Cisco IOS XR IP Addresses and Services Configuration Guide for the Cisco XR 12000 Series Router, Release 4.3.x
Implementing Cisco Express Forwarding
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Implementing Cisco Express Forwarding

Contents

Implementing Cisco Express Forwarding

Cisco Express Forwarding (CEF) is advanced, Layer 3 IP switching technology. CEF optimizes network performance and scalability for networks with large and dynamic traffic patterns, such as the Internet, on networks characterized by intensive web-based applications, or interactive sessions.


Note


For complete descriptions of the CEF commands listed in this module, you can refer to the Related Documents section of this module. To locate documentation for other commands that might appear in the course of executing a configuration task, search online in the master command index.


Feature History for Implementing CEF

Release

Modification

Release 3.2

This feature was introduced.

Release 3.3.0

Loose and Strict support for uRPF was added.

The CEF Nonrecursive Accounting feature was removed.

Release 3.5.0

IPv4 Strict uRPF support was added.

Release 3.7.0

The show cef bgp-attribute command was added.

Release 4.1.0

The N-Tuple Hashing feature was added.

Prerequisites for Implementing Cisco Express Forwarding

The following prerequisites are required to implement Cisco Express Forwarding:

  • You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Information About Implementing Cisco Express Forwarding Software

To implement Cisco Express Forwarding features in this document you must understand the following concepts:

Key Features Supported in the Cisco Express Forwarding Implementation

The following features are supported for CEF on Cisco IOS XR software:

  • Border Gateway Protocol (BGP) policy accounting
  • Reverse path forwarding (RPF)
  • Virtual interface support
  • Multipath support
  • Route consistency
  • High availability features such as packaging, restartability, and Out of Resource (OOR) handling
  • OSPFv2 SPF prefix prioritization
  • BGP attributes download

Benefits of CEF

CEF offers the following benefits:

  • Improved performance—CEF is less CPU-intensive than fast-switching route caching. More CPU processing power can be dedicated to Layer 3 services such as quality of service (QoS) and encryption.
  • Scalability—CEF offers full switching capacity at each line card.
  • Resilience—CEF offers an unprecedented level of switching consistency and stability in large dynamic networks. In dynamic networks, fast-switched cache entries are frequently invalidated due to routing changes. These changes can cause traffic to be process switched using the routing table, rather than fast switched using the route cache. Because the Forwarding Information Base (FIB) lookup table contains all known routes that exist in the routing table, it eliminates route cache maintenance and the fast-switch or process-switch forwarding scenario. CEF can switch traffic more efficiently than typical demand caching schemes.

CEF Components

Cisco IOS XR softwareCEF always operates in CEF mode with two distinct components: a Forwarding Information Base (FIB) database and adjacency table—a protocol-independent adjacency information base (AIB).

CEF is a primary IP packet-forwarding database for Cisco IOS XR software. CEF is responsible for the following functions:

  • Software switching path
  • Maintaining forwarding table and adjacency tables (which are maintained by the AIB) for software and hardware forwarding engines

The following CEF forwarding tables are maintained in Cisco IOS XR software:

  • IPv4 CEF database
  • IPv6 CEF database
  • MPLS LFD database
  • Multicast Forwarding Table (MFD)

The protocol-dependent FIB process maintains the forwarding tables for IPv4 and IPv6 unicast in the route processor ( RP) and each MSC.

The FIB on each node processes Routing Information Base (RIB) updates, performing route resolution and maintaining FIB tables independently in the RP and each MSC. FIB tables on each node can be slightly different. Adjacency FIB entries are maintained only on a local node, and adjacency entries linked to FIB entries could be different.

Border Gateway Protocol Policy Accounting

Border Gateway Protocol (BGP) policy accounting measures and classifies IP traffic that is sent to, or received from, different peers. Policy accounting is enabled on an individual input or output interface basis, and counters based on parameters such as community list, autonomous system number, or autonomous system path are assigned to identify the IP traffic.


Note


There are two types of route policies. The first type (regular BGP route policies) is used to filter the BGP routes advertised into or out from the BGP links. This type of route policy is applied to the specific BGP neighbor. The second type (specific route policy) is used to set up a traffic index for the BGP prefixes. This route policy is applied to the global BGP IPv4 address family to set up the traffic index when the BGP routes are inserted into the RIB table. BGP policy accounting uses the second type of route policy.


Using BGP policy accounting, you can account for traffic according to the route it traverses. Service providers can identify and account for all traffic by customer and bill accordingly. In Figure 1, BGP policy accounting can be implemented in Router A to measure packet and byte volumes in autonomous system buckets. Customers are billed appropriately for traffic that is routed from a domestic, international, or satellite source.


Note


BGP policy accounting measures and classifies IP traffic for BGP prefixes only.


Figure 1. Sample Topology for BGP Policy Accounting

Based on the specified routing policy, BGP policy accounting assigns each prefix a traffic index (bucket) associated with an interface. BGP prefixes are downloaded from the Routing Information Base (RIB) to the FIB along with the traffic index.

There are a total of 63 (1 to 63) traffic indexes (bucket numbers) that can be assigned for BGP prefixes. Internally, there is an accounting table associated with the traffic indexes to be created for each input (ingress) and output (egress) interface. The traffic indexes allow you to account for the IP traffic, where the source IP address, the destination IP address, or both are BGP prefixes.


Note


Traffic index 0 contains the packet count using Interior Gateway Protocol (IGP) routes.


Reverse Path Forwarding (Strict and Loose)

Unicast IPv4 and IPv6 Reverse Path Forwarding (uRPF), both strict and loose modes, help mitigate problems caused by the introduction of malformed or spoofed IP source addresses into a network by discarding IP packets that lack a verifiable IP source address. Unicast RPF does this by doing a reverse lookup in the CEF table. Therefore, Unicast Reverse Path Forwarding is possible only if CEF is enabled on the router.

Cisco IOS XR softwaresupports both modes of Unicast IPv4 Reverse Path Forwarding on all IP Services Engine (ISE/Engine 3) and Engine 5 line cards in the and the strict mode of Unicast IPv6 Reverse Path Forwarding on Engine 5 line cards.


Note


Unicast RPF allows packets with 0.0.0.0 source addresses and 255.255.255.255 destination addresses to pass so that Bootstrap Protocol and Dynamic Host Configuration Protocol (DHCP) will function properly.


When strict uRPF is enabled, the source address of the packet is checked in the FIB. If the packet is received on the same interface that would be used to forward the traffic to the source of the packet, the packet passes the check and is further processed; otherwise, it is dropped. Strict uRPF should only be applied where there is natural or configured symmetry. Because internal interfaces are likely to have routing asymmetry, that is, multiple routes to the source of a packet, strict uRPF should not be implemented on interfaces that are internal to the network.


Note


The behavior of strict RPF varies slightly by platform, number of recursion levels, and number of paths in Equal-Cost Multipath (ECMP) scenarios. A platform may switch to loose RPF check for some or all prefixes, even though strict RPF is configured.


When loose uRPF is enabled, the source address of the packet is checked in the FIB. If it exists and matches a valid forwarding entry, the packet passes the check and is further processed; otherwise, it is dropped.

