IP Routing: Protocol-Independent Configuration Guide, Cisco IOS XE Release 3S
Basic IP Routing
Downloads: This chapterpdf (PDF - 1.66MB) The complete bookPDF (PDF - 3.85MB) | Feedback

Contents

Basic IP Routing

This module describes how to configure basic IP routing. The Internet Protocol (IP) is a network layer (Layer 3) protocol that contains addressing information and some control information that enables packets to be routed. IP is documented in RFC 791 and is the primary network layer protocol in the Internet protocol suite.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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 table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Information About Basic IP Routing

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 that the network is more difficult to monitor using VLSMs.


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.

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 device 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] global configuration command.

Static routes remains in the device configuration until you remove them (using the no ip route global configuration command). However, you can override static routes with dynamic routing information through prudent assignment of administrative distance values. An administrative distance is a rating of the trustworthiness of a routing information source, such as an individual router or a group of routers. Numerically, an administrative distance is an integer from 0 to 255. In general, the higher the value, the lower the trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored.

Each dynamic routing protocol has a default administrative distance, as listed in the table below. If you want 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.

Table 1 Default Administrative Distances for Dynamic Routing Protocols

Route Source

Default Distance

Connected interface

0

Static route

1

Enhanced Interior Gateway Routing Protocol (EIGRP) summary route

5

External Border Gateway Protocol (BGP)

20

Internal EIGRP

90

Interior Gateway Routing Protocol (IGRP)

100

Open Shortest Path First (OSPF)

110

intermediate System to Intermediate System (IS-IS)

115

Routing Information Protocol (RIP)

120

Exterior Gateway Routing Protocol (EGP)

140

On Demand Routing (ODR)

160

External EIGRP

170

Internal BGP

200

Unknown

255

Static routes that point to an interface are advertised via RIP, EIGRP, and other dynamic routing protocols, regardless of whether redistribute static router configuration commands are 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 device in a static route, the static route is removed from the IP routing table.


Note


A packet with an E-class source address (240.0.0.0/4) gets dropped on Cisco ASR 1000 Series Aggregation Services Routers, although RFC 1812 (Requirements for IP Version 4 Routers) defines this behavior only for destination addresses and not specifically for source addresses.


Default Routes

Default routes, also known as gateways of last resort, are used to route packets that are addressed to networks not explicitly listed in the routing table. A device might not be able to determine routes to all networks. To provide complete routing capability, network administrators use some devices as smart devices and give the remaining devices default routes to the smart device. (Smart devices have routing table information for the entire internetwork.) Default routes can be either passed along dynamically or configured manually into individual devices.

Most dynamic interior routing protocols include a mechanism for causing a smart device to generate dynamic default information, which is then passed along to other devices.

You can configure a default route by using the following commands:
  • ip default-gateway
  • ip default-network
  • ip route 0.0.0.0 0.0.0.0

You can use the ip default-gateway global configuration command to define a default gateway when IP routing is disabled on a device. For instance, if a device is a host, you can use this command to define a default gateway for the device. You can also use this command to transfer a Cisco software image to a device when the device is in boot mode. In boot mode, IP routing is not enabled on the device.

Unlike the ip default-gateway command, the ip default-network command can be used when IP routing is enabled on a device. When you specify a network by using the ip default-network command, the device considers routes to that network for installation as the gateway of last resort on the device.

Gateways of last resort configured by using the ip default-network command are propagated differently depending on which routing protocol is propagating the default route. For Interior Gateway Routing Protocol (IGRP) and Enhanced Interior Gateway Routing Protocol (EIGRP) to propagate the default route, the network specified by the ip default-network command must be known to IGRP or EIGRP. The network must be an IGRP- or EIGRP-derived network in the routing table, or the static route used to generate the route to the network must be redistributed into IGRP or EIGRP or advertised into these protocols by using the network command. The Routing Information Protocol (RIP) advertises a route to network 0.0.0.0 if a gateway of last resort is configured by using the ip default-network command. The network specified in the ip default-network command need not be explicitly advertised under RIP.

Creating a static route to network 0.0.0.0 0.0.0.0 by using the ip route 0.0.0.0 0.0.0.0 command is another way to set the gateway of last resort on a device. As with the ip default-network command, using the static route to 0.0.0.0 is not dependent on any routing protocols. However, IP routing must be enabled on the device. IGRP does not recognize a route to network 0.0.0.0. Therefore, it cannot propagate default routes created by using the ip route 0.0.0.0 0.0.0.0 command. Use the ip default-network command to have IGRP propagate a default route.

EIGRP propagates a route to network 0.0.0.0, but the static route must be redistributed into the routing protocol.

Depending on your release of the Cisco software, the default route created by using the ip route 0.0.0.0 0.0.0.0 command is automatically advertised by RIP devices. In some releases, RIP does not advertise the default route if the route is not learned via RIP. You might have to redistribute the route into RIP by using the redistribute command.

Default routes created using the ip route 0.0.0.0 0.0.0.0 command are not propagated by Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (IS-IS). Additionally, these default routes cannot be redistributed into OSPF or IS-IS by using the redistribute command. Use the default-information originate command to generate a default route into an OSPF or IS-IS routing domain.

Default Network

Default networks are used to route packets to destinations not established in the routing table. You can use the ip default-network network-number global configuration command to configure a default network when IP routing is enabled on the device. When you configure a default network, the device considers routes to that network for installation as the gateway of last resort on the device.

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 the Routing Information Protocol (RIP), there is only one choice, network 0.0.0.0. In the case of Enhanced Interior Gateway Routing Protocol (EIGRP), there might be several networks that can be candidates for the system default. Cisco 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 privileged 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 device 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 Border Gateway Protocol (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.

The number of parallel routes that you can configure to be installed in the routing table is dependent on the installed version of Cisco 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 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.

