Table Of Contents
Configuring IP Routing Protocol-Independent Features
Protocol-Independent Feature Task List
Using Variable-Length Subnet Masks
Understanding Gateway of Last Resort
Changing the Maximum Number of Paths
Redistributing Routing Information
Understanding Supported Metric Translations
Preventing Routing Updates Through an Interface
Configuring Default Passive Interfaces
Controlling the Advertising of Routes in Routing Updates
Controlling the Processing of Routing Updates
Filtering Sources of Routing Information
Enabling Fast-Switched Policy Routing
Enabling NetFlow Policy Routing
Monitoring and Maintaining the IP Network
Clearing Routes from the IP Routing Table
Displaying System and Network Statistics
IP Routing Protocol-Independent Configuration Examples
Variable-Length Subnet Mask Example
Overriding Static Routes with Dynamic Protocols Example
Administrative Distance Examples
Static Routing Redistribution Example
RIP and IGRP Redistribution Example
RIP and EIGRP Redistribution Examples
OSPF Routing and Route Redistribution Examples
Basic OSPF Configuration Examples
Internal Router, ABR, and ASBRs Configuration Example
Complex OSPF Configuration Example
Default Metric Values Redistribution Example
Default Passive Interface Example
Configuring IP Routing Protocol-Independent Features
This chapter describes how to configure IP routing protocol-independent features. For a complete description of the IP routing protocol-independent commands in this chapter, refer to the "IP Routing Protocol-Independent Commands" chapter of the Cisco IOS IP and IP Routing Command Reference publication. To locate documentation of other commands in this chapter, use the command reference master index or search online.
Protocol-Independent Feature Task List
Previous chapters addressed configurations of specific routing protocols. To configure optional protocol-independent features, perform any of the tasks in the following sections:
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Using Variable-Length Subnet Masks
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See the section "IP Routing Protocol-Independent Configuration Examples" at the end of this chapter for configuration examples.
Using Variable-Length Subnet Masks
Enhanced Interior Gateway Routing Protocol (EIGRP), IS-IS Interdomain Routing Protocol, 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.
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The best way to implement VLSMs is to keep your existing numbering plan in place and gradually migrate some networks to VLSMs to recover address space. See the "Variable-Length Subnet Mask Example" section at the end of this chapter for an example of using VLSMs.
Configuring 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 Cisco IOS software 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 following command in global configuration mode:
ip route prefix mask {address | interface} [distance] [tag tag] [permanent]
Establish a static route.
See the "Overriding Static Routes with Dynamic Protocols Example" section at the end of this chapter for an example of configuring static routes.
The software remembers static routes 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 8. 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, IGRP, and other dynamic routing protocols, regardless of whether redistribute static 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 forwarding router's address in a static route, the static route is removed from the IP routing table.
Specifying 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.
Specifying a 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, it will advertise the pseudonetwork 0.0.0.0. In the case of IGRP, the network itself is advertised and flagged as an exterior 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 following command in global configuration mode:
Understanding 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 IGRP, there might be several networks that can be candidates for the system default. The 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 command. In this usage, ip default-network 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.
Changing the Maximum Number of Paths
By default, most IP routing protocols install a maximum of four parallel routes in a routing table. The exception is BGP, which by default allows only one path to a destination.
The range of maximum paths is one to six paths. To change the maximum number of parallel paths allowed, use the following command in router configuration mode:
maximum-paths maximum
Configure the maximum number of parallel paths allowed in a routing table.
Redistributing Routing Information
In addition to running multiple routing protocols simultaneously, the Cisco IOS software can redistribute information from one routing protocol to another. For example, you can instruct the software to readvertise IGRP-derived routes using the RIP protocol, or to readvertise static routes using the IGRP protocol. Redistributing information from one routing protocol to another applies to all of the IP-based routing protocols.
You also can conditionally control the redistribution of routes between routing domains by defining a method known as route maps between the two domains.
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 following command in global configuration mode:
route-map map-tag [permit | deny] [sequence-number]
Define any route maps needed to control redistribution.