Loose and strict uRPF supports two options: allow self-ping and allow default. The self-ping option allows the source of the packet to ping itself. The allow default option allows the lookup result to match a default routing entry. When the allow default option is enabled with the strict mode of the uRPF, the packet is processed further only if it arrived through the default interface.


Note


On s, strict uRPF supports load-balanced prefixes for a maximum of eight interfaces on the same line card. When a packet is received on a load-balanced prefix, it is verified against each of the interfaces in the load balance. If a packet is received on a load-balanced prefix with more than eight interfaces on the same line card, a loose uRPF check is performed, even if the packet is received on an interface that was configured for strict uRPF.


Per-Flow Load Balancing

Load balancing describes the functionality in a router that distributes packets across multiple links based on Layer 3 (network layer) and Layer 4 (transport layer) routing information. If the router discovers multiple paths to a destination, the routing table is updated with multiple entries for that destination.

Per-flow load balancing performs these functions:

  • Incoming data traffic is evenly distributed over multiple equal-cost connections.
  • Incoming data Data traffic is evenly distributed over multiple equal-cost connections member links within a bundle interface.
  • Layer 2 bundle and Layer 3 (network layer) load balancing decisions are taken on IPv4, IPv6, which are supported for the 7-tuple hash algorithm.
  • A 7-tuple hash algorithm provides more granular load balancing than the existing 3-tuple hash algorithm.
  • The same hash algorithm (3-tuple or 7-tuple) is used for load balancing over multiple equal-cost Layer 3 (network layer) paths. The Layer 3 (network layer) path is on a physical interface or on a bundle interface. In addition, load balancing over member links can occur within a Layer 2 bundle interface.
  • The cef load-balancing fields command allows you to select either the 3-tuple hash algorithm (default) or the 7-tuple hash algorithm.

The 3-tuple load-balance hash calculation contains these Layer 3 (Network Layer) inputs:

Layer 3 (Network Layer) Routing Information

  • Source IP address
  • Destination IP address
  • Router ID

The 7-tuple load-balance hash calculation contains 3-tuple inputs and these additional following Layer 4 (Transport Layer) inputs:

Layer 4 (Transport Layer) Routing Information

  • Source port
  • Destination port
  • Protocol
  • Router ID
  • Slot Number:Rx UIDB Index

Note


In load-balancing scenarios, a line card may not use all output paths downloaded from routing protocols. This behavior varies with platform, number of recursion levels, and the fact whether MPLS is involved, or not.


BGP Attributes Download

The BGP Attributes Download feature enables you to display the installed BGP attributes in CEF. Configure the show cef bgp-attribute command to display the installed BGP attributes in CEF. You can use the show cef bgp-attribute attribute-id command and the show cef bgp-attribute local-attribute-id command to look at specific BGP attributes by attribute ID and local attribute ID.

How to Implement CEF

This section contains instructions for the following tasks:

Verifying CEF

This task allows you to verify CEF.

SUMMARY STEPS

    1.    show cef {ipv4 | ipv6}

    2.    show cef {ipv4 | ipv6} summary

    3.    show cef {ipv4 | ipv6} detail

    4.    show adjacency detail


DETAILED STEPS
     Command or ActionPurpose
    Step 1 show cef {ipv4 | ipv6}


    Example:
    RP/0/0/CPU0:router# show cef ipv4
    
     

    Displays the IPv4 or IPv6 CEF table. The next hop and forwarding interface are displayed for each prefix.

    Note   

    The output of the show cef command varies by location.

     
    Step 2 show cef {ipv4 | ipv6} summary


    Example:
    RP/0/0/CPU0:router# show cef ipv4 summary
    
     

    Displays a summary of the IPv4 or IPv6 CEF table.

     
    Step 3 show cef {ipv4 | ipv6} detail


    Example:
    RP/0/0/CPU0:router# show cef ipv4 detail
    
     

    Displays detailed IPv4 or IPv6 CEF table information.

     
    Step 4 show adjacency detail


    Example:
    RP/0/0/CPU0:router# show adjacency detail
    
     

    Displays detailed adjacency information, including Layer 2 information for each interface.

    Note   

    The output of the show adjacency command varies by location.

     

    Configuring BGP Policy Accounting

    This task allows you to configure BGP policy accounting.


    Note


    There are two types of route policies. BGP policy accounting uses the type that is used to set up a traffic index for the BGP prefixes. The route policy is applied to the global BGP IPv4 address family to set up the traffic index when the BGP routes are inserted into the RIB table.


    BGP policy accounting enables per interface accounting for ingress and egress IP traffic based on the traffic index assigned to the source IP address (BGP prefix) and destination IP address (BGP prefix). The traffic index of BGP prefixes can be assigned according to the following parameters using Routing Policy Language (RPL):

    • prefix-set
    • AS-path-set
    • community-set

    Note


    BGP policy accounting is supported on IPv4 prefixes only.


    Two configuration tasks provide the ability to classify BGP prefixes that are in the RIB according to the prefix-set, AS-path-set, or the community-set parameters:

    1. Use the route-policy command to define the policy for traffic index setup based on the prefix-set, AS-path-set, or community-set.
    2. Use the BGP table-policy command to apply the defined route policy to the global BGP IPv4 unicast address family.

    See the Cisco IOS XR Routing Command Reference for the Cisco XR 12000 Series Router for information on the route-policy and table-policy commands.

    BGP policy accounting can be enabled on each interface with the following options:

    • Use the ipv4 bgp policy accounting command with one of the following keyword options:
      • input source-accounting
      • input destination-accounting
      • input source-accounting destination-accounting
    • Use the ipv4 bgp policy accounting command with one of the following keyword options:
      • output source-accounting
      • output destination-accounting
      • output source-accounting destination-accounting
    • Use any combination of the keywords provided for the ipv4 bgp policy accounting command.
    Before You Begin

    Before using the BGP policy accounting feature, you must enable BGP on the router (CEF is enabled by default). See the Cisco IOS XR Routing Configuration Guide for the Cisco XR 12000 Series Router for information on enabling BGP.

    Verifying BGP Policy Accounting

    This task allows you to verify BGP policy accounting.


    Note


    BGP policy accounting is supported on IPv4 prefixes.


    Before You Begin

    BGP policy accounting must be configured. See the Configuring BGP Policy Accounting.

    SUMMARY STEPS

      1.    show route bgp

      2.    show bgp summary

      3.    show bgp ip-address

      4.    show route ipv4 ip-address

      5.    show cef ipv4 prefix

      6.    show cef ipv4 prefix detail

      7.    show cef ipv4 interface type interface-path-id bgp-policy-statistics


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 show route bgp


      Example:
      RP/0/0/CPU0:router# show route bgp
      
       

      Displays all BGP routes with traffic indexes.

       
      Step 2 show bgp summary


      Example:
      RP/0/0/CPU0:router# show bgp summary
      
       

      Displays the status of all BGP neighbors.

       
      Step 3 show bgp ip-address


      Example:
      RP/0/0/CPU0:router# show bgp 40.1.1.1
      
       

      Displays BGP prefixes with BGP attributes.

       
      Step 4 show route ipv4 ip-address


      Example:
      RP/0/0/CPU0:router# show route ipv4 40.1.1.1
      
       

      Displays the specific BGP route with the traffic index in the RIB.

       
      Step 5 show cef ipv4 prefix


      Example:
      RP/0/0/CPU0:router# show cef ipv4 40.1.1.1
      
       

      Displays the specific BGP prefix with the traffic index in the RP FIB.