Routing Information Redistribution

In addition to running multiple routing protocols simultaneously, Cisco software can be configured to redistribute information from one routing protocol to another. For example, you can configure a device to readvertise Enhanced Interior Gateway Routing Protocol (EIGRP)-derived routes using the Routing Information Protocol (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.

Although redistribution is a protocol-independent feature, some of the match and set commands are specific to a particular protocol.

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 a route map for redistribution, use the route-map map-tag [permit | deny] [sequence-number] global configuration command.

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 with inbound filtering to avoid routing loops.

Removing options that you have configured for the redistribute command requires careful use of the no 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:

  • The Routing Information Protocol (RIP) can automatically redistribute static routes. It assigns static routes a metric of 1 (directly connected).
  • The Border Gateway Protocol (BGP) does not normally send metrics in its routing updates.
  • The Enhanced Interior Gateway Routing Protocol (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


Note that any protocol can redistribute routes from other routing protocols as long as a default metric is configured.


Protocol Differences in Implementing the no redistribute Command


Caution


Removing options that you have configured for the redistribute command requires careful use of the no redistribute command to ensure that you obtain the result that you are expecting. In most cases, changing or disabling any keyword will not affect the state of other keywords.


Different protocols implement the no redistribute command differently as follows:

  • In Border Gateway Protocol (BGP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP) configurations, the no redistribute command removes only the specified keywords from the redistribute commands in the running configuration. They use the subtractive keyword method when redistributing from other protocols. For example, in the case of BGP, if you configure no redistribute static route-map interior, only the route map is removed from the redistribution, leaving redistribute static in place with no filter.
  • The no redistribute isis command removes the Intermediate System to Intermediate System (IS-IS) redistribution from the running configuration. IS-IS removes the entire command, regardless of whether IS-IS is the redistributed or redistributing protocol.
  • The Enhanced Interior Gateway Routing Protocol (EIGRP) used the subtractive keyword method prior to EIGRP component version rel5. Starting with EIGRP component version rel5, the no redistribute command removes the entire redistribute command when redistributing from any other protocol.

Sources of Routing Information Filtering

Filtering sources of routing information prioritizes routing information from different sources because some pieces of routing information might be more accurate than others. An administrative distance is a rating of the trustworthiness of a routing information source, such as an individual device or a group of devices. In a large network, some routing protocols and some devices can be more reliable than others as sources of routing information. Also, when multiple routing processes are running in the same device for IP, the same route could be advertised by more than one routing process. By specifying administrative distance values, you enable the device to intelligently discriminate between sources of routing information. The device always picks the route whose routing protocol has the lowest administrative distance.

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.

For example, consider a device using the Enhanced Interior Gateway Routing Protocol (EIGRP) and the Routing Information Protocol (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 device 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 device uses the RIP-derived information until the EIGRP-derived information reappears.


Note


You can also use administrative distance to rate the routing information from devices 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.


Authentication Key Management and Supported Protocols

Key management is a method of controlling the authentication keys used by routing protocols. Not all protocols support key management. Authentication keys are available for Director Response Protocol (DRP) Agent, Enhanced Interior Gateway Routing Protocol (EIGRP), and Routing Information Protocol (RIP) Version 2.

You can manage authentication keys by defining key chains, identifying the keys that belong to the key chain, and specifying how long each key is valid. Each key has its own key identifier (specified using the 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 the message digest algorithm 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 ascending order and uses the first valid key it encounters. The lifetimes allow for overlap during key changes.

How to Configure Basic IP Routing

Redistributing Routing Information

You can redistribute routes from one routing domain into another, with or without controlling the redistribution with a route map. To control which routes are redistributed, configure a route map and reference the route map from the redistribute command.

The tasks in this section describe how to define the conditions for redistributing routes (a route map), how to redistribute routes, and how to remove options for redistributing routes, depending on the protocol being used.

Defining Conditions for Redistributing Routes

Route maps can be used to control route redistribution (or to implement policy-based routing). To define conditions for redistributing routes from one routing protocol into another, configure the route-map command. Then use at least one match command in route map configuration mode, as needed. At least one match command is used in this task because the purpose of the task is to illustrate how to define one or more conditions on which to base redistribution.


Note


A route map is not required to have match commands; it can have only set commands. If there are no match commands, everything matches the route map.



Note


There are many more match commands not shown in this table. For additional match commands, see the Cisco IOS Master Command List.


Command or Action

Purpose

match as-path path-list-number 

Matches a BGP autonomous system path access list.

match community {standard-list-number | expanded-list-number | community-list-name match community[exact]} 

Matches a BGP community.

match ip address {access-list-number [access-list-number... | access-list-name...] | access-list-name [access-list-number...| access-list-name] | prefix-list prefix-list-name [prefix-list-name...]} 

Matches routes that have a destination network address that is permitted to policy route packets or is permitted by a standard access list, an extended access list, or a prefix list.

match metric metric-value

Matches routes with the specified metric.

match ip next-hop {access-list-number | access-list-name} [access-list-number | access-list-name]

Matches a next-hop device address passed by one of the specified access lists.

match tag tag-value [tag-value]

Matches the specified tag value.

match interface type number [type number]

Matches routes that use the specified interface as the next hop.

match ip route-source {access-list-number | access-list-name} [access-list-number | access-list-name]

Matches the address specified by the advertised access lists.

match route-type {local | internal | external [type-1 | type-2] | level-1 | level-2}

Matches the specified route type.

To optionally specify the routing actions for the system to perform if the match criteria are met (for routes that are being redistributed by the route map), use one or more set commands in route map configuration mode, as needed.


Note


A route map is not required to have set commands; it can have only match commands.



Note


There are more set commands not shown in this table. For additional set commands, see the Cisco IOS Master Command List.