One or more match commands and one or more set commands typically follow a route-map command. If there are no match commands, then everything matches. If there are no set commands, nothing is done (other than the match). Therefore, you need at least one match or set command. 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:
One or more match commands and one or more set commands should follow a route-map command. 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:
See the "BGP Route Map Examples" section in the "Configuring BGP" chapter for examples of BGP route maps. See the "BGP Community with Route Maps Examples" section in the "Configuring BGP" chapter for examples of BGP communities and route maps.
To distribute routes from one routing domain into another and to control route redistribution, use the following commands in router configuration mode:
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 IGRP metric is a combination of five quantities. In such situations, an artificial metric is assigned to the redistributed route. Because of this unavoidable tampering with dynamic information, carelessly exchanging routing information between different routing protocols can create routing loops, which can seriously degrade network operation.
Understanding 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:
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Filtering Routing Information
You can filter routing protocol information by performing the following tasks, each of which is described in this section:
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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. Keep 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 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 following command in router configuration mode:
passive-interface type number
Suppress the sending of routing updates through the specified interface.
See the "Passive Interface Examples" section at the end of this chapter for examples of configuring passive interfaces.
Configuring 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:
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Network managers may not always be able to summarize Type5 link-state advertisements (LSAs) at the router level where redistribution occurs, as in the first possibility. Thus, a large number of Type5 LSAs can be flooded over the domain.
In the second possibility, large Type1 LSAs might be flooded into the area. The Area Border Router (ABR) creates Type3 LSAs, one for each Type1 LSAs, and floods them to the backbone. It is possible, however, to have unique summarization at the ABR level, which will inject just 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 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 need to have adjacencies set, use the following commands beginning in global configuration mode:
See the section "Default Passive Interface Example" at the end of this chapter 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 show ip ospf interface, or you could verify the interfaces you enabled as active using a command such as show ip interface.
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 a particular device's interpretation 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 following 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 following command in router configuration mode:
distribute-list {access-list-number | access-list-name} in [type number]
Suppress routes listed in updates from being processed.
Filtering Sources of Routing Information
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, use the following command in router configuration mode:
distance {ip-address {ip-address mask}} [ip standard list] [ip extended list]
Filter on routing information sources.
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 8 shows the default administrative distance for various routing information sources.
For example, consider a router using IGRP and RIP. Suppose you trust the IGRP-derived routing information more than the RIP-derived routing information. In this example, because the default IGRP administrative distance is lower than the default RIP administrative distance, the router uses the IGRP-derived information and ignores the RIP-derived information. However, if you lose the source of the IGRP-derived information (because of a power shutdown in another building, for example), the router uses the RIP-derived information until the IGRP-derived information reappears.
For an example of filtering on sources of routing information, see the section "Administrative Distance Examples" at the end of this chapter.
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Enabling Policy Routing
Policy 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 routing if you want certain packets to be routed some way other than the obvious shortest path. Some possible applications for policy routing are to provide equal access, protocol-sensitive routing, source-sensitive routing, routing based on interactive versus batch traffic, or routing based on dedicated links.
To enable policy routing, you must identify which route map to use for policy 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 routing on an interface, indicate which route map the router should use by using the following command in interface configuration mode. All packets arriving on the specified interface will be subject to policy routing. This command disables fast switching of all packets arriving on this interface.
To define the route map to be used for policy routing, use the following command in global configuration mode:
route-map map-tag [permit | deny] [sequence-number]
Define a route map to control where packets are output.
The next step is to define the criteria by which packets are examined to learn if they will be policy-routed. No match clause in the route map indicates all packets. Use one or both of the following commands in route-map configuration mode:
The last step is to set the precedence and specify where the packets that pass the match criteria are output. To do so, use the following commands in route-map configuration mode:
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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 it had.
The precedence bits in the IP header can be set in the router when policy 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 first in, first out (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 command to determine precedence. Table 9 lists the possible numbers and their corresponding name, from least important to most important.
Table 9 IP Precedence Values
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routine
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flash
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flash-override
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critical
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internet
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network
The set commands can be used in conjunction 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.
If you want policy routing to be fast-switched, see the following section "Enabling Fast-Switched Policy Routing."
See the "Policy Routing Example" section at the end of this chapter for an example of policy routing.