       
      Step 6 show cef ipv4 prefix detail


      Example:
      RP/0/0/CPU0:router# show cef ipv4 40.1.1.1 detail
      
       

      Displays the specific BGP prefix with detailed information in the RP FIB.

       
      Step 7 show cef ipv4 interface type interface-path-id bgp-policy-statistics


      Example:
      RP/0/0/CPU0:router# show cef ipv4 interface TenGigE 0/2/0/4 bgp-policy-statistics
      
       

      Displays the BGP Policy Accounting statistics for the specific interface.

       

      Configuring a Route Purge Delay

      This task allows you to configure a route purge delay. A purge delay purges routes when the RIB or other related process experiences a failure.

      SUMMARY STEPS

        1.    configure

        2.    cef purge-delay seconds

        3.    Use the commit or end command.


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 configure


        Example:
        RP/0/0/CPU0:router# configure
         

        Enters global configuration mode.

         
        Step 2 cef purge-delay seconds


        Example:
        RP/0/0/CPU0:router(config)# cef purge-delay 180
        
         

        Configures a delay in purging routes when the Routing Information Base (RIB) or other related processes experience a failure.

         
        Step 3 Use the commit or end command.  

        commit—Saves the configuration changes and remains within the configuration session.

        end—Prompts user to take one of these actions:
        • Yes— Saves configuration changes and exits the configuration session.
        • No—Exits the configuration session without committing the configuration changes.
        • Cancel—Remains in the configuration mode, without committing the configuration changes.
         

        Configuring Unicast RPF Checking

        This task allows you to configure unicast Reverse Path Forwarding (uRPF) RPF checking. Unicast RPF checking allows you to mitigate problems caused by malformed or forged (spoofed) IP source addresses that pass through a router. Malformed or forged source addresses can indicate denial-of-service (DoS) attacks based on source IP address spoofing.

        SUMMARY STEPS

          1.    configure

          2.    interface type interface-path-id

          3.    {ipv4 | ipv6} verify unicast source reachable-via {any | rx} [allow-default] [allow-self-ping]

          4.    Use the commit or end command.


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 configure


          Example:
          RP/0/0/CPU0:router# configure
           

          Enters global configuration mode.

           
          Step 2 interface type interface-path-id


          Example:
          RP/0/0/CPU0:router(config)# interface GigabitEthernet 0/1/0/0 
          
           

          Enters interface configuration mode.

           
          Step 3 {ipv4 | ipv6} verify unicast source reachable-via {any | rx} [allow-default] [allow-self-ping]


          Example:
          RP/0/0/CPU0:router(config-if)# ipv4 verify unicast source reachable-via rx
          
           

          Enables IPv4 or IPv6 uRPF checking.

          • The rx keyword enables strict unicast RPF checking. If strict unicast RPF is enabled, a packet is not forwarded unless its source prefix exists in the routing table and the output interface matches the interface on which the packet was received.
          • The allow-default keyword enables the matching of default routes. This option applies to both loose and strict RPF.
          • The allow-self-ping keyword enables the router to ping out an interface. This option applies to both loose and strict RPF.
          Note   

          IPv6 uRPF checking is not supported on ASR 9000 Ethernet linecards.

           
          Step 4 Use the commit or end command.  

          commit—Saves the configuration changes and remains within the configuration session.

          end—Prompts user to take one of these actions:
          • Yes— Saves configuration changes and exits the configuration session.
          • No—Exits the configuration session without committing the configuration changes.
          • Cancel—Remains in the configuration mode, without committing the configuration changes.
           

          Configuring Modular Services Card-to-Route Processor Management Ethernet Interface Switching

          This task allows you to enable MSC-to-RP management Ethernet interface switching.

          SUMMARY STEPS

            1.    configure

            2.    rp mgmtethernet forwarding

            3.    Use the commit or end command.


          DETAILED STEPS
             Command or ActionPurpose
            Step 1 configure


            Example:
            RP/0/0/CPU0:router# configure
             

            Enters global configuration mode.

             
            Step 2 rp mgmtethernet forwarding


            Example:
            RP/0/0/CPU0:router(config)# rp mgmtethernet forwarding
            
             

            Enables switching from the MSC to the route processor Management Ethernet interfaces.

             
            Step 3 Use the commit or end command.  

            commit—Saves the configuration changes and remains within the configuration session.

            end—Prompts user to take one of these actions:
            • Yes— Saves configuration changes and exits the configuration session.
            • No—Exits the configuration session without committing the configuration changes.
            • Cancel—Remains in the configuration mode, without committing the configuration changes.
             

            Configuring Per-Flow Load Balancing

            This section describes the following tasks to configure per-flow load balancing:

            Configuring a 7-Tuple Hash Algorithm

            This task allows you to configure per-flow load balancing for a 7-tuple hash algorithm.

            SUMMARY STEPS

              1.    configure

              2.    cef load-balancing fields {L3 | L4}

              3.    Use the commit or end command.

              4.    show cef {ipv4 | ipv6} summary [location node-id]


            DETAILED STEPS
               Command or ActionPurpose
              Step 1 configure


              Example:
              RP/0/0/CPU0:router# configure
               

              Enters global configuration mode.

               
              Step 2 cef load-balancing fields {L3 | L4}


              Example:
              RP/0/0/CPU0:router(config)# cef load-balancing fields L4
              
               

              Configures the hashing algorithm that is used for load balancing during forwarding. The example shows that the L4 field is selected.

              • Use the L3 keyword to specify the Layer 3 load-balancing for the hash algorithm Since L3 is configured as the default value, you do not need to use the cef load-balancing fields command unless you want to configure Layer 4.
              • Use the L4 keyword to specify the Layer 3 and Layer 4 load-balancing for the hash algorithm.

              For a list of the inputs for Layer 3 and Layer 4, see Per-Flow Load Balancing.

               
              Step 3 Use the commit or end command.  

              commit—Saves the configuration changes and remains within the configuration session.

              end—Prompts user to take one of these actions:
              • Yes— Saves configuration changes and exits the configuration session.
              • No—Exits the configuration session without committing the configuration changes.
              • Cancel—Remains in the configuration mode, without committing the configuration changes.
               
              Step 4 show cef {ipv4 | ipv6} summary [location node-id]


              Example:
              RP/0/0/CPU0:router# show cef ipv4 summary
              
               

              Displays the load balancing field for the IPv4 or IPv6 CEF table.

              • (Optional) Use the location keyword display a summary of the IPv4 CEF table for the designated node. The node-id argument is entered in the rack/slot/module notation
               

              Verifying the CEF Exact Route with 7-Tuple Parameters

              The following 7-tuple parameters are specified to obtain the CEF exact route for both IPv4 and IPv6:

              • Source address
              • Destination address
              • Source port and range of destination ports
              • Protocol
              • Ingress interface
              • Router ID

              To display the path an MPLS flow would take, use the show mpls forwarding exact-route command. The MPLS flow comprises a source address and a destination address.

              To display the path a bundle flow would take, use the bundle-hash command. The bundle flow comprises a source and a destination address. For more information, see Cisco IOS XR Interface and Hardware Component Command Reference for the Cisco XR 12000 Series Router .