Command or Action

Purpose

set community {community-number [additive] [well-known]| none} 

Sets the community attribute (for BGP).

set dampening halflife reuse suppress max-suppress-time

Sets route dampening parameters (for BGP).

set local-preference number-value

Assigns a local preference value to a path (for BGP).

set origin {igp | egp as-number | incomplete} 

Sets the route origin code.

set as-path{tag | prepend as-path-string } 

Modifies the autonomous system path (for BGP).

set next-hop next-hop

Specifies the address of the next hop.

set automatic-tag

Enables automatic computation of the tag table.

set level {level-1 | level-2 | level-1-2 | stub-area | backbone}

Specifies the areas to import routes.

set metric metric-value

Sets the metric value for redistributed routes (for any protocol, except EIGRP).

set metric bandwidth delay reliability load mtu

Sets the metric value for redistributed routes (for EIGRP only).

set metric-type {internal | external | type-1 | type-2}

Sets the metric type for redistributed routes.

set metric-type internal 

Sets the Multi Exit Discriminator (MED) value on prefixes advertised to the external BGP neighbor to match the Interior Gateway Protocol (IGP) metric of the next hop.

set tag tag-value

Sets a tag value to be applied to redistributed routes.

Redistributing Routes from One Routing Domain to Another

Perform this task to redistribute routes from one routing domain into another and to control route redistribution. This task shows how to redistribute OSPF routes into a BGP domain.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    router bgp autonomous-system

    4.    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]

    5.    default-metric number

    6.    end


DETAILED STEPS
      Command or Action Purpose
    Step 1 enable


    Example:
    Device> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2 configure terminal


    Example:
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3 router bgp autonomous-system


    Example:
    Device(config)# router bgp 109
     

    Enables a BGP routing process and enters router configuration mode.

     
    Step 4 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]


    Example:
    Device(config-router)# redistribute ospf 2 level-1       
    
     

    Redistributes routes from the specified routing domain into another routing domain.

     
    Step 5 default-metric number


    Example:
    Device(config-router)# default-metric 10        
    
     

    Sets the default metric value for redistributed routes.

    Note   

    The metric value specified in the redistribute command supersedes the metric value specified using the default-metric command.

     
    Step 6 end


    Example:
    Device(config-router)# end        
    
     

    Exits router configuration mode and returns to privileged EXEC mode.

     

    Removing Options for Redistribution Routes


    Caution


    Removing options that you have configured for the redistribute command requires careful use of the no redistribute command to ensure that you obtain the result that you are expecting.


    Different protocols implement the no redistribute command differently as follows:

    • In BGP, OSPF, and RIP configurations, the no redistribute command removes only the specified keywords from the redistribute commands in the running configuration. They use the subtractive keyword method when redistributing from other protocols. For example, in the case of BGP, if you configure no redistribute static route-map interior, only the route map is removed from the redistribution, leaving redistribute static in place with no filter.
    • The no redistribute isis command removes the IS-IS redistribution from the running configuration. IS-IS removes the entire command, regardless of whether IS-IS is the redistributed or redistributing protocol.
    • EIGRP used the subtractive keyword method prior to EIGRP component version rel5. Starting with EIGRP component version rel5, the no redistribute command removes the entire redistribute command when redistributing from any other protocol.
    • For the no redistribute connected command, the behavior is subtractive if the redistribute command is configured under the router bgp or the router ospf command. The behavior is complete removal of the command if it is configured under the router isis or the router eigrp command.

    The following OSPF commands illustrate how various options are removed from the redistribution in router configuration mode.

    Command or Action

    Purpose

    no redistribute connected metric 1000 subnets

    Removes the configured metric value of 1000 and the configured subnets and retains the redistribute connected command in the configuration.

    no redistribute connected metric 1000 

    Removes the configured metric value of 1000 and retains the redistribute connected subnets command in the configuration.

    no redistribute connected subnets 

    Removes the configured subnets and retains the redistribute connected metric metric-value command in the configuration.

    no redistribute connected 

    Removes the redistribute connected command and any of the options that were configured for the command.

    Configuring Routing Information Filtering


    Note


    When routes are redistributed between Open Shortest Path First (OSPF) processes, no OSPF metrics are preserved.


    Controlling the Advertising of Routes in Routing Updates

    To prevent other devices from learning one or more routes, you can suppress routes from being advertised in routing updates. 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.

    You cannot specify an interface name in Open Shortest Path First (OSPF). When used for OSPF, this feature applies only to external routes.

    Controlling the Processing of Routing Updates

    You might want to avoid processing certain routes that are listed in incoming updates (this does not apply to Open Shortest Path First [OSPF] or Intermediate System to Intermediate System [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.

    Managing Authentication Keys

    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
        Command or Action Purpose
      Step 1 enable


      Example:

      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 ascending order and uses the first valid key it encounters. The lifetimes allow for overlap during key changes.

      Device> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.
       
      Step 2 configure terminal


      Example:
      Device# configure terminal
       

      Enters global configuration mode.

       
      Step 3 key chain name-of-chain


      Example:
      Device(config)# key chain chain1
       

      Defines a key chain and enters key-chain configuration mode.

       
      Step 4 key number


      Example:
      Device(config-keychain)# key key1
       

      Identifies the key number in key-chain configuration mode and enters key-chain key configuration mode.

       
      Step 5 key-string text


      Example:
      Device(config-keychain-key)# key-string string1
       

      Identifies the key string.

       
      Step 6 accept-lifetime start-time {infinite | end-time | duration seconds}


      Example:
      Device(config-keychain-key)# accept-lifetime 13:30:00 Dec 22 2011 duration 7200
       

      Specifies the time period during which the key can be received.