Enabling Fast-Switched Policy Routing
IP policy routing can now be fast switched. Prior to this feature, 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:
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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 following command in interface configuration mode:
Enabling 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.
ip local policy route-map map-tag
Identify the route map to use for local policy routing.
Use the show ip local policy command to display the route map used for local policy routing, if one exists.
Enabling 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 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:
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Following are NPR benefits:
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Following are NPR restrictions:
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In order for NetFlow policy routing to work, the following features must already be configured:
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To configure CEF, dCEF, or NetFlow, refer to the appropriate chapter of the Cisco IOS Switching Services 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:
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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 will continue forever.
To prevent this situation, you can configure the router to first verify that the next hop(s) of the route map is the CDP neighbor(s) 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 following command in route-map configuration mode:
set ip next-hop verify-availability
Causes the router to confirm that the next hop(s) of the route map is a CDP neighbor(s) of the router.
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 simply are not policy routed.
If the command shown is not set, the packets are either successfully 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 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 "IP Routing Protocol-Independent Commands" chapter of the Cisco IOS IP and IP Routing Command Reference publication for policy routing commands and the appropriate chapter of the Cisco IOS Switching Services Command Reference publication 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 following command in EXEC mode:
Managing Authentication Keys
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 see how to enable authentication for that protocol.
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 number 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 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 Cisco IOS Configuration Fundamentals Configuration Guide.
To manage authentication keys, use the following commands beginning in global configuration mode:
Use the show key chain command to display key chain information. For examples of key management, see the "Key Management Examples" section at the end of this chapter.
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 following command in EXEC mode:
clear ip route {network [mask] | *}
Clear one or more routes from the IP routing table.
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 packets leaving your device are taking through the network.
To display various routing statistics, use the following commands in EXEC mode:
IP Routing Protocol-Independent Configuration Examples
The following sections provide routing protocol-independent configuration examples:
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Variable-Length Subnet Mask Example
In the following example, a 14-bit subnet mask is used, leaving two bits of address space reserved for serial line host addresses. There is sufficient host address space for two host endpoints on a point-to-point serial link.
interface ethernet 0ip address 172.17.1.1 255.255.255.0! 8 bits of host address space reserved for ethernetsinterface serial 0ip address 172.17.254.1 255.255.255.252! 2 bits of address space reserved for serial lines! Router is configured for OSPF and assigned AS 1router ospf 1! Specifies the network directly connected to the routernetwork 172.17.0.0 0.0.255.255 area 0.0.0.0Overriding Static Routes with Dynamic Protocols Example
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 46 illustrates this point. 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.
ip route 10.0.0.0 255.0.0.0 172.18.3.4 110Figure 46 Overriding Static Routes
Administrative Distance Examples
In the following example, the router igrp global configuration command sets up IGRP routing in autonomous system 1. The network router configuration commands specify IGRP 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 90 for all routers on the Class C network 192.168.7.0. The third distance command sets the administrative distance to 120 for the router with the address 172.16.1.3.
router igrp 1network 192.168.7.0network 172.16.0.0distance 255distance 90 192.168.7.0 0.0.0.255distance 120 172.16.1.3 0.0.0.0The 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:
distance 100 192.168.7.18 0.0.0.0distance 200 192.168.7.0 0.0.0.255However, 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:
distance 200 192.168.7.0 0.0.0.255distance 100 192.168.7.18 0.0.0.0Assigning administrative distances is a problem unique to each network and is done in response to the greatest perceived threats to the connected network. Even when general guidelines exist, the network manager must ultimately determine a reasonable matrix of administrative distances for the network as a whole.
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 isisdistance 90 ipStatic Routing Redistribution Example
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 IGRP process. Any redistributed static routes should be sourced by a single router to minimize the likelihood of creating a routing loop.
ip route 192.168.2.0 255.255.255.0 192.168.7.65ip route 192.168.5.0 255.255.255.0 192.168.7.65ip route 172.16.0.0 255.255.255.0 192.168.7.65access-list 3 permit 192.168.2.0access-list 3 permit 192.168.5.0!router igrp 1network 192.168.7.0default-metric 10000 100 255 1 1500redistribute staticdistribute-list 3 out staticIGRP Redistribution Example
Each IGRP routing process can provide routing information to only one autonomous system; the Cisco IOS software must run a separate IGRP process and maintain a separate routing database for each autonomous system that it services. However, you can transfer routing information between these routing databases.