              To verify the IPv4 7-tuple parameters, perform the following steps:

              SUMMARY STEPS

                1.    Configure parallel interfaces between back-to-back routers.

                2.    Create route traffic streams so that there is a stream placed onto each configured interface.

                3.    Use the show cef ipv4 exact-route command in EXEC mode to verify that the interface selected for load balancing matches with the output from this command. The following example shows the exact route for the Layer 4 information:

                4.    Configure Equal Cost Multipath Protocol (ECMP) interfaces, for example, between back-to-back routers.

                5.    Create route traffic streams so that there is a stream placed onto each configured interface.

                6.    Use the show cef ipv6 exact-route command in EXEC mode to verify that the interface selected for load balancing matches with the output from this command. The following example shows the exact route for the Layer 4 information:


              DETAILED STEPS
                Step 1   Configure parallel interfaces between back-to-back routers.
                Step 2   Create route traffic streams so that there is a stream placed onto each configured interface.
                Step 3   Use the show cef ipv4 exact-route command in EXEC mode to verify that the interface selected for load balancing matches with the output from this command. The following example shows the exact route for the Layer 4 information:

                Example:
                RP/0/0/CPU0:router# show cef ipv4 exact-route 20 .6.1.9 22.6.1.9 protocol udp source-port 1 destination-port 1 ingress-interface GigabitEthernet 0/1/0/4
                
                
                22.6.1.9/32 version 0, internal 0x40040001 (0x78439fd0) [3], 0x0 (0x78aaf928), 0x4400 (0x78ed62d0)  remote adjacency to GigabitEthernet0/1/4/4  Prefix Len 32, traffic index 0, precedence routine (0)
                   via GigabitEthernet0/1/4/4
                

                To verify the IPv6 7-tuple parameters, perform the following steps:

                Step 4   Configure Equal Cost Multipath Protocol (ECMP) interfaces, for example, between back-to-back routers.
                Step 5   Create route traffic streams so that there is a stream placed onto each configured interface.
                Step 6   Use the show cef ipv6 exact-route command in EXEC mode to verify that the interface selected for load balancing matches with the output from this command. The following example shows the exact route for the Layer 4 information:

                Example:
                RP/0/0/CPU0:router# show cef ipv6 exact-route 20:6:1::9 22:6:1::9 protocol udp source-port 1 destination-port 1 ingress-interface GigabitEthernet 0/1/0/4 
                
                
                22:6:1::/64, version 0, internal 0x40000001 (0x7846c048) [3], 0x0 (0x78aea3d0), 0x0 (0x0)  remote adjacency to GigabitEthernet0/1/4/4  Prefix Len 64, traffic index 0, precedence routine (0)
                   via GigabitEthernet0/1/4/4
                

                Configuring BGP Attributes Download

                This task allows you to configure the BGP Attributes Download feature.

                Configuring BGP Attributes Download

                SUMMARY STEPS

                  1.    configure

                  2.    cef bgp attribute {attribute-id | local-attribute-id }

                  3.    Use the commit or end command.


                DETAILED STEPS
                   Command or ActionPurpose
                  Step 1 configure


                  Example:
                  RP/0/0/CPU0:router# configure
                   

                  Enters global configuration mode.

                   
                  Step 2 cef bgp attribute {attribute-id | local-attribute-id }


                  Example:
                  RP/0/0/CPU0:router(config)# cef bgp attribute {attribute-id| local-attribute-id}
                  
                   

                  Configures a CEF BGP attribute.

                   
                  Step 3 Use the commit or end command.  

                  commit—Saves the configuration changes and remains within the configuration session.

                  end—Prompts user to take one of these actions:
                  • Yes— Saves configuration changes and exits the configuration session.
                  • No—Exits the configuration session without committing the configuration changes.
                  • Cancel—Remains in the configuration mode, without committing the configuration changes.
                   

                  Configuration Examples for Implementing CEF on Routers Software

                  This section provides the following configuration examples:

                  Configuring BGP Policy Accounting: Example

                  The following example shows how to configure BGP policy accounting.

                  Configure loopback interfaces for BGP router-id:

                  interface Loopback1
                  ipv4 address 
                  190.1.1.1 255.255.255.255
                  

                  Configure interfaces with the BGP policy accounting options:

                  interface TenGigE0/2/0/2
                   mtu 1514
                   ipv4 address 
                  17.1.0.1 255.255.255.0
                   proxy-arp
                   ipv4 directed-broadcast
                   ipv4 bgp policy accounting input source-accounting destination-accounting
                   ipv4 bgp policy accounting output source-accounting destination-accounting
                  !
                  interface TenGigE0/2/0/2.1
                   ipv4 address 
                  17.1.1.1 255.255.255.0
                   ipv4 bgp policy accounting input source-accounting destination-accounting
                   ipv4 bgp policy accounting output source-accounting destination-accounting
                   encapsulation dot1q 1
                  !
                  interface TenGigE0/2/0/4
                   mtu 1514
                   ipv4 address 
                  18.1.0.1 255.255.255.0
                   proxy-arp
                   ipv4 directed-broadcast
                   ipv4 bgp policy accounting input source-accounting destination-accounting
                   ipv4 bgp policy accounting output source-accounting destination-accounting
                  !
                  interface TenGigE0/2/0/4.1
                   ipv4 address 
                  18.1.
                  1.1 255.255.255.0
                   ipv4 bgp policy accounting input source-accounting destination-accounting
                   ipv4 bgp policy accounting output source-accounting destination-accounting
                   encapsulation dot1q 1
                  !
                  interface GigabitEthernet 0/0/0/4
                   mtu 4474
                   ipv4 address 
                  4.1.0.
                  1 255.255.0.0
                   ipv4 directed-broadcast
                   ipv4 bgp policy accounting input source-accounting destination-accounting
                   ipv4 bgp policy accounting output source-accounting destination-accounting
                   encapsulation ppp
                   GigabitEthernet
                    crc 32
                   !
                   keepalive disable
                  !
                  interface GigabitEthernet 0/0/0/8
                   mtu 4474
                   ipv4 address 
                  8.
                  1.0.1 255.255.0.0
                   ipv4 directed-broadcast
                   ipv4 bgp policy accounting input source-accounting destination-accounting
                   ipv4 bgp policy accounting output source-accounting destination-accounting
                   GigabitEthernet
                    crc 32
                   !
                   keepalive disable
                  !
                  

                  Configure controller:

                  controller GigabitEthernet 0/0/0/4
                   ais-shut
                   path
                    ais-shut
                   !
                   threshold sf-ber 5
                  !
                  controller SONET0/0/0/8
                   ais-shut
                   path
                    ais-shut
                   !
                   threshold sf-ber 5
                  !
                  