       
      Step 7 send-lifetime start-time {infinite | end-time | duration seconds}


      Example:
      Device(config-keychain-key)# send-lifetime 14:30:00 Dec 22 2011 duration 3600
       

      Specifies the time period during which the key can be sent.

       
      Step 8 end


      Example:
      Device(config-keychain-key)# end
       

      Exits key-chain key configuration mode and returns to privileged EXEC mode.

       
      Step 9 show key chain


      Example:
      Device# show key chain
       

      (Optional) Displays authentication key information.

       

      Monitoring and Maintaining the IP Network

      Clearing Routes from the IP Routing Table

      You can remove all contents of a particular table. Clearing a table may 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 privileged EXEC mode.

      Displaying System and Network Statistics

      You can use the following show commands to display system and network statistics. You can display specific statistics such as contents of IP routing tables, caches, and databases. You can also display information about node reachability and discover the routing path that packets leaving your device are taking through the network. This information can an be used to determine resource utilization and solve network problems.

      Command or Action

      Purpose

      show ip cache policy

      Displays cache entries in the policy route cache.

      show ip local policy

      Displays the local policy route map if one exists.

      show ip policy

      Displays policy route maps.

      show ip protocols

      Displays the parameters and current state of the active routing protocols.

       
      show ip route [ip-address [mask] [longer-prefixes] | protocol [process-id] | list {access-list-number | access-list-name} | static download]

      Displays the current state of the routing table.

      show ip route summary

      Displays the current state of the routing table in summary form.

      show ip route supernets-only

      Displays supernets.

      show key chain [name-of-chain]

      Displays authentication key information.

      show route-map [map-name]

      Displays all route maps configured or only the one specified.

      Configuration Examples for Basic IP Routing

      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 265 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 to 172.16.255.252) with 2 host addresses on each subnet.

      Caution: To ensure unambiguous routing, you must not assign 172.16.255.0/24 to a LAN interface in your network.

      Device(config)# interface GigabitEthernet 0/0/0
      Device(config-if)# ip address 172.16.1.1 255.255.255.0
      Device(config-if)# ! 8 bits of host address space reserved for GigabitEthernet interfaces 
      Device(config-if)# exit
      Device(config)# interface Serial 0/0/0
      Device(config-if)# ip address 172.16.255.5 255.255.255.252
      Device(config-if)# ! 2 bits of address space reserved for point-to-point serial interfaces
      Device(config-if)# exit
      Device(config)# router rip 
      Device(config-router)# network 172.16.0.0
      Device(config-router)# ! Specifies the network directly connected to the device 
      

      Example: Overriding Static Routes with Dynamic Protocols

      In the following example, packets for network 10.0.0.0 from Device 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. The figure below illustrates this example. The route learned by a protocol with an administrative distance of less than 110 might cause Device B to send traffic destined for network 10.0.0.0 via the alternate path through Device D.

      Device(config)# ip route 10.0.0.0 255.0.0.0 172.18.3.4 110
      
      Figure 1. Overriding Static Routes

      Example: IP Default Gateway as a Static IP Next Hop When IP Routing Is Disabled

      The following example shows how to configure IP address 172.16.5.4 as the default route when IP routing is disabled:

      Device> enable
      Device# configure terminal
      Device(conf)# no ip routing
      Device(conf)# ip default-gateway 172.16.15.4

      Examples: Administrative Distances

      In the following example, the router eigrp global configuration command configures Enhanced Interior Gateway Routing Protocol (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 device to ignore all routing updates from devices 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 device with the address 172.16.1.3.

      Device(config)# router eigrp 1 
      Device(config-router)# network 192.168.7.0 
      Device(config-router)# network 172.16.0.0 
      Device(config-router)# distance 255 
      Device(config-router)# distance eigrp 80 100 
      Device(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 device with the address 192.168.7.18 an administrative distance of 100 and all other devices on subnet 192.168.7.0 an administrative distance of 200:

      Device(config-router)# distance 100 192.168.7.18 0.0.0.0 
      Device(config-router)# distance 200 192.168.7.0 0.0.0.255 
      

      However, if you reverse the order of these two commands, all devices on subnet 192.168.7.0 are assigned an administrative distance of 200, including the device at address 192.168.7.18:

      Device(config-router)# distance 200 192.168.7.0 0.0.0.255 
      Device(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.

      Device(config)# router isis 
      Device(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 Enhanced Interior Gateway Routing Protocol (EIGRP) process. Any redistributed static routes should be sourced by a single device to minimize the likelihood of creating a routing loop.

      Device(config)# ip route 192.168.2.0 255.255.255.0 192.168.7.65 
      Device(config)# ip route 192.168.5.0 255.255.255.0 192.168.7.65 
      Device(config)# ip route 10.10.10.0 255.255.255.0 10.20.1.2 
      Device(config)# ! 
      Device(config)# access-list 3 permit 192.168.2.0 0.0.255.255 
      Device(config)# access-list 3 permit 192.168.5.0 0.0.255.255 
      Device(config)# access-list 3 permit 10.10.10.0 0.0.0.255 
      Device(config)# ! 
      Device(config)# router eigrp 1 
      Device(config-router)# network 192.168.0.0 
      Device(config-router)# network 10.10.10.0 
      Device(config-router)# redistribute static metric 10000 100 255 1 1500
      Device(config-router)# distribute-list 3 out static
      

      Examples: EIGRP Redistribution

      Each Enhanced Interior Gateway Routing Protocol (EIGRP) routing process provides routing information to only one autonomous system. The Cisco 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:

      Device(config)# router eigrp 1 
      Device(config-router)# network 10.0.0.0 
      Device(config-router)# exit 
      Device(config)# router eigrp 101 
      Device(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):

      Device(config)# access-list 3 permit 192.168.7.0 
      Device(config)# ! 
      Device(config)# route-map 101-to-1 permit 10 
      Device(config-route-map)# match ip address 3 
      Device(config-route-map)# set metric 10000 100 1 255 1500 
      Device(config-route-map)# exit 
      Device(config)# router eigrp 1 
      Device(config-router)# redistribute eigrp 101 route-map 101-to-1 
      Device(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.