Suppose that the router has one IGRP routing process for network 10.0.0.0 in autonomous system 71 and another IGRP routing process for network 192.168.7.0 in autonomous system 1, as the following commands specify:
router igrp 71network 10.0.0.0router igrp 1network 192.168.7.0To transfer a route to 192.168.7.0 into autonomous system 71 (without passing any other information about autonomous system 1), use the command in the following example:
router igrp 71redistribute igrp 1distribute-list 3 out igrp 1access-list 3 permit 192.168.7.0RIP and IGRP Redistribution Example
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 IGRP 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. The commands for the interconnecting router are listed in the example that follows:
router igrp 1network 172.16.0.0redistribute ripdefault-metric 10000 100 255 1 1500distribute-list 10 out ripIn this example, the router global configuration command starts an IGRP routing process. The network router configuration command specifies that network 172.16.0.0 (the regional network) is to receive IGRP 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 IGRP 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.
EIGRP Redistribution Examples
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.
Suppose that the software has one EIGRP routing process for network 10.0.0.0 in autonomous system 71 and another EIGRP routing process for network 192.168.7.0 in autonomous system 1, as the following commands specify:
router eigrp 71network 10.0.0.0router eigrp 1network 192.168.7.0To transfer a route from 192.168.7.0 into autonomous system 71 (without passing any other information about autonomous system 1), use the command in the following example:
router eigrp 71redistribute eigrp 1 route-map 1-to-71route-map 1-to-71 permitmatch ip address 3set metric 10000 100 1 255 1500access-list 3 permit 192.168.7.0The following example is an alternative way to transfer a route to 192.168.7.0 into autonomous system 71. Unlike the previous configuration, this one does not allow you to arbitrarily set the metric.
router eigrp 71redistribute eigrp 1distribute-list 3 out eigrp 1access-list 3 permit 192.168.7.0RIP and EIGRP Redistribution Examples
This section provides a simple RIP redistribution example and a complex redistribution example between EIGRP and BGP.
Example 1: 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. The commands for the interconnecting router are listed in the example that follows:
router eigrp 1network 172.16.0.0redistribute ripdefault-metric 10000 100 255 1 1500distribute-list 10 out ripIn this example, the router global configuration command starts an EIGRP routing process. 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 2: Complex Redistribution
The most complex redistribution case is one in which mutual redistribution is required between an IGP (in this case EIGRP) and BGP.
Suppose that BGP is running on a router somewhere else in autonomous system 50000 and that the BGP routes are injected into EIGRP routing process 1. You must use filters to ensure that the proper routes are advertised. The example configuration for router R1 illustrates use of access filters and a distribution list to filter routes advertised to BGP neighbors. This example also illustrates configuration commands for redistribution between BGP and EIGRP.
! Configuration for router R1:router bgp 50000network 172.18.0.0neighbor 192.168.10.1 remote-as 2neighbor 192.168.10.15 remote-as 1neighbor 192.168.10.24 remote-as 3redistribute eigrp 1distribute-list 1 out eigrp 1!! All networks that should be advertised from R1 are controlled with access lists:!access-list 1 permit 172.18.0.0access-list 1 permit 172.16.0.0access-list 1 permit 172.17.0.0!router eigrp 1network 172.18.0.0network 192.168.10.0redistribute bgp 50000OSPF Routing and Route Redistribution Examples
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:
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Basic OSPF Configuration Examples
The following example illustrates a simple OSPF configuration that enables OSPF routing process 9000, attaches Ethernet 0 to area 0.0.0.0, and redistributes RIP into OSPF and OSPF into RIP:
interface ethernet 0ip address 172.16.1.1 255.255.255.0ip ospf cost 1!interface ethernet 1ip address 172.17.1.1 255.255.255.0!router ospf 9000network 172.16.0.0 0.0.255.255 area 0.0.0.0redistribute rip metric 1 subnets!router ripnetwork 172.17.0.0redistribute ospf 9000default-metric 1The 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 ospf 1network 172.16.20.0 0.0.0.255 area 10.9.50.0network 172.16.0.0 0.0.255.255 area 2network 172.17.10.0 0.0.0.255 area 3network 0.0.0.0 255.255.255.255 area 0!! Ethernet interface 0 is in area 10.9.50.0:interface ethernet 0ip address 172.16.20.5 255.255.255.0!! Ethernet interface 1 is in area 2:interface ethernet 1ip address 172.16.1.5 255.255.255.0!! Ethernet interface 2 is in area 2:interface ethernet 2ip address 172.17.2.5 255.255.255.0!! Ethernet interface 3 is in area 3:interface ethernet 3ip address 172.18.10.5 255.255.255.0!! Ethernet interface 4 is in area 0:interface ethernet 4ip address 172.19.1.1 255.255.255.0!! Ethernet interface 5 is in area 0:interface ethernet 5ip address 10.1.0.1 255.255.0.0Each 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 "IP Routing Protocols Commands" chapter of the Cisco IOS IP and IP Routing Command Reference publication 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.