                  Configure AS-path-set and prefix-set:

                  as-path-set as107
                    ios-regex '107$'
                  end-set
                  
                  as-path-set as108
                    ios-regex '108$'
                  end-set
                  
                  prefix-set RT-65.0
                    65.0.0.0/16 ge 16 le 32
                  end-set
                  
                  prefix-set RT-66.0
                    66.0.0.0/16 ge 16 le 32
                  end-set
                  

                  Configure the route-policy (table-policy) to set up the traffic indexes based on each prefix, AS-path-set, and prefix-set:

                  route-policy bpa1
                  
                    if destination in  (
                  27.1.1.0/24) then
                      set traffic-index 1
                    elseif destination in  (
                  27.1.2.0/24) then
                      set traffic-index 2
                    elseif destination in  (
                  27.1.3.0/24) then
                      set traffic-index 3
                    elseif destination in  (
                  27.1.4.0/24) then
                      set traffic-index 4
                    elseif destination in  (
                  27.1.5.0/24) then
                      set traffic-index 5
                    endif
                  
                    if destination in  (
                  28.1.1.0/24) then
                      set traffic-index 6
                    elseif destination in  (
                  28.1.2.0/24) then
                      set traffic-index 7
                    elseif destination in  (
                  28.1.3.0/24) then
                      set traffic-index 8
                    elseif destination in  (
                  28.1.4.0/24) then
                      set traffic-index 9
                    elseif destination in  (
                  28.1.5.0/24) then
                      set traffic-index 10
                    endif
                  
                    if as-path in as107 then
                         set traffic-index 7
                    elseif as-path in as108 then
                         set traffic-index 8
                    endif
                  
                    if destination in RT-65.0 then
                       set traffic-index 15
                    elseif destination in RT-66.0 then
                       set traffic-index 16
                    endif
                  
                  end-policy
                  

                  Configure the regular BGP route-policy to pass or drop all the BGP routes:

                  route-policy drop-all
                    drop
                  end-policy
                  !
                  route-policy pass-all
                    pass
                  end-policy
                  !
                  

                  Configure the BGP router and apply the table-policy to the global ipv4 address family:

                  router bgp 100
                   bgp router-id Loopback1
                   bgp graceful-restart
                   bgp as-path-loopcheck
                   address-family ipv4 unicast
                    table-policy bpa1
                    maximum-paths 8
                    bgp dampening
                   !
                  

                  Configure the BGP neighbor-group:

                  neighbor-group ebgp-peer-using-int-addr
                    address-family ipv4 unicast
                     policy pass-all in
                     policy drop-all out
                    !
                   !
                   neighbor-group ebgp-peer-using-int-addr-121
                    remote-as 121
                    address-family ipv4 unicast
                     policy pass-all in
                     policy drop-all out
                    !
                   !
                   neighbor-group ebgp-peer-using-int-addr-pass-out
                    address-family ipv4 unicast
                     policy pass-all in
                     policy pass-all out
                    !
                   !
                  

                  Configure BGP neighbors:

                  neighbor 
                  4.
                  1.0.2
                    remote-as 107
                    use neighbor-group ebgp-peer-using-int-addr
                   !
                   neighbor 
                  8.
                  1.0.2
                    remote-as 108
                    use neighbor-group ebgp-peer-using-int-addr
                   !
                   neighbor 
                  17.
                  1.0.2
                    use neighbor-group ebgp-peer-using-int-addr-121
                   !
                   neighbor 
                  17.1.
                  1.2
                    use neighbor-group ebgp-peer-using-int-addr-121
                   !
                  neighbor 
                  18.
                  1.0.2
                    remote-as 122
                    use neighbor-group ebgp-peer-using-int-addr
                   !
                   neighbor 
                  18.
                  1.1.2
                    remote-as 1221
                    use neighbor-group ebgp-peer-using-int-addr
                   !
                  end
                  

                  Verifying BGP Policy Statistics: Example

                  The following example shows how to verify the traffic index setup for each BGP prefix and BGP Policy Accounting statistics on ingress and egress interfaces. The following traffic stream is configured for this example:

                  • Traffic comes in from GigabitEthernet 0/2/0/4 and goes out to 5 VLAN subinterfaces under GigabitEthernet 0/2/0/2
                  • Traffic comes in from GigabitEthernet 0/0/08 and goes out to GigabitEthernet 0/0/0/4
                  show cef ipv4 interface GigabitEthernet 0/0/0/8 bgp-policy-statistics
                  
                  GigabitEthernet0/0/0/8 is up 
                  Input BGP policy accounting on dst IP address enabled
                    buckets      packets       bytes
                    7            5001160   500116000
                    15          10002320  1000232000
                  Input BGP policy accounting on src IP address enabled
                    buckets      packets       bytes
                    8            5001160   500116000
                    16          10002320  1000232000
                  Output BGP policy accounting on dst IP address enabled
                    buckets      packets       bytes
                    0                 15         790
                  Output BGP policy accounting on src IP address enabled
                    buckets      packets       bytes
                    0                 15         790
                  
                  show cef ipv4 interface GigabitEthernet 0/0/0/4 bgp-policy-statistics
                  
                  GigabitEthernet0/0/0/4 is up 
                  Input BGP policy accounting on dst IP address enabled
                    buckets      packets       bytes
                  Input BGP policy accounting on src IP address enabled
                    buckets      packets       bytes
                  Output BGP policy accounting on dst IP address enabled
                    buckets      packets       bytes
                    0                 13         653
                    7            5001160   500116000
                    15          10002320  1000232000
                  Output BGP policy accounting on src IP address enabled
                    buckets      packets       bytes
                    0                 13         653
                    8            5001160   500116000
                    16          10002320  1000232000
                  
                  show cef ipv4 interface GigabitEthernet 0/2/0/4 bgp-policy-statistics 
                  
                  GigabitEthernet0/2/0/4 is up 
                  Input BGP policy accounting on dst IP address enabled
                    buckets      packets       bytes
                    1            3297102   329710200
                    2            3297102   329710200
                    3            3297102   329710200
                    4            3297101   329710100
                    5            3297101   329710100
                  Input BGP policy accounting on src IP address enabled
                    buckets      packets       bytes
                    6            3297102   329710200
                    7            3297102   329710200
                    8            3297102   329710200
                    9            3297101   329710100
                    10           3297101   329710100
                  Output BGP policy accounting on dst IP address enabled
                    buckets      packets       bytes
                    0                 15         733
                  Output BGP policy accounting on src IP address enabled
                    buckets      packets       bytes
                    0                 15         733
                  
                  show cef ipv4 interface GigabitEthernet 0/2/0/2.1 bgp-policy-statistics
                  
                  GigabitEthernet 0/2/0/2.1 is up 
                  Input BGP policy accounting on dst IP address enabled
                    buckets      packets       bytes
                  Input BGP policy accounting on src IP address enabled
                    buckets      packets       bytes
                  Output BGP policy accounting on dst IP address enabled
                    buckets      packets       bytes
                    0                 15         752
                    1            3297102   329710200
                    2            3297102   329710200
                    3            3297102   329710200
                    4            3297101   329710100
                    5            3297101   329710100
                  Output BGP policy accounting on src IP address enabled
                    buckets      packets       bytes
                    0                 15         752
                    6            3297102   329710200
                    7            3297102   329710200
                    8            3297102   329710200
                    9            3297101   329710100
                    10           3297101   329710100
                  

                  The following example show how to verify BGP routes and traffic indexes:

                  show route bgp
                  
                  B 
                     27.1.1.0/24 [20/0] via 
                  17.
                  1.1.2, 00:07:09
                        Traffic Index 1
                  