      Device(config)# access-list 3 permit 192.168.7.0 
      Device(config)# ! 
      Device(config)# router eigrp 1 
      Device(config-router)# redistribute eigrp 101 
      Device(config-router)# distribute-list 3 out eigrp 101 
      Device(config-router)# !
      

      Example: Mutual Redistribution Between EIGRP and RIP

      Consider a WAN at a university that uses the Routing Information Protocol (RIP) as an interior routing protocol. Assume that the university wants to connect its WAN to regional network 172.16.0.0, which uses the Enhanced Interior Gateway Routing Protocol (EIGRP) as the routing protocol. The goal in this case is to advertise the networks in the university network to devices in the regional network.

      Mutual redistribution is configured between EIGRP and RIP in the following example:

      Device(config)# access-list 10 permit 172.16.0.0 
      Device(config)# ! 
      Device(config)# router eigrp 1 
      Device(config-router)# network 172.16.0.0 
      Device(config-router)# redistribute rip metric 10000 100 255 1 1500 
      Device(config-router)# default-metric 10
      Device(config-router)# distribute-list 10 out rip 
      Device(config-router)# exit
      Device(config)# router rip 
      Device(config-router)# redistribute eigrp 1 
      Device(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 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 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: Mutual Redistribution Between EIGRP and BGP

      In the following example, mutual redistribution is configured between the Enhanced Interior Gateway Routing Protocol (EIGRP) and the Border Gateway Protocol (BGP).

      Routes from EIGRP routing process 101 are injected into BGP autonomous system 50000. A filter is configured to ensure that the correct routes are advertised, in this case, three networks. Routes from BGP autonomous system 50000 are injected into EIGRP routing process 101. The same filter is used.

      Device(config)# ! All networks that should be advertised from R1 are controlled with ACLs: 
      Device(config)# access-list 1 permit 172.18.0.0 0.0.255.255 
      Device(config)# access-list 1 permit 172.16.0.0 0.0.255.255 
      Device(config)# access-list 1 permit 172.25.0.0 0.0.255.255
      Device(config)# ! Configuration for router R1:
      Device(config)# router bgp 50000 
      Device(config-router)# network 172.18.0.0 
      Device(config-router)# network 172.16.0.0 
      Device(config-router)# neighbor 192.168.10.1 remote-as 2 
      Device(config-router)# neighbor 192.168.10.15 remote-as 1 
      Device(config-router)# neighbor 192.168.10.24 remote-as 3 
      Device(config-router)# redistribute eigrp 101 
      Device(config-router)# distribute-list 1 out eigrp 101 
      Device(config-router)# exit 
      Device(config)# router eigrp 101 
      Device(config-router)# network 172.25.0.0
      Device(config-router)# redistribute bgp 50000 
      Device(config-router)# distribute-list 1 out bgp 50000 
      Device(config-router)# ! 

      Caution


      BGP should be redistributed into an Interior Gateway Protocol (IGP) when there are no other suitable options. Redistribution from BGP into any IGP should be applied with proper filtering by using distribute lists, IP prefix lists, and route map statements to limit the number of prefixes.


      Examples: OSPF Routing and Route Redistribution

      OSPF typically requires coordination among many internal devices, area border routers (ABRs), and Autonomous System Boundary Routers (ASBRs). At a minimum, OSPF-based devices can be configured with all default parameter values, with no authentication, and with interfaces assigned to areas.

      This section provides the following configuration examples:

      • The first example shows simple configurations illustrating basic OSPF commands.
      • The second example shows configurations for an internal device, ABR, and ASBR 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 Gigabit Ethernet interface 0/0/0 to area 0.0.0.0, and redistributes RIP into OSPF and OSPF into RIP:

      Device(config)# interface GigabitEthernet 0/0/0 
      Device(config-if)# ip address 172.16.1.1 255.255.255.0 
      Device(config-if)# ip ospf cost 1 
      Device(config-if)# exit 
      Device(config)# interface GigabitEthernet 1/0/0 
      Device(config-if)# ip address 172.17.1.1 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# router ospf 1 
      Device(config-router)# network 172.18.0.0 0.0.255.255 area 0.0.0.0 
      Device(config-router)# redistribute rip metric 1 subnets 
      Device(config-router)# exit 
      Device(config)# router rip 
      Device(config-router)# network 172.17.0.0 
      Device(config-router)# redistribute ospf 1 
      Device(config-router)# default-metric 1 
      Device(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.

      Device(config)# router ospf 1 
      Device(config-router)# network 172.18.20.0 0.0.0.255 area 10.9.50.0 
      Device(config-router)# network 172.18.0.0 0.0.255.255 area 2 
      Device(config-router)# network 172.19.10.0 0.0.0.255 area 3 
      Device(config-router)# network 0.0.0.0 255.255.255.255 area 0 
      Device(config-router)# exit 
      Device(config)# ! GigabitEthernet interface 0/0/0 is in area 10.9.50.0:
      Device(config)# interface GigabitEthernet 0/0/0 
      Device(config-if)# ip address 172.18.20.5 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# ! GigabitEthernet interface 1/0/0 is in area 2: 
      Device(config)# interface GigabitEthernet 1/0/0 
      Device(config-if)# ip address 172.18.1.5 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# ! GigabitEthernet interface 2/0/0 is in area 2: 
      Device(config)# interface GigabitEthernet 2/0/0 
      Device(config-if)# ip address 172.18.2.5 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# ! GigabitEthernet interface 3/0/0 is in area 3:
      Device(config)# interface GigabitEthernet 3/0/0 
      Device(config-if)# ip address 172.19.10.5 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# ! GigabitEthernet interface 4/0/0 is in area 0:
      Device(config)# interface GigabitEthernet 4/0/0 
      Device(config-if)# ip address 172.19.1.1 255.255.255.0
      Device(config-if)# exit 
      Device(config)# ! GigabitEthernet interface 5/0/0 is in area 0:
      Device(config)# interface GigabitEthernet 5/0/0 
      Device(config-if)# ip address 10.1.0.1 255.255.0.0 
      Device(config-if)# !
      