Internal Router, ABR, and ASBRs Configuration Example
Figure 47 provides a general network map that illustrates a sample configuration for several routers within a single OSPF autonomous system.
Figure 47 Sample OSPF Autonomous System Network Map
In this configuration, five routers are configured in OSPF autonomous system 1:
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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 sample configuration for the general network map shown in Figure 47.
Router A—Internal Router
interface ethernet 1ip address 192.168.1.1 255.255.255.0router ospf 1network 192.168.1.0 0.0.0.255 area 1Router B—Internal Router
interface ethernet 2ip address 192.168.1.2 255.255.255.0router ospf 1network 192.168.1.0 0.0.0.255 area 1Router C—ABR
interface ethernet 3ip address 192.168.1.3 255.255.255.0interface serial 0ip address 192.168.2.3 255.255.255.0router ospf 1network 192.168.1.0 0.0.0.255 area 1network 192.168.2.0 0.0.0.255 area 0Router D—Internal Router
interface ethernet 4ip address 10.0.0.4 255.0.0.0interface serial 1ip address 192.168.2.4 255.255.255.0router ospf 1network 192.168.2.0 0.0.0.255 area 0network 10.0.0.0 0.255.255.255 area 0Router E—ASBR
interface ethernet 5ip address 10.0.0.5 255.0.0.0interface serial 2ip address 172.16.1.5 255.0.0.0router ospf 1network 10.0.0.0 0.255.255.255 area 0redistribute bgp 50000 metric 1 metric-type 1router bgp 50000network 192.168.0.0network 10.0.0.0neighbor 172.16.1.6 remote-as 60000Complex OSPF Configuration Example
The following example configuration accomplishes several tasks in setting up an ABR. These tasks can be split into two general categories:
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The specific tasks outlined in this configuration are detailed briefly in the following descriptions. Figure 48 illustrates the network address ranges and area assignments for the interfaces.
Figure 48 Interface and Area Specifications for OSPF Example Configuration
The basic configuration tasks in this example are as follows:
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Configuration tasks associated with redistribution are as follows:
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The following is an example OSPF configuration:
interface ethernet 0ip address 192.168.110.201 255.255.255.0ip ospf authentication-key abcdefghip ospf cost 10!interface ethernet 1ip address 172.19.251.201 255.255.255.0ip ospf authentication-key ijklmnopip ospf cost 20ip ospf retransmit-interval 10ip ospf transmit-delay 2ip ospf priority 4!interface ethernet 2ip address 172.19.254.201 255.255.255.0ip ospf authentication-key abcdefghip ospf cost 10!interface ethernet 3ip address 10.0.0.201 255.255.0.0ip ospf authentication-key ijklmnopip ospf cost 20ip ospf dead-interval 80OSPF is on network 172.19.0.0:
router ospf 1network 10.0.0.0 0.255.255.255 area 10.0.0.0network 192.168.110.0 0.0.0.255 area 192.1682.110.0network 172.19.0.0 0.0.255.255 area 0area 0 authenticationarea 10.0.0.0 stubarea 10.0.0.0 authenticationarea 10.0.0.0 default-cost 20area 192.168.110.0 authenticationarea 10.0.0.0 range 10.0.0.0 255.0.0.0area 192.168.110.0 range 192.168.110.0 255.255.255.0area 0 range 172.19.251.0 255.255.255.0area 0 range 172.19.254.0 255.255.255.0redistribute igrp 200 metric-type 2 metric 1 tag 200 subnetsredistribute rip metric-type 2 metric 1 tag 200IGRP autonomous system 1 is on 172.19.0.0:
router igrp 1network 172.19.0.0!! RIP for 192.168.110.0!router ripnetwork 192.168.110.0redistribute igrp 1 metric 1redistribute ospf 201 metric 1Default Metric Values Redistribution Example
The following example shows a router in autonomous system 1 using both RIP and IGRP. The example advertises IGRP-derived routes using the RIP protocol and assigns the IGRP-derived routes a RIP metric of 10.
