-router)# redistribute eigrp 1 metric 1
Router(config-router)# redistribute ospf 201 metric 1
Router(config-router)# exit
Example: Default Metric Values Redistribution
The following example shows a router in autonomous system 1 that is configured to run both RIP and EIGRP. The example advertises EIGRP-derived routes using RIP and assigns the EIGRP-derived routes a RIP metric of 10.
Router(config)# router rip
Router(config-router)# default-metric 10
Router(config-router)# redistribute eigrp 1
Router(config-router)# exit
Example: Route Map
The examples in this section illustrate the use of redistribution, with and without route maps. Examples from both the IP and Connectionless Network Service (CLNS) routing protocols are given. The following example redistributes all OSPF routes into EIGRP:
Router(config)# router eigrp 1
Router(config-router)# redistribute ospf 101
Router(config-router)# exit
The following example redistributes RIP routes with a hop count equal to 1 into OSPF. These routes will be redistributed into OSPF as external LSAs with a metric of 5, metric a type of type 1, and a tag equal to 1.
Router(config)# router ospf 1
Router(config-router)# redistribute rip route-map rip-to-ospf
Router(config-router)# exit
Router(config)# route-map rip-to-ospf permit
Router(config-route-map)# match metric 1
Router(config-route-map)# set metric 5
Router(config-route-map)# set metric-type type 1
Router(config-route-map)# set tag 1
Router(config-route-map)# exit
The following example redistributes OSPF learned routes with tag 7 as a RIP metric of 15:
Router(config)# router rip
Router(config-router)# redistribute ospf 1 route-map 5
Router(config-router)# exit
Router(config)# route-map 5 permit
Router(config-route-map)# match tag 7
Router(config-route-map)# set metric 15
The following example redistributes OSPF intra-area and interarea routes with next hop routers on serial interface 0 into BGP with an INTER_AS metric of 5:
Router(config)# router bgp 50000
Router(config-router)# redistribute ospf 1 route-map 10
Router(config-router)# exit
Router(config)# route-map 10 permit
Router(config-route-map)# match route-type internal
Router(config-route-map)# match interface serial 0
Router(config-route-map)# set metric 5
The following example redistributes two types of routes into the integrated IS-IS routing table (supporting both IP and CLNS). The first type is OSPF external IP routes with tag 5; these routes are inserted into Level 2 IS-IS link-state packets (LSPs) with a metric of 5. The second type is ISO-IGRP derived CLNS prefix routes that match CLNS access list 2000; these routes will be redistributed into IS-IS as Level 2 LSPs with a metric of 30.
Router(config)# router isis
Router(config-router)# redistribute ospf 1 route-map 2
Router(config-router)# redistribute iso-igrp nsfnet route-map 3 Router(config-router)# exit
Router(config)# route-map 2 permit
Router(config-route-map)# match route-type external
Router(config-route-map)# match tag 5
Router(config-route-map)# set metric 5
Router(config-route-map)# set level level-2
Router(config-route-map)# exit
Router(config)# route-map 3 permit
Router(config-route-map)# match address 2000
Router(config-route-map)# set metric 30
Router(config-route-map)# exit
With the following configuration, OSPF external routes with tags 1, 2, 3, and 5 are redistributed into RIP with metrics of 1, 1, 5, and 5, respectively. The OSPF routes with a tag of 4 are not redistributed.
Router(config)# router rip
Router(config-router)# redistribute ospf 101 route-map 1
Router(config-router)# exit
Router(config)# route-map 1 permit
Router(config-route-map)# match tag 1 2
Router(config-route-map)# set metric 1
Router(config-route-map)# exit
Router(config)# route-map 1 permit
Router(config-route-map)# match tag 3
Router(config-route-map)# set metric 5
Router(config-route-map)# exit
Router(config)# route-map 1 deny
Router(config-route-map)# match tag 4
Router(config-route-map)# exit
Router(config)# route map 1 permit
Router(config-route-map)# match tag 5
Router(config-route-map)# set metric 5
Router(config-route-map)# exit
Given the following configuration, a RIP learned route for network 172.18.0.0 and an ISO-IGRP learned route with prefix 49.0001.0002 will be redistributed into an IS-IS Level 2 LSP with a metric of 5:
Router(config)# router isis
Router(config-router)# redistribute rip route-map 1
Router(config-router)# redistribute iso-igrp remote route-map 1
Router(config-router)# exit
Router(config)# route-map 1 permit
Router(config-route-map)# match ip address 1
Router(config-route-map)# match clns address 2
Router(config-route-map)# set metric 5
Router(config-route-map)# set level level-2
Router(config-route-map)# exit
Router(config)# access-list 1 permit 172.18.0.0 0.0.255.255
Router(config)# clns filter-set 2 permit 49.0001.0002...