                  B    27.1.2.0/24 [20/0] via 
                  17.
                  1.1.2, 00:07:09
                        Traffic Index 2
                  B    
                  27.1.3.0/24 [20/0] via 
                  17.
                  1.1.2, 00:07:09
                        Traffic Index 3
                  B    
                  27.1.4.0/24 [20/0] via 
                  17.
                  1.1.2, 00:07:09
                        Traffic Index 4
                  B    
                  27.1.5.0/24 [20/0] via 
                  17.
                  1.1.2, 00:07:09
                        Traffic Index 5
                  B    
                  28.
                  1.1.0/24 [20/0] via 
                  18.
                  1.1.2, 00:07:09
                        Traffic Index 6
                  B    
                  28.
                  1.2.0/24 [20/0] via 
                  18.
                  1.1.2, 00:07:09
                        Traffic Index 7
                  B    
                  28.
                  1.3.0/24 [20/0] via 
                  18.
                  1.1.2, 00:07:09
                        Traffic Index 8
                  B    
                  28.
                  1.4.0/24 [20/0] via 
                  18.
                  1.1.2, 00:07:09
                        Traffic Index 9
                  B    
                  28.
                  1.5.0/24 [20/0] via 
                  18.
                  1.1.2, 00:07:09
                        Traffic Index 10
                  B    
                  65.
                  0.1.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 15
                  B    
                  65.
                  0.2.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 15
                  B    
                  65.
                  0.3.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 15
                  B    
                  65.
                  0.
                  4.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 15
                  B    
                  65.
                  0.5.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 15
                  B    
                  65.
                  0.6.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 15
                  B    
                  65.
                  0.7.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 15
                  B    
                  65.
                  0.8.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 15
                  B    
                  65.
                  0.9.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 15
                  B    
                  65.
                  0.10.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 15
                  B    
                  66.
                  0.1.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 16
                  B    
                  66.
                  0.2.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 16
                  B    
                  66.
                  0.3.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 16
                  B    
                  66.
                  0.4.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 16
                  B    
                  66.
                  0.5.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 16
                  B    
                  66.
                  0.6.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 16
                  B    
                  66.
                  0.7.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 16
                  B    
                  66.
                  0.8.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 16
                  B    
                  66.
                  0.9.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 16
                  B    
                  66.
                  0.10.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 16
                  B    
                  67.
                  0.1.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 7
                  B    
                  67.
                  0.2.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 7
                  B    
                  67.
                  0.3.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 7
                  B    
                  67.
                  0.4.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 7
                  B    
                  67.
                  0.5.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 7
                  B 
                     67.
                  0.6.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 7
                  B 
                     67.
                  0.7.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 7
                  B 
                     67.
                  0.8.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 7
                  B 
                     67.
                  0.9.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 7
                  B 
                     67.
                  0.10.0/24 [20/0] via 
                  4.
                  1.0.2, 00:07:09
                        Traffic Index 7
                  B    
                  68.
                  0.1.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 8
                  B 
                     68.
                  0.2.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 8
                  B 
                     68.
                  0.3.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 8
                  B 
                     68.
                  0.4.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 8
                  B 
                     68.
                  0.5.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 8
                  B 
                     68.
                  0.6.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 8
                  B 
                     68.
                  0.7.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 8
                  B 
                     68.
                  0.8.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 8
                  B 
                     68.
                  0.9.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 8
                  B 
                     68.
                  0.10.0/24 [20/0] via 
                  8.
                  1.0.2, 00:07:09
                        Traffic Index 8
                  
                  show bgp summary
                  
                  BGP router identifier 
                  190.
                  1.
                  1.
                  1, local AS number 100
                  BGP generic scan interval 60 secs
                  BGP main routing table version 151
                  Dampening enabled
                  BGP scan interval 60 secs
                  BGP is operating in STANDALONE mode.
                  
                  Process         RecvTblVer    bRIB/RIB  SendTblVer
                  Speaker                151         151         151
                  
                  Neighbor        Spk    AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  St/PfxRcd
                  
                  4.
                  1.0.2           0   107      54      53      151    0    0 00:25:26       20
                  
                  8.1.0.2           0   108      54      53      151    0    0 00:25:28       20
                  
                  17.1.0.2          0   121      53      54      151    0    0 00:25:42        0
                  
                  17.1.1.2          0   121      53      53      151    0    0 00:25:06        5
                  
                  17.1.2.2          0   121      52      54      151    0    0 00:25:04        0
                  
                  17.1.3.2          0   121      52      53      151    0    0 00:25:26        0
                  
                  17.1.4.2          0   121      53      54      151    0    0 00:25:41        0
                  
                  17.1.5.2          0   121      53      54      151    0    0 00:25:43        0
                  
                  17.1.6.2          0   121      51      53      151    0    0 00:24:59        0
                  
                  17.1.7.2          0   121      51      52      151    0    0 00:24:44        0
                  
                  17.1.8.2          0   121      51      52      151    0    0 00:24:49        0
                  
                  18.
                  1.0.2          0   122      52      54      151    0    0 00:25:21        0
                  
                  18.
                  1.1.2          0  1221      54      54      151    0    0 00:25:43        5
                  
                  18.
                  1.2.2          0  1222      53      54      151    0    0 00:25:38        0
                  
                  18.
                  1.3.2          0  1223      52      53      151    0    0 00:25:17        0
                  
                  18.
                  1.4.2          0  1224      51      52      151    0    0 00:24:57        0
                  
                  18.
                  1.5.2          0  1225      52      53      151    0    0 00:25:14        0
                  
                  18.
                  1.6.2          0  1226      52      54      151    0    0 00:25:04        0
                  
                  18.
                  1.7.2          0  1227      52      54      151    0    0 00:25:13        0
                  
                  18.
                  1.8.2          0  1228      53      54      151    0    0 00:25:36        0
                  
                  show bgp 27.1.1.1
                  
                  BGP routing table entry for 27.1.1.0/24
                  Versions:
                    Process           bRIB/RIB  SendTblVer
                    Speaker                102         102
                  Paths: (1 available, best #1)
                    Not advertised to any peer
                    Received by speaker 0
                    121
                      
                  17.1.1.2 from 
                  17.1.1.2 (
                  17.1.1.2)
                        Origin incomplete, localpref 100, valid, external, best
                        Community: 27:1 121:1
                  
                  show bgp 
                  28.1.1.1
                  
                  BGP routing table entry for 
                  28.1.1.0/24
                  Versions:
                    Process           bRIB/RIB  SendTblVer
                    Speaker                107         107
                  Paths: (1 available, best #1)
                    Not advertised to any peer
                    Received by speaker 0
                    1221
                  
                      18.
                  1.1.2 from 
                  18.
                  1.1.2 (18.1.1.2)
                        Origin incomplete, localpref 100, valid, external, best
                        Community: 28:1 1221:1
                  
                  show bgp 
                  65.0.1.1
                  
                  BGP routing table entry for 
                  65.0.1.0/24
                  Versions:
                    Process           bRIB/RIB  SendTblVer
                    Speaker                112         112
                  Paths: (1 available, best #1)
                    Not advertised to any peer
                    Received by speaker 0
                    107
                      