      Each network router configuration command is evaluated sequentially, so the specific order of these commands in the configuration is important. The Cisco software sequentially evaluates the address/wildcard-mask pair for each interface. See the IP Routing Protocols 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 Gigabit Ethernet interface 0/0/0. Gigabit Ethernet interface 0/0/0 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 Gigabit Ethernet interface 0/0/0). Assume that a match is determined for Gigabit Ethernet interface 1/0/0. OSPF is then enabled for that interface, and Gigabit Ethernet 1/0/0 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 Device ABR and ASBRs Configuration

      The figure below provides a general network map that illustrates a sample configuration for several devices within a single OSPF autonomous system.

      Figure 2. Example OSPF Autonomous System Network Map

      In this configuration, five devices are configured in OSPF autonomous system 1:

      • Device A and Device B are both internal devices within area 1.
      • Device C is an OSPF ABR. Note that for Device C, area 1 is assigned to E3 and Area 0 is assigned to S0.
      • Device D is an internal device in area 0 (backbone area). In this case, both network router configuration commands specify the same area (area 0, or the backbone area).
      • Device E is an OSPF ASBR. Note that the Border Gateway Protocol (BGP) routes are redistributed into OSPF and that these routes are advertised by OSPF.

      Note


      Definitions of all areas in an OSPF autonomous system need not be included in the configuration of all devices 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 devices in area 1 (Device A and Device B) when the ABR (Device C) injects summary link state advertisements (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 sample configuration for the general network map shown in the figure above.

      Device A Configuration--Internal Device
      Device(config)# interface GigabitEthernet 1/0/0 
      Device(config-if)# ip address 192.168.1.1 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# router ospf 1 
      Device(config-router)# network 192.168.1.0 0.0.0.255 area 1 
      Device(config-router)# exit 
      
      Device B Configuration--Internal Device
      Device(config)# interface GigabitEthernet 2/0/0 
      Device(config-if)# ip address 192.168.1.2 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# router ospf 1 
      Device(config-router)# network 192.168.1.0 0.0.0.255 area 1 
      Device(config-router)# exit 
      
      Device C Configuration--ABR
      Device(config)# interface GigabitEthernet 3/0/0 
      Device(config-if)# ip address 192.168.1.3 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# interface Serial 0/0/0 
      Device(config-if)# ip address 192.168.2.3 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# router ospf 1 
      Device(config-router)# network 192.168.1.0 0.0.0.255 area 1 
      Device(config-router)# network 192.168.2.0 0.0.0.255 area 0 
      Device(config-router)# exit 
      
      Device D Configuration--Internal Device
      Device(config)# interface GigabitEthernet 4/0/0
      Device(config-if)# ip address 10.0.0.4 255.0.0.0 
      Device(config-if)# exit 
      Device(config)# interface Serial 1/0/0 
      Device(config-if)# ip address 192.168.2.4 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# router ospf 1 
      Device(config-router)# network 192.168.2.0 0.0.0.255 area 0 
      Device(config-router)# network 10.0.0.0 0.255.255.255 area 0 
      Device(config-router)# exit 
      
      Device E Configuration--ASBR
      Device(config)# interface GigabitEthernet 5/0/0 
      Device(config-if)# ip address 10.0.0.5 255.0.0.0 
      Device(config-if)# exit 
      Device(config)# interface Serial 2/0/0 
      Device(config-if)# ip address 172.16.1.5 255.255.255.0 
      Device(config-if)# exit 
      Device(config)# router ospf 1 
      Device(config-router)# network 10.0.0.0 0.255.255.255 area 0 
      Device(config-router)# redistribute bgp 50000 metric 1 metric-type 1 
      Device(config-router)# exit 
      Device(config)# router bgp 50000 
      Device(config-router)# network 192.168.0.0 
      Device(config-router)# network 10.0.0.0 
      Device(config-router)# neighbor 172.16.1.6 remote-as 60000
      

      Example: Complex OSPF Configuration

      The following sample 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. The figure below 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 Gigabit Ethernet interface 0/0/0 through Gigabit Ethernet interface 3/0/0.
      • 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 the Enhanced Interior Gateway Routing Protocol (EIGRP) and the Routing Information Protocol (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:

      Device(config)# interface GigabitEthernet 0/0/0
      Device(config-if)# ip address 192.168.110.201 255.255.255.0 
      Device(config-if)# ip ospf authentication-key abcdefgh 
      Device(config-if)# ip ospf cost 10 
      Device(config-if)# exit 
      Device(config)# interface GigabitEthernet 1/0/0 
      Device(config-if)# ip address 172.19.251.201 255.255.255.0 
      Device(config-if)# ip ospf authentication-key ijklmnop 
      Device(config-if)# ip ospf cost 20 
      Device(config-if)# ip ospf retransmit-interval 10 
      Device(config-if)# ip ospf transmit-delay 2 
      Device(config-if)# ip ospf priority 4 
      Device(config-if)# exit 
      Device(config)# interface GigabitEthernet 2/0/0
      Device(config-if)# ip address 172.19.254.201 255.255.255.0 
      Device(config-if)# ip ospf authentication-key abcdefgh 
      Device(config-if)# ip ospf cost 10 
      Device(config-if)# exit 
      Device(config)# interface GigabitEthernet 3/0/0
      Device(config-if)# ip address 10.56.0.201 255.255.0.0 
      Device(config-if)# ip ospf authentication-key ijklmnop 
      Device(config-if)# ip ospf cost 20 
      Device(config-if)# ip ospf dead-interval 80 
      Device(config-if)# exit 
      