The following configuration example illustrates how a route map is referenced by the default-information router configuration command. This type of reference is called conditional default origination. OSPF will originate the default route (network 0.0.0.0) with a type 2 metric of 5 if 172.20.0.0 is in the routing table.
Router(config)# route-map ospf-default permit
Router(config-route-map)# match ip address 1
Router(config-route-map)# set metric 5
Router(config-route-map)# set metric-type type-2
Router(config-route-map)# exit
Router(config)# access-list 1 172.20.0.0 0.0.255.255
Router(config)# router ospf 101
Router(config-router)# default-information originate route-map ospf-default
See the "Connecting to a Service Provider Using External BGP" module for more examples of BGP route-map configuration tasks and configuration examples.
Example: Passive Interface
In OSPF, hello packets are not sent on an interface that is specified as passive. Hence, the router will not be able to discover any neighbors, and none of the OSPF neighbors will be able to see the router on that network. In effect, this interface will appear as a stub network to the OSPF domain. This configuration is useful if you want to import routes associated with a connected network into the OSPF domain without any OSPF activity on that interface.
The passive-interface router configuration command is typically used when the wildcard specification on the network router configuration command configures more interfaces than is desirable. The following configuration causes OSPF to run on all subnets of 172.18.0.0:
Router(config)# interface Ethernet 0
Router(config-if)# ip address 172.18.1.1 255.255.255.0
Router(config-if)# exit
Router(config)# interface Ethernet 1
Router(config-if)# ip address 172.18.2.1 255.255.255.0
Router(config-if)# exit
Router(config)# interface Ethernet 2
Router(config-if)# ip address 172.18.3.1 255.255.255.0
Router(config-if)# exit
Router(config)# router ospf 1
Router(config-router)# network 172.18.0.0 0.0.255.255 area 0 Router(config-router)# exit
If you do not want OSPF to run on 172.18.3.0, enter the following commands:
Router(config)# router ospf 1
Router(config-router)# network 172.18.0.0 0.0.255.255 area 0
Router(config-router)# passive-interface Ethernet 2
Router(config-router)# exit
Example: Default Passive Interface
The following example configures the network interfaces, sets all interfaces that are running OSPF as passive, and then enables serial interface 0:
Router(config)# interface Ethernet 0
Router(config-if)# ip address 172.19.64.38 255.255.255.0 secondary
Router(config-if)# ip address 172.19.232.70 255.255.255.240
Router(config-if)# no ip directed-broadcast
Router(config-if)# exit
Router(config)# interface Serial 0
Router(config-if)# ip address 172.24.101.14 255.255.255.252
Router(config-if)# no ip directed-broadcast
Router(config-if)# no ip mroute-cache
Router(config-if)# exit
Router(config)# interface TokenRing 0
Router(config-if)# ip address 172.20.10.4 255.255.255.0
Router(config-if)# no ip directed-broadcast
Router(config-if)# no ip mroute-cache
Router(config-if)# ring-speed 16
Router(config-if)# exit
Router(config)# router ospf 1
Router(config-router)# passive-interface default
Router(config-router)# no passive-interface Serial 0
Router(config-router)# network 172.16.10.0 0.0.0.255 area 0
Router(config-router)# network 172.19.232.0 0.0.0.255 area 4
Router(config-router)# network 172.24.101.0 0.0.0.255 area 4
Router(config-router)# exit
Example: Policy-Based Routing
The following example provides two sources with equal access to two different service providers. Packets that arrive on asynchronous interface 1 from the source 10.1.1.1 are sent to the router at 172.16.6.6 if the router has no explicit route for the destination of the packet. Packets that arrive from the source 172.17.2.2 are sent to the router at 192.168.7.7 if the router has no explicit route for the destination of the packet. All other packets for which the router has no explicit route to the destination are discarded.