router ripdefault-metric 10redistribute igrp 1Route Map Examples
The examples in this section illustrate the use of redistribution, with and without route maps. Examples from both the IP and CLNS routing protocols are given.
The following example redistributes all OSPF routes into IGRP:
router igrp 1redistribute ospf 110The 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 type of Type 1, and a tag equal to 1.
router ospf 1redistribute rip route-map rip-to-ospf!route-map rip-to-ospf permitmatch metric 1set metric 5set metric-type type1set tag 1The following example redistributes OSPF learned routes with tag 7 as a RIP metric of 15:
router ripredistribute ospf 1 route-map 5!route-map 5 permitmatch tag 7set metric 15The 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 bgp 50000redistribute ospf 1 route-map 10!route-map 10 permitmatch route-type internalmatch interface serial 0set metric 5The following example redistributes two types of routes into the integrated IS-IS routing table (supporting both IP and Connectionless Network Service [CLNS]). The first are OSPF external IP routes with tag 5; these are inserted into Level 2 IS-IS link-state packets (LSPs) with a metric of 5. The second are ISO-IGRP derived CLNS prefix routes that match CLNS access list 2000. These will be redistributed into IS-IS as Level 2 LSPs with a metric of 30.
router isisredistribute ospf 1 route-map 2redistribute iso-igrp nsfnet route-map 3 !route-map 2 permitmatch route-type externalmatch tag 5set metric 5set level level-2!route-map 3 permitmatch address 2000set metric 30With 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 ripredistribute ospf 1 route-map 1!route-map 1 permitmatch tag 1 2set metric 1!route-map 1 permitmatch tag 3set metric 5!route-map 1 denymatch tag 4!route map 1 permitmatch tag 5set metric 5Given 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 isisredistribute rip route-map 1redistribute iso-igrp remote route-map 1!route-map 1 permitmatch ip address 1match clns address 2set metric 5set level level-2!access-list 1 permit 172.18.0.0 0.0.255.255clns 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. Extended access lists cannot be used in a route map for conditional default origination.
route-map ospf-default permitmatch ip address 1set metric 5set metric-type type-2!access-list 1 172.20.0.0 0.0.255.255!router ospf 1default-information originate route-map ospf-defaultSee more route map examples in the "BGP Route Map Examples" "BGP Community with Route Maps Examples" sections of the "Configuring BGP" chapter.
Passive Interface Examples
The following example configures Ethernet interface 1 as a passive interface under IGRP. Figure 49 shows the router topology. Routing updates are sent out all interfaces in the 192.168/16 network except for Ethernet interface 1.
interface Ethernet 1ip address 192.168.0.1 255.255.0.0router igrp 1network 192.168.0.0passive-interface ethernet 1Figure 49 Filtering IGRP Updates
In the following example, as in the first example, IGRP updates are sent out all interfaces in the 192.168/16 network except for Ethernet interface 1. However, in this configuration a neighbor statement is configured explicitly for the 192.168.0.2 neighbor. This neighbor statement will override the passive-interface configuration, and all interfaces in the 192.168/16 network, including Ethernet interface 1, will send routing advertisements to the 192.168.0.2 neighbor.
router igrp 1network 192.168.0.0passive-interface ethernet 1neighbor 192.168.0.2The passive-interface command disables the transmission and receipt of EIGRP hello packets on an interface. Unlike IGRP or RIP, EIGRP sends hello packets in order to form and sustain neighbor adjacencies. Without a neighbor adjacency, EIGRP cannot exchange routes with a neighbor. Therefore, the passive-interface command prevents the exchange of routes on the interface. Although EIGRP does not send or receive routing updates on an interface configured with the passive-interface command, it still includes the address of the interface in routing updates sent out of other nonpassive interfaces.