      In the following configuration, OSPF is on network 172.19.0.0:

      Device(config)# router ospf 1 
      Device(config-router)# network 10.0.0.0 0.255.255.255 area 10.0.0.0 
      Device(config-router)# network 192.168.110.0 0.0.0.255 area 192.168.110.0 
      Device(config-router)# network 172.19.0.0 0.0.255.255 area 0 
      Device(config-router)# area 0 authentication 
      Device(config-router)# area 10.0.0.0 stub 
      Device(config-router)# area 10.0.0.0 authentication 
      Device(config-router)# area 10.0.0.0 default-cost 20 
      Device(config-router)# area 192.168.110.0 authentication 
      Device(config-router)# area 10.0.0.0 range 10.0.0.0 255.0.0.0 
      Device(config-router)# area 192.168.110.0 range 192.168.110.0 255.255.255.0 
      Device(config-router)# area 0 range 172.19.251.0 255.255.255.0 
      Device(config-router)# area 0 range 172.19.254.0 255.255.255.0 
      Device(config-router)# redistribute eigrp 200 metric-type 2 metric 1 tag 200 subnets 
      Device(config-router)# redistribute rip metric-type 2 metric 1 tag 200 
      Device(config-router)# exit 
      

      In the following configuration, EIGRP autonomous system 1 is on 172.19.0.0:

      Device(config)# router eigrp 1 
      Device(config-router)# network 172.19.0.0 
      Device(config-router)# exit 
      Device(config)# ! RIP for 192.168.110.0: 
      Device(config)# router rip 
      Device(config-router)# network 192.168.110.0 
      Device(config-router)# redistribute eigrp 1 metric 1 
      Device(config-router)# redistribute ospf 201 metric 1 
      Device(config-router)# exit
      

      Example: Default Metric Values Redistribution

      The following example shows a device in autonomous system 1 that is configured to run both the Routing Information Protocol (RIP) and the Enhanced Interior Gateway Routing Protocol (EIGRP). The example advertises EIGRP-derived routes using RIP and assigns the EIGRP-derived routes a RIP metric of 10.

      Device(config)# router rip 
      Device(config-router)# redistribute eigrp 1 
      Device(config-router)# default-metric 10 
      Device(config-router)# exit 
      

      Examples: Redistribution With and Without Route Maps

      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 Open Shortest Path First (OSPF) routes into the Enhanced Interior Gateway Routing Protocol (EIGRP):

      Device(config)# router eigrp 1 
      Device(config-router)# redistribute ospf 101 
      Device(config-router)# exit 
      

      The following example redistributes Routing Information Protocol (RIP) routes with a hop count equal to 1 into OSPF. These routes will be redistributed into OSPF as external link state advertisements (LSAs) with a metric of 5, metric a type of type 1, and a tag equal to 1.

      Device(config)# router ospf 1 
      Device(config-router)# redistribute rip route-map rip-to-ospf 
      Device(config-router)# exit 
      Device(config)# route-map rip-to-ospf permit 
      Device(config-route-map)# match metric 1 
      Device(config-route-map)# set metric 5 
      Device(config-route-map)# set metric-type type 1 
      Device(config-route-map)# set tag 1 
      Device(config-route-map)# exit 
      

      The following example redistributes OSPF learned routes with tag 7 as a RIP metric of 15:

      Device(config)# router rip 
      Device(config-router)# redistribute ospf 1 route-map 5 
      Device(config-router)# exit 
      Device(config)# route-map 5 permit 
      Device(config-route-map)# match tag 7 
      Device(config-route-map)# set metric 15 
      

      The following example redistributes OSPF intra-area and interarea routes with next hop devices on serial interface 0/0/0 into the Border Gateway Protocol (BGP) with an INTER_AS metric of 5:

      Device(config)# router bgp 50000 
      Device(config-router)# redistribute ospf 1 route-map 10 
      Device(config-router)# exit 
      Device(config)# route-map 10 permit 
      Device(config-route-map)# match route-type internal 
      Device(config-route-map)# match interface serial 0/0/0 
      Device(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.

      Device(config)# router isis 
      Device(config-router)# redistribute ospf 1 route-map 2 
      Device(config-router)# redistribute iso-igrp nsfnet route-map 3 
      Device(config-router)# exit 
      Device(config)# route-map 2 permit 
      Device(config-route-map)# match route-type external 
      Device(config-route-map)# match tag 5 
      Device(config-route-map)# set metric 5 
      Device(config-route-map)# set level level-2 
      Device(config-route-map)# exit 
      Device(config)# route-map 3 permit 
      Device(config-route-map)# match address 2000 
      Device(config-route-map)# set metric 30 
      Device(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.

      Device(config)# router rip 
      Device(config-router)# redistribute ospf 101 route-map 1 
      Device(config-router)# exit 
      Device(config)# route-map 1 permit 
      Device(config-route-map)# match tag 1 2 
      Device(config-route-map)# set metric 1 
      Device(config-route-map)# exit 
      Device(config)# route-map 1 permit 
      Device(config-route-map)# match tag 3 
      Device(config-route-map)# set metric 5 
      Device(config-route-map)# exit 
      Device(config)# route-map 1 deny 
      Device(config-route-map)# match tag 4 
      Device(config-route-map)# exit 
      Device(config)# route map 1 permit 
      Device(config-route-map)# match tag 5 
      Device(config-route-map)# set metric 5 
      Device(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:

      Device(config)# router isis 
      Device(config-router)# redistribute rip route-map 1 
      Device(config-router)# redistribute iso-igrp remote route-map 1 
      Device(config-router)# exit 
      Device(config)# route-map 1 permit 
      Device(config-route-map)# match ip address 1 
      Device(config-route-map)# match clns address 2 
      Device(config-route-map)# set metric 5 
      Device(config-route-map)# set level level-2 
      Device(config-route-map)# exit 
      Device(config)# access-list 1 permit 172.18.0.0 0.0.255.255 
      Device(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.