Router(config)# access-list 1 permit ip 10.1.1.1
Router(config)# access-list 2 permit ip 172.17.2.2
Router(config)# interface async 1
Router(config-if)# ip policy route-map equal-access
Router(config-if)# exit
Router(config)# route-map equal-access permit 10
Router(config-route-map)# match ip address 1
Router(config-route-map)# set ip default next-hop 172.16.6.6
Router(config-route-map)# exit
Router(config)# route-map equal-access permit 20
Router(config-route-map)# match ip address 2
Router(config-route-map)# set ip default next-hop 192.168.7.7
Router(config-route-map)# exit
Router(config)# route-map equal-access permit 30
Router(config-route-map)# set default interface null 0
Router(config-route-map)# exit
Example: Policy Routing with CEF
The following example configures policy routing with CEF. The route is configured to verify that next hop 10.0.0.8 of the route map named test1 is a CDP neighbor before the router tries to policy-route to it.
Router(config)# ip cef
Router(config)# interface Ethernet 0/0/1
Router(config-if)# ip route-cache flow
Router(config-if)# ip policy route-map test
Router(config-if)# exit
Router(config)# route-map test permit 10
Router(config-route-map)# match ip address 1
Router(config-route-map)# set ip precedence priority
Router(config-route-map)# set ip next-hop 10.0.0.8
Router(config-route-map)# set ip next-hop verify-availability
Router(config-route-map)# exit
Router(config)# route-map test permit 20
Router(config-route-map)# match ip address 101
Router(config-route-map)# set interface Ethernet 0/0/3
Router(config-route-map)# set ip tos max-throughput
Router(config-route-map)# exit
Examples: QoS Policy Propagation via BGP Configuration
The following example shows how to create route maps to match access lists, BGP community lists, and BGP autonomous system paths, and apply IP precedence to routes learned from neighbors.
For information on how to configure QoS Policy Propagation via BGP, see the section "Configuring QoS Policy Propagation via BGP" in this document.
In Figure 4, Router A (Cisco 10000 Series) learns routes from autonomous system 10 and autonomous system 60. QoS policy is applied to all packets that match the defined route maps. Any packets from Router A (Cisco 10000 Series) to autonomous system 10 or autonomous system 60 are sent the appropriate QoS policy, as the numbered steps indicate.
Figure 4 Router Learning Routes and Applying QoS Policy
Router A (Cisco 10000 Series) Configuration
interface serial 5/0/0/1:0
ip address 10.28.38.2 255.255.255.0
bgp-policy destination ip-prec-map
no ip mroute-cache
no cdp enable
frame-relay interface-dlci 20 IETF
router bgp 30
table-map precedence-map
neighbor 10.20.20.1 remote-as 10
neighbor 10.20.20.1 send-community
!
ip bgp-community new-format
!
! Match community 1 and set the IP Precedence to priority
route-map precedence-map permit 10
match community 1
set ip precedence priority
!
! Match community 2 and set the IP Precedence to immediate
route-map precedence-map permit 20
match community 2
set ip precedence immediate
!
! Match community 3 and set the IP Precedence to flash
route-map precedence-map permit 30
match community 3
set ip precedence flash
!
! Match community 4 and set the IP Precedence to flash-override
route-map precedence-map permit 40
match community 4
set ip precedence flash-override
!
! Match community 5 and set the IP Precedence to critical
route-map precedence-map permit 50
match community 5
set ip precedence critical
!
! Match community 6 and set the IP Precedence to internet
route-map precedence-map permit 60
match community 6
set ip precedence internet
!
! Match community 7 and set the IP Precedence to network
route-map precedence-map permit 70
match community 7
set ip precedence network
!
! Match ip address access list 69 or match AS path 1
! and set the IP Precedence to critical
route-map precedence-map permit 75
match ip address 69
match as-path 1
set ip precedence critical
!
! For everything else, set the IP Precedence to routine
route-map precedence-map permit 80
set ip precedence routine
!