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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 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:
interface ethernet 0ip address 172.18.1.1 255.255.255.0interface ethernet 1ip address 172.18.2.1 255.255.255.0interface ethernet 2ip address 172.18.3.1 255.255.255.0!router ospf 1network 172.18.0.0 0.0.255.255 area 0If you do not want OSPF to run on 172.18.3.0, enter the following commands:
router ospf 1network 172.18.0.0 0.0.255.255 area 0passive-interface ethernet 2Default Passive Interface Example
The following example configures the network interfaces, sets all interfaces that are running OSPF as passive, and then enables serial interface 0:
interface Ethernet0ip address 172.19.64.38 255.255.255.0 secondaryip address 172.19.232.70 255.255.255.240no ip directed-broadcast!interface Serial0ip address 172.24.101.14 255.255.255.252no ip directed-broadcastno ip mroute-cache!interface TokenRing0ip address 172.20.10.4 255.255.255.0no ip directed-broadcastno ip mroute-cachering-speed 16!router ospf 1passive-interface defaultno passive-interface Serial0network 172.16.10.0 0.0.0.255 area 0network 172.19.232.0 0.0.0.255 area 4network 172.24.101.0 0.0.0.255 area 4Policy Routing Example
The following example provides two sources with equal access to two different service providers. Packets that arrive on async 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.
access-list 1 permit ip 10.1.1.1access-list 2 permit ip 172.17.2.2!interface async 1ip policy route-map equal-access!route-map equal-access permit 10match ip address 1set ip default next-hop 172.16.6.6route-map equal-access permit 20match ip address 2set ip default next-hop 192.168.7.7route-map equal-access permit 30set default interface null0CEF Policy Routing Example
The following example configures policy routing with CEF. It also configures policy routing to verify that next hop 10.0.0.8 of route map test is a CDP neighbor before the router tries to policy-route to it.
If the first packet is being policy-routed via route map test sequence 10, the subsequent packets of the same flow always take the same route map test sequence 10, not route map test sequence 20, because they all match or pass the access list 1 check.
ip cefinterface ethernet0/0/1ip route-cache flowip policy route-map testroute-map test permit 10match ip address 1set ip precedence priorityset ip next-hop 10.0.0.8set ip next-hop verify-availabilityroute-map test permit 20match ip address 101set interface Ethernet0/0/3set ip tos max-throughputKey Management Examples
The following example configures a key chain called 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 discrepancies in the router's time-of-day. Likewise, the key birch immediately follows chestnut, and there is a half-hour leeway on each side to handle time-of-day differences.
interface ethernet 0ip rip authentication key-chain treesip rip authentication mode md5!router ripnetwork 172.19.0.0version 2!key chain treeskey 1key-string willowkey 2key-string chestnutaccept-lifetime 13:30:00 Jan 25 1996 duration 7200send-lifetime 14:00:00 Jan 25 1996 duration 3600key 3key-string birchaccept-lifetime 14:30:00 Jan 25 1996 duration 7200send-lifetime 15:00:00 Jan 25 1996 duration 3600The following example configures a key chain called trees:
key chain treeskey 1key-string willowkey 2key-string chestnutaccept-lifetime 00:00:00 Dec 5 1995 23:59:59 Dec 5 1995send-lifetime 06:00:00 Dec 5 1995 18:00:00 Dec 5 1995!interface Ethernet0ip address 172.19.104.75 255.255.255.0 secondaryip address 172.16.232.147 255.255.255.240ip rip authentication key-chain treesmedia-type 10BaseT!interface Ethernet1no ip addressshutdownmedia-type 10BaseTinterface Fddi0ip address 10.1.1.1 255.255.255.0no keepalive!interface Fddi1ip address 172.16.1.1 255.255.255.0ip rip send version 1ip rip receive version 1no keepalive!router ripversion 2network 172.19.0.0network 10.0.0.0network 172.16.0.0