                  4.1.0.2 from 
                  4.1.0.2 (
                  4.1.0.2)
                        Origin incomplete, localpref 100, valid, external, best
                        Community: 107:65
                  
                  show bgp 
                  66.
                  0.1.1
                  
                  BGP routing table entry for 
                  66.
                  0.1.0/24
                  Versions:
                    Process           bRIB/RIB  SendTblVer
                    Speaker                122         122
                  Paths: (1 available, best #1)
                    Not advertised to any peer
                    Received by speaker 0
                    108
                      8.1.0.2 from 8.1.0.2 (8.1.0.2)
                        Origin incomplete, localpref 100, valid, external, best
                        Community: 108:66
                  
                  show bgp 67.0.1.1
                  
                  BGP routing table entry for 67.0.1.0/24
                  Versions:
                    Process           bRIB/RIB  SendTblVer
                    Speaker                132         132
                  Paths: (1 available, best #1)
                    Not advertised to any peer
                    Received by speaker 0
                    107
                      4.1.0.2 from 4.1.0.2 (4.1.0.2)
                        Origin incomplete, localpref 100, valid, external, best
                        Community: 107:67
                  
                  show bgp 68.0.1.1
                  
                  BGP routing table entry for 68.0.1.0/24
                  Versions:
                    Process           bRIB/RIB  SendTblVer
                    Speaker                142         142
                  Paths: (1 available, best #1)
                    Not advertised to any peer
                    Received by speaker 0
                    108
                      8.1.0.2 from 8.1.0.2 (8.1.0.2)
                        Origin incomplete, localpref 100, valid, external, best
                        Community: 108:68
                  
                  show route ipv4 27.1.1.1
                  
                  Routing entry for 27.1.1.0/24
                    Known via "bgp 100", distance 20, metric 0
                    Tag 121, type external, Traffic Index 1
                    Installed Nov 11 21:14:05.462
                    Routing Descriptor Blocks
                      17.1.1.2, from 17.1.1.2
                        Route metric is 0
                    No advertising protos. 
                  
                  show route ipv4 28.1.1.1
                  
                  Routing entry for 28.1.1.0/24
                    Known via "bgp 100", distance 20, metric 0
                    Tag 1221, type external, Traffic Index 6
                    Installed Nov 11 21:14:05.462
                    Routing Descriptor Blocks
                      18.1.1.2, from 18.1.1.2
                        Route metric is 0
                    No advertising protos. 
                  
                  show route ipv4 65.0.1.1
                  
                  Routing entry for 65.0.1.0/24
                    Known via "bgp 100", distance 20, metric 0
                    Tag 107, type external, Traffic Index 15
                    Installed Nov 11 21:14:05.462
                    Routing Descriptor Blocks
                      4.1.0.2, from 4.1.0.2
                        Route metric is 0
                    No advertising protos. 
                  
                  show route ipv4 66.0.1.1
                  
                  Routing entry for 66.0.1.0/24
                    Known via "bgp 100", distance 20, metric 0
                    Tag 108, type external, Traffic Index 16
                    Installed Nov 11 21:14:05.462
                    Routing Descriptor Blocks
                      8.1.0.2, from 8.1.0.2
                        Route metric is 0
                    No advertising protos. 
                  
                  show route ipv4 67.0.1.1
                  
                  Routing entry for 67.0.1.0/24
                    Known via "bgp 100", distance 20, metric 0
                    Tag 107, type external, Traffic Index 7
                    Installed Nov 11 21:14:05.462
                    Routing Descriptor Blocks
                      4.1.0.2, from 4.1.0.2
                        Route metric is 0
                    No advertising protos. 
                  
                  show route ipv4 68.0.1.1
                  
                  Routing entry for 68.0.1.0/24
                    Known via "bgp 100", distance 20, metric 0
                    Tag 108, type external, Traffic Index 8
                    Installed Nov 11 21:14:05.462
                    Routing Descriptor Blocks
                      8.1.0.2, from 8.1.0.2
                        Route metric is 0
                    No advertising protos. 
                  
                  show cef ipv4 27.1.1.1
                  
                  27.1.1.0/24, version 263, source-destination sharing
                  Prefix Len 24, Traffic Index 1, precedence routine (0)
                    via 17.1.1.2, 0 dependencies, recursive
                      next hop 17.1.1.2/24, GigabitEthernet 0/2/0/2.1 via 17.1.1.0/24
                      valid remote adjacency
                    Recursive load sharing using 17.1.1.0/24
                  
                  show cef ipv4 28.1.1.1
                  
                  28.1.1.0/24, version 218, source-destination sharing
                  Prefix Len 24, Traffic Index 6, precedence routine (0)
                    via 18.1.1.2, 0 dependencies, recursive
                      next hop 18.1.1.2/24, GigabitEthernet0/2/0/4.1 via 18.1.1.0/24
                      valid remote adjacency
                    Recursive load sharing using 18.1.1.0/24
                  
                  show cef ipv4 65.0.1.1
                  
                  65.0.1.0/24, version 253, source-destination sharing
                  Prefix Len 24, Traffic Index 15, precedence routine (0)
                    via 4.1.0.2, 0 dependencies, recursive
                      next hop 4.1.0.2/16, GigabitEthernet0/0/0/4 via 4.1.0.0/16
                      valid remote adjacency
                    Recursive load sharing using 4.1.0.0/16
                  
                  show cef ipv4 66.0.1.1
                  
                  66.0.1.0/24, version 233, source-destination sharing
                  Prefix Len 24, Traffic Index 16, precedence routine (0)
                    via 8.1.0.2, 0 dependencies, recursive
                      next hop 8.1.0.2/16, GigabitEthernet 0/0/0/8 via 8.1.0.0/16
                      valid remote adjacency
                    Recursive load sharing using 8.1.0.0/16
                  
                  show cef ipv4 67.0.1.1
                  
                  67.0.1.0/24, version 243, source-destination sharing
                  Prefix Len 24, Traffic Index 7, precedence routine (0)
                    via 4.1.0.2, 0 dependencies, recursive
                      next hop 4.1.0.2/16, GigabitEthernet 0/0/0/4 via 4.1.0.0/16
                      valid remote adjacency
                    Recursive load sharing using 4.1.0.0/16
                  
                  show cef ipv4 68.0.1.1
                  
                  68.0.1.0/24, version 223, source-destination sharing
                  Prefix Len 24, Traffic Index 8, precedence routine (0)
                    via 8.1.0.2, 0 dependencies, recursive
                      next hop 8.1.0.2/16, GigabitEthernet0/0/0/8 via 8.1.0.0/16
                      valid remote adjacency
                    Recursive load sharing using 8.1.0.0/16
                  
                  show cef ipv4 27.1.1.1 detail
                  
                  27.1.1.0/24, version 263, source-destination sharing
                  Prefix Len 24, Traffic Index 1, precedence routine (0)
                    via 17.1.1.2, 0 dependencies, recursive
                      next hop 17.1.1.2/24, GigabitEthernet 0/2/0/2.1 via 17.1.1.0/24
                      valid remote adjacency
                  
                    Recursive load sharing using 17.1.1.0/24
                    Load distribution: 0 (refcount 6)
                  
                    Hash  OK  Interface                 Address  Packets
                    1     Y   GigabitEthernet 0/2/0/2.1          (remote)               0
                  
                  show cef ipv4 28.1.1.1 detail
                  
                  28.1.1.0/24, version 218, source-destination sharing
                  Prefix Len 24, Traffic Index 6, precedence routine (0)
                    via 18.1.1.2, 0 dependencies, recursive
                      next hop 18.1.1.2/24, GigabitEthernet 0/2/0/4.1 via 18.1.1.0/24
                      valid remote adjacency
                  