! Define the community lists
ip community-list 1 permit 60:1
ip community-list 2 permit 60:2
ip community-list 3 permit 60:3
ip community-list 4 permit 60:4
ip community-list 5 permit 60:5
ip community-list 6 permit 60:6
ip community-list 7 permit 60:7
!
! Define the AS path
ip as-path access-list 1 permit ^10_60
!
! Define the access list
access-list 69 permit 10.69.0.0
Router B Configuration
router bgp 10
neighbor 10.30.30.1 remote-as 30
neighbor 10.30.30.1 send-community
neighbor 10.30.30.1 route-map send_community out
!
ip bgp-community new-format
!
! Match prefix 10 and set community to 60:1
route-map send_community permit 10
match ip address 10
set community 60:1
!
! Match prefix 20 and set community to 60:2
route-map send_community permit 20
match ip address 20
set community 60:2
!
! Match prefix 30 and set community to 60:3
route-map send_community permit 30
match ip address 30
set community 60:3
!
! Match prefix 40 and set community to 60:4
route-map send_community permit 40
match ip address 40
set community 60:4
!
! Match prefix 50 and set community to 60:5
route-map send_community permit 50
match ip address 50
set community 60:5
!
! Match prefix 60 and set community to 60:6
route-map send_community permit 60
match ip address 60
set community 60:6
!
! Match prefix 70 and set community to 60:7
route-map send_community permit 70
match ip address 70
set community 60:7
!
! For all others, set community to 60:8
route-map send_community permit 80
set community 60:8
!
! Define the access lists
access-list 10 permit 10.61.0.0
access-list 20 permit 10.62.0.0
access-list 30 permit 10.63.0.0
access-list 40 permit 10.64.0.0
access-list 50 permit 10.65.0.0
access-list 60 permit 10.66.0.0
access-list 70 permit 10.67.0.0
Examples: Key Management
The following example configures a key chain named trees. In this example, the software will always accept and send willow as a valid key. The key chestnut will be accepted from 1:30 p.m. to 3:30 p.m. and be sent from 2:00 p.m. to 3:00 p.m. The overlap allows for migration of keys or discrepancy in the set time of the router. Likewise, the key birch immediately follows chestnut, and there is a 30-minute leeway on each side to handle time-of-day differences.
Router(config)# interface Ethernet 0
Router(config-if)# ip rip authentication key-chain trees
Router(config-if)# ip rip authentication mode md5
Router(config-if)# exit
Router(config)# router rip
Router(config-router)# network 172.19.0.0
Router(config-router)# version 2
Router(config-router)# exit
Router(config)# key chain trees
Router(config-keychain)# key 1
Router(config-keychain-key)# key-string willow
Router(config-keychain-key)# key 2
Router(config-keychain-key)# key-string chestnut
Router(config-keychain-key)# accept-lifetime 13:30:00 Jan 25 2005 duration 7200
Router(config-keychain-key)# send-lifetime 14:00:00 Jan 25 2005 duration 3600
Router(config-keychain-key)# key 3
Router(config-keychain-key)# key-string birch
Router(config-keychain-key)# accept-lifetime 14:30:00 Jan 25 2005 duration 7200
Router(config-keychain-key)# send-lifetime 15:00:00 Jan 25 2005 duration 3600
Router(config-keychain-key)# exit
The following example configures a key chain named trees:
Router(config)# key chain trees
Router(config-keychain)# key 1
Router(config-keychain-key)# key-string willow
Router(config-keychain-key)# key 2
Router(config-keychain-key)# key-string chestnut
Router(config-keychain-key)# accept-lifetime 00:00:00 Dec 5 2004 23:59:59 Dec 5 2005
Router(config-keychain-key)# send-lifetime 06:00:00 Dec 5 2004 18:00:00 Dec 5 2005
Router(config-keychain-key)# exit
Router(config-keychain)# exit
Router(config)# interface Ethernet 0
Router(config-if)# ip address 172.19.104.75 255.255.255.0 secondary 172.19.232.147 255.255.255.240
Router(config-if)# ip rip authentication key-chain trees
Router(config-if)# media-type 10BaseT
Router(config-if)# exit
Router(config)# interface Ethernet 1
Router(config-if)# no ip address
Router(config-if)# shutdown
Router(config-if)# media-type 10BaseT
Router(config-if)# exit
Router(config)# interface Fddi 0
Router(config-if)# ip address 10.1.1.1 255.255.255.0
Router(config-if)# no keepalive
Router(config-if)# exit
Router(config)# interface Fddi 1
Router(config-if)# ip address 172.16.1.1 255.255.255.0
Router(config-if)# ip rip send version 1
Router(config-if)# ip rip receive version 1
Router(config-if)# no keepalive
Router(config-if)# exit
Router(config)# router rip
Router(config-router)# version 2
Router(config-router)# network 172.19.0.0
Router(config-router)# network 10.0.0.0
Router(config-router)# network 172.16.0.0
Additional References
Related Documents
|
|
|
|---|---|
Cisco IOS commands |
|
IP Routing Protocol Independent Commands |
Standards
|
|
|
|---|---|
No new or modified standards are supported, and support for existing standards has not been modified. |
— |
MIBs
|
|
|
|---|---|
None |
To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs
|
|
|
|---|---|
None |
— |
Technical Assistance
Feature Information for Configuring IP Routing Protocol-Independent Features
Table 3 lists the features in this module and provides links to specific configuration information.
Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 3 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.
|
|
|
|
|---|---|---|
Default Passive Interface |
12.0 |
In Internet service provider (ISP) and large enterprise networks, many of the distribution routers have more than 200 interfaces. Obtaining routing information from these interfaces required configuration of the routing protocol on all interfaces and manual configuration of the passive-interface command on the interfaces where adjacency was not desired. The Default Passive Interface feature simplifies the configuration of distribution routers by allowing all interfaces to be set as passive by default using a single passive-interface default command, and then by configuring individual interfaces where adjacencies are desired using the no passive-interface command. The following sections provide information about this feature: • |
Fast-Switched Policy Routing |
11.3 |
IP policy routing can also be fast-switched. Prior to fast-switched policy routing, policy routing could only be process-switched, which meant that on most platforms, the switching rate was approximately 1000 to 10,000 packets per second. Such rates were not fast enough for many applications. Users that need policy routing to occur at faster speeds can now implement policy routing without slowing down the router. The following sections provide information about this feature: |
IP Routing |
11.0 |
The IP Routing feature introduced basic IP routing features that are documented throughout this document and also in other IP Routing Protocol documents. |
NetFlow Policy Routing (NPR) |
12.0(3)T |
NetFlow policy routing (NPR) integrates policy routing, which enables traffic engineering and traffic classification, with NetFlow services, which provide billing, capacity planning, and monitoring information on real-time traffic flows. IP policy routing works with Cisco Express Forwarding (CEF), distributed CEF (dCEF), and NetFlow. The following sections provide information about this feature: |
Policy-Based Routing |
11.0 |
The Policy-Based Routing feature introduced a more flexible mechanism for routing packets than destination routing. Policy-based routing is a process where a router puts packets through a route map before routing the packets. The route map determines which packets are routed to which router next. The following sections provide information about this feature: • The following command was introduced by this feature: ip policy route-map. |
Policy-Based Routing (PBR) Default Next-Hop Route |
12.1(11)E |
The Policy-Based Routing (PBR) Default Next-Hop Route feature introduces the ability for packets that are forwarded as a result of the set ip default next-hop command to be switched at the hardware level. In prior releases, the router packets to be forwarded that are generated from the route map for PBR are switched at the software level. The following sections provide information about this feature: • The following command was modified by this feature: set ip default next-hop. |
Policy Routing Infrastructure |
12.2(15)T |
The Policy Routing Infrastructure feature provides full support of IP policy-based routing in conjunction with Cisco Express Forwarding (CEF) and NetFlow. As CEF gradually obsoletes fast switching, policy routing is integrated with CEF to increase customer performance requirements. When both policy routing and NetFlow are enabled, redundant processing is avoided. The following sections provide information about this feature: |
QoS Policy Propagation via BGP |
12.0 |
The QoS Policy Propagation via BGP feature allows you to classify packets by IP precedence based on BGP community lists, BGP autonomous system paths, and access lists. After a packet has been classified, you can use other QoS features such as committed access rate (CAR) and Weighted Random Early Detection (WRED) to specify and enforce policies to fit your business model. The following sections provide information about this feature: • • • • • |
Feedback