      Device(config)# route-map ospf-default permit 
      Device(config-route-map)# match ip address 1 
      Device(config-route-map)# set metric 5 
      Device(config-route-map)# set metric-type type-2 
      Device(config-route-map)# exit 
      Device(config)# access-list 1 172.20.0.0 0.0.255.255 
      Device(config)# router ospf 101 
      Device(config-router)# default-information originate route-map ospf-default 
      

      Examples: Key Management

      The following example configures a key chain named chain1. In this example, the software always accepts and sends key1 as a valid key. The key key2 is accepted from 1:30 p.m. to 3:30 p.m. and is 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 device. Likewise, the key key3 immediately follows key2, and there is 30-minutes on each side to handle time-of-day differences.

      Device(config)# interface GigabitEthernet 0/0/0
      Device(config-if)# ip rip authentication key-chain chain1 
      Device(config-if)# ip rip authentication mode md5 
      Device(config-if)# exit 
      Device(config)# router rip
      Device(config-router)# network 172.19.0.0 
      Device(config-router)# version 2 
      Device(config-router)# exit 
      Device(config)# key chain chain1 
      Device(config-keychain)# key 1 
      Device(config-keychain-key)# key-string key1 
      Device(config-keychain-key)# exit
      Device(config-keychain)# key 2 
      Device(config-keychain-key)# key-string key2 
      Device(config-keychain-key)# accept-lifetime 13:30:00 Jan 25 2005 duration 7200 
      Device(config-keychain-key)# send-lifetime 14:00:00 Jan 25 2005 duration 3600 
      Device(config-keychain-key)# exit
      Device(config-keychain)# key 3 
      Device(config-keychain-key)# key-string key3 
      Device(config-keychain-key)# accept-lifetime 14:30:00 Jan 25 2005 duration 7200 
      Device(config-keychain-key)# send-lifetime 15:00:00 Jan 25 2005 duration 3600 
      Device(config-keychain-key)# end 
      

      The following example configures a key chain named chain1:

      Device(config)# key chain chain1 
      Device(config-keychain)# key 1 
      Device(config-keychain-key)# key-string key1 
      Device(config-keychain-key)# exit
      Device(config-keychain)# key 2 
      Device(config-keychain-key)# key-string key2 
      Device(config-keychain-key)# accept-lifetime 00:00:00 Dec 5 2004 23:59:59 Dec 5 2005 
      Device(config-keychain-key)# send-lifetime 06:00:00 Dec 5 2004 18:00:00 Dec 5 2005 
      Device(config-keychain-key)# exit 
      Device(config-keychain)# exit 
      Device(config)# interface GigabitEthernet 0/0/0 
      Device(config-if)# ip address 172.19.104.75 255.255.255.0 secondary 172.19.232.147 255.255.255.240 
      Device(config-if)# ip rip authentication key-chain chain1 
      Device(config-if)# media-type 10BaseT 
      Device(config-if)# exit 
      Device(config)# interface GigabitEthernet 1/0/0
      Device(config-if)# no ip address 
      Device(config-if)# shutdown 
      Device(config-if)# media-type 10BaseT 
      Device(config-if)# exit 
      Device(config)# interface Fddi 0 
      Device(config-if)# ip address 10.1.1.1 255.255.255.0 
      Device(config-if)# no keepalive 
      Device(config-if)# exit 
      Device(config)# interface Fddi 1/0/0
      Device(config-if)# ip address 172.16.1.1 255.255.255.0 
      Device(config-if)# ip rip send version 1 
      Device(config-if)# ip rip receive version 1 
      Device(config-if)# no keepalive 
      Device(config-if)# exit 
      Device(config)# router rip 
      Device(config-router)# version 2 
      Device(config-router)# network 172.19.0.0 
      Device(config-router)# network 10.0.0.0 
      Device(config-router)# network 172.16.0.0 
      

      Additional References

      Related Documents

      Related Topic

      Document Title

      Cisco IOS master command list, all releases

      Cisco IOS Master Command List, All Releases

      IP routing protocol-independent commands: complete command syntax, command mode, defaults, usage guidelines, and examples

      Cisco IOS IP Routing: Protocol-Independent Command Reference

      Performing basic system management

      Basic System Management Configuration Guide

      Changing the maximum number of paths

      "BGP Multipath Load Sharing for Both eBGP and iBGP in an MPLS-VPN" module in the BGP Configuration Guide

      BGP route map configuration tasks and configuration examples.

      "Connecting to a Service Provider Using External BGP" module in the BGP Configuration Guide

      BGP communities and route maps.

      "BGP Cost Community" module in the BGP Configuration Guide

      RFCs

      RFC

      Title

      RFC 791

      Internet Protocol

      RFC 1219

      Variable-Length Subnet Masks

      Technical Assistance

      Description

      Link

      The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

      To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

      Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

      http:/​/​www.cisco.com/​techsupport

      Feature Information for Basic IP Routing

      The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

      Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

      Table 2 Feature Information for Basic IP Routing

      Feature Name

      Releases

      Feature Information

      IP Routing

      The IP Routing feature introduced basic IP routing features that are documented throughout this module and also in other IP Routing Protocol modules.