IP Routing: Protocol-Independent Configuration Guide, Cisco IOS XE Release 3S
PBR Recursive Next Hop
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PBR Recursive Next Hop

The PBR Recursive Next Hop feature enhances route maps to enable configuration of a recursive next-hop IP address that is used by policy-based routing (PBR). The recursive next-hop IP address is installed in the routing table and can be a subnet that is not directly connected. If the recursive next-hop IP address is not available, packets are routed using a default route.

Because Cisco Express Forwarding (CEF) or process switching provides the infrastructure, the benefit of this feature is the CEF loadsharing.

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.

Restrictions for PBR Recursive Next Hop

If there are multiple equal-cost routes to the subnet that have been configured by the set next-hop recursive command, load balancing will occur only if all the adjacencies to the routes are resolved. If any of the adjacencies have not been resolved, load balancing will not occur and only one of the routes whose adjacency is resolved will be used. If none of the adjacencies are resolved, then the packets will be processed, resulting in the resolution of at least one of the adjacencies, leading to the programming of the adjacency in the hardware. Policy based routing relies on routing protocols or other means to resolve all adjacencies and as a result, load balancing occurs.

How to Configure PBR Recursive Next Hop

Setting the Recursive Next-Hop IP Address

The infrastructure provided by CEF or process switching performs the recursion to the next-hop IP address. The configuration sequence, which affects routing, is as follows:

  1. Next-hop
  2. Next-hop recursive
  3. Interface
  4. Default next-hop
  5. Default interface

If both a next-hop address and a recursive next-hop IP address are present in the same route-map entry, the next hop is used. If the next hop is not available, the recursive next hop is used. If the recursive next hop is not available and no other IP address is present, the packet is routed using the default routing table; it is not dropped. If the packet is supposed to be dropped, use the set ip next-hopcommand with the recursive keyword, followed by a set interface null0 configuration.

Perform this task to set the IP address for the recursive next-hop router.

Before You Begin

If loadsharing is required, CEF loadsharing should be configured for per-packet or per-destination loadsharing. Loadbalancing should be done over all equal-cost routes to the subnet that has been configured by the set ip next-hop recursivecommand.

This functionality should be available in centralized and distributed systems.


Note

Only one recursive next-hop IP address is supported per route-map entry.

>
SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    access-list access-list-number {deny | permit} source[source-wildcard] [log]

    4.    route-map map-tag

    5.    set ip next-hop ip-address

    6.    set ip next-hop {ip-address [...ip-address] | recursive ip-address}

    7.    match ip address access-list-number

    8.    end


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Router> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2 configure terminal


    Example:
    Router# configure terminal
     

    Enters global configuration mode.

     
    Step 3 access-list access-list-number {deny | permit} source[source-wildcard] [log]


    Example:
    Router(config)# access-list 101 permit 10.60.0.0 0.0.255.255
     

    Configures an access list. The example configuration permits any source IP address that falls within the 10.60.0.0. 0.0.255.255 subnet.

     
    Step 4 route-map map-tag


    Example:
    Router(config)# route-map abccomp
     

    Enables policy routing and enters route-map configuration mode.

     
    Step 5 set ip next-hop ip-address


    Example:
    Router(config-route-map)# set ip next-hop 10.10.1.1
     

    Sets a next-hop router IP address.

    Note   

    Set this IP address separately from the next-hop recursive router configuration.

     
    Step 6 set ip next-hop {ip-address [...ip-address] | recursive ip-address}


    Example:
    Router(config-route-map)# set ip next-hop recursive 10.20.3.3
     

    Sets a recursive next-hop IP address.

    Note   

    This configuration does not ensure that packets get routed using the recursive IP address if an intermediate IP address is a shorter route to the destination.

     
    Step 7 match ip address access-list-number


    Example:
    Router(config-route-map)# match ip address 101
     

    Sets an access list to be matched.

     
    Step 8 end


    Example:
    Router(config-route-map)# end
     

    Exits route-map configuration mode and returns to privileged EXEC mode.

     

    Verifying the Recursive Next-Hop Configuration

    To verify the recursive next-hop configuration, perform the following steps.

    SUMMARY STEPS

      1.    show running-config | begin abccomp

      2.    show route-map map-name


    DETAILED STEPS
      Step 1   show running-config | begin abccomp

      Use this command to verify the IP addresses for a next-hop and recursive next-hop IP address, for example:



      Example:
      Router# show running-config | begin abccomp
route-map abccomp permit 10
 match ip address 101 ! Defines the match criteria for an access list.
 set ip next-hop recursive 10.3.3.3 ! If the match criteria are met, the recursive IP  address is set.
 set ip next-hop 10.1.1.1 10.2.2.2 10.4.4.4
      Step 2   show route-map map-name

      Use this command to display the route maps, for example:



      Example:
      Router# show route-map abccomp
route-map abccomp, permit, sequence 10
 Match clauses:
  ip address (access-lists): 101 
 Set clauses:
  ip next-hop recursive 10.3.3.3
  ip next-hop 10.1.1.1 10.2.2.2 10.4.4.4
 Policy routing matches: 0 packets, 0 bytes

      Configuration Examples for PBR Recursive Next Hop

      Recursive Next-Hop IP Address Example

      The following example shows the configuration of IP address 10.3.3.3 as the recursive next-hop router:

      route-map abccomp
 set ip next-hop 10.1.1.1
 set ip next-hop 10.2.2.2
 set ip next-hop recursive 10.3.3.3
 set ip next-hop 10.4.4.4

      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 PBR Recursive Next Hop

      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 1 Feature Information for PBR Recursive Next Hop

      Feature Name

      Releases

      Feature Information

      PBR Recursive Next Hop

      Cisco IOS XE Release 2.2

      This feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

      The following commands were modified by this feature: set ip next-hop, show route-map.