                    Recursive load sharing using 18.1.1.0/24
                    Load distribution: 0 (refcount 6)
                  
                    Hash  OK  Interface                 Address  Packets
                    1     Y   GigabitEthernet 0/2/0/4.1          (remote)               0
                  
                  show cef ipv4 65.0.1.1 detail
                  
                  65.0.1.0/24, version 253, source-destination sharing
                  Prefix Len 24, Traffic Index 15, precedence routine (0)
                    via 4.1.0.2, 0 dependencies, recursive
                      next hop 4.1.0.2/16, GigabitEthernet0/0/0/4 via 4.1.0.0/16
                      valid remote adjacency
                  
                    Recursive load sharing using 4.1.0.0/16
                    Load distribution: 0 (refcount 21)
                  
                    Hash  OK  Interface                 Address  Packets
                    1     Y   GigabitEthernet0/0/0/4                (remote)               0
                  
                  show cef ipv4 66.0.1.1 detail
                  
                  66.0.1.0/24, version 233, source-destination sharing
                  Prefix Len 24, Traffic Index 16, precedence routine (0)
                    via 8.1.0.2, 0 dependencies, recursive
                      next hop 8.1.0.2/16, GigabitEthernet0/0/0/8 via 8.1.0.0/16
                      valid remote adjacency
                  
                    Recursive load sharing using 8.1.0.0/16
                    Load distribution: 0 (refcount 21)
                  
                    Hash  OK  Interface                 Address  Packets
                    1     Y   GigabitEthernet 0/0/0/8                (remote)               0
                  
                  show cef ipv4 67.0.1.1 detail
                  
                  67.0.1.0/24, version 243, source-destination sharing
                  Prefix Len 24, Traffic Index 7, precedence routine (0)
                    via 4.1.0.2, 0 dependencies, recursive
                      next hop 4.1.0.2/16, GigabitEthernet 0/0/0/4 via 4.1.0.0/16
                      valid remote adjacency
                  
                    Recursive load sharing using 4.1.0.0/16
                    Load distribution: 0 (refcount 21)
                  
                    Hash  OK  Interface                 Address  Packets
                    1     Y   GigabitEthernet 0/0/0/4                (remote)               0
                  
                  show cef ipv4 68.0.1.1 detail
                  
                  68.0.1.0/24, version 223, source-destination sharing
                  Prefix Len 24, Traffic Index 8, precedence routine (0)
                    via 8.1.0.2, 0 dependencies, recursive
                      next hop 8.1.0.2/16, GigabitEthernet 0/0/0/8 via 8.1.0.0/16
                      valid remote adjacency
                  
                    Recursive load sharing using 8.1.0.0/16
                    Load distribution: 0 (refcount 21)
                  
                    Hash  OK  Interface                 Address  Packets
                    1     Y   GigabitEthernet 0/0/0/8                (remote)               0
                  

                  Configuring Unicast RPF Checking: Example

                  The following example shows how to configure unicast RPF checking:

                  configure
                  interface GigabitEthernet 0/0/0/1
                  ipv4 verify unicast source reachable-via rx
                  end
                  

                  Configuring the Switching of Modular Services Card to Management Ethernet Interfaces on the Route Processor: Example

                  The following example shows how to configure the switching of the MSC to Management Ethernet interfaces on the route processor:

                  configure
                  rp mgmtethernet forwarding
                  end
                  

                  Configuring Per-Flow Load Balancing: Example

                  The following examples show how to configure Layer 3 and Layer 4 load-balancing for the hash algorithm from the cef load-balancing fields command, and how to verify summary information for the CEF table from the show cef summary command:

                  Configuring Layer 3 load-balancing

                  configure
                   cef load-balancing fields L3 
                   end
                   !
                  show cef summary
                  Router ID is 10.6.6.6
                  
                  IP CEF with switching (Table Version 0) for node0_0_CPU0
                  
                    Load balancing: L3
                    Tableid 0xe0000000 (0x9cbb51b0), Vrfid 0x60000000, Vrid 0x20000000, Flags 0x2031
                    Vrfname default, Refcount 577
                    300 routes, 0 protected, 0 reresolve, 0 unresolved (0 old, 0 new), 21600 bytes
                    212 load sharing elements, 62576 bytes, 324 references
                    19 shared load sharing elements, 5388 bytes
                    193 exclusive load sharing elements, 57188 bytes
                    
                    622 local route bufs received, 1 remote route bufs received,  0 mix bufs received
                    176 local routes, 0 remote routes
                    4096 total local route updates processed
                    0 total remote route updates processed 
                    0 pkts pre-routed to cust card
                  
                    0 pkts received from core card
                    0 CEF route update drops, 96 revisions of existing leaves
                    0 CEF route update drops due to version mis-match
                    Resolution Timer: 15s
                    0 prefixes modified in place
                    0 deleted stale prefixes
                    82 prefixes with label imposition, 107 prefixes with label information
                   95 next hops
                    0 incomplete next hops
                  
                  0 PD backwalks on LDIs with backup path
                  
                  

                  Configuring Layer 4 load-balancing

                  
                  configure
                   cef load-balancing fields L4
                   end
                   !
                  show cef summary
                  
                  Router ID is 
                  10
                  1.1.1.101
                  
                  IP CEF with switching (Table Version 0) for node0_RP0_CPU0
                  
                    Load balancing: L4
                    Tableid 0xe0000000, Vrfid 0x60000000, Vrid 0x20000000, Flags 0x301
                    Vrfname default, Refcount 286242
                    286122 routes, 0 reresolve, 0 unresolved (0 old, 0 new), 20600784 bytes
                    11124 load sharing elements, 3014696 bytes, 297064 references
                    8 shared load sharing elements, 3008 bytes
                    11116 exclusive load sharing elements, 3011688 bytes
                    0 CEF route update drops, 3900571 revisions of existing leaves
                    Resolution Timer: 15s
                    0 prefixes modified in place
                    0 deleted stale prefixes
                    0 prefixes with label imposition, 11032 prefixes with label information Adjacency Table has 15 adjacencies
                    1 incomplete adjacency
                  
                  

                  Configuring BGP Attributes Download: Example

                  The following example shows how to configure the BGP Attributes Download feature:

                  router configure
                  show cef bgp attribute {attribute-id| local-attribute-id}
                  

                  Additional References

                  The following sections provide references related to implementing CEF.

                  Related Documents

                  Related Topic

                  Document Title

                  CEF commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples

                  Cisco Express Forwarding Commands module in Cisco IOS XR IP Addresses and Services Command Reference for the Cisco XR 12000 Series Router

                  BGP commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples

                  BGP Commands module in the Cisco IOS XR Routing Command Reference for the Cisco XR 12000 Series Router

                  Link Bundling Commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples

                  Link Bundling Commands module in the Cisco IOS XR Interface and Hardware Component Command Reference for the Cisco XR 12000 Series Router

                  Standards

                  Standards

                  Title

                  No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

                  MIBs

                  MIBs

                  MIBs Link

                  To locate and download MIBs, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: http:/​/​cisco.com/​public/​sw-center/​netmgmt/​cmtk/​mibs.shtml

                  RFCs

                  RFCs

                  Title

                  No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

                  Technical Assistance

                  Description

                  Link

                  The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

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