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Configuring Basic Cisco Express Forwarding for Improved Performance, Scalability, and Resiliency in Dynamic Networks

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Configuring Basic Cisco Express Forwarding for Improved Performance, Scalability, and Resiliency in Dynamic Networks

Finding Feature Information

Contents

Prerequisites for Configuring Cisco Express Forwarding

Restrictions for Configuring Cisco Express Forwarding

Information About Configuring Basic Cisco Express Forwarding

Cisco Platform Support for Cisco Express Forwarding and Distributed Cisco Express Forwarding

Cisco Express Forwarding Benefits: Improved Performance, Scalability, and Resiliency

Main Components for Cisco Express Forwarding Operation

Cisco Express Forward Operation Modes: Central and Distributed

Central Cisco Express Forwarding Mode Operation

Distributed Cisco Express Forwarding Mode Operation

How to Configure Basic Cisco Express Forwarding

How to Verify Basic Cisco Express Forwarding

Determining If the Router Is Configured for Central or Distributed Cisco Express Forwarding

What to Do Next

Verifying Cisco Express Forwarding Operation on Your Router

Verifying That Cisco Express Forwarding Switching Is Enabled on the Input Interface on the Router

Locating the Prefix in a Forwarding Table on the RP

Finding the Cisco Express Forwarding Output Information Associated with the Prefix on the RP

Verifying the Adjacency or Next-Hop Information on the RP

Verifying Distributed Cisco Express Forwarding Operation on Your Router

Syntax for Cisco Express Forwarding Commands on Line Cards

Verifying That Distributed Cisco Express Forwarding Switching Is Enabled on the Input Interface on a Line Card

Locating the Prefix in a Forwarding Table on a Line Card

Finding the Distributed Cisco Express Forwarding Output Information Associated with the Prefix on a Line Card

Verifying the Adjacency or Next-Hop Information on a Line Card

Interpreting Information in Cisco Express Forwarding Command Output

Verifying That the Cisco Express Forwarding Information Looks As Expected

Interpreting MPLS Information in Cisco Express Forwarding Output

Configuration Examples for Basic Cisco Express Forwarding

Where to Go Next

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Configuring Basic Cisco Express Forwarding

Glossary


Configuring Basic Cisco Express Forwarding for Improved Performance, Scalability, and Resiliency in Dynamic Networks

First Published: May 2, 2005
Last Updated: July 23, 2010

This module contains information about Cisco Express Forwarding and describes the required and optional tasks for verifying Cisco Express Forwarding and distributed Cisco Express Forwarding operation.

Cisco Express Forwarding is an advanced Layer 3 IP switching technology. It optimizes network performance and scalability for all kinds of networks: those that carry small amounts of traffic and those that carry large amounts of traffic in complex patterns, such as the Internet, and networks characterized by intensive web-based applications or interactive sessions.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Configuring Basic Cisco Express Forwarding" section.

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

Contents

•Prerequisites for Configuring Cisco Express Forwarding

•Restrictions for Configuring Cisco Express Forwarding

•Information About Configuring Basic Cisco Express Forwarding

•How to Configure Basic Cisco Express Forwarding

•How to Verify Basic Cisco Express Forwarding

•Configuration Examples for Basic Cisco Express Forwarding

•Where to Go Next

•Additional References

•Feature Information for Configuring Basic Cisco Express Forwarding

•Glossary

Prerequisites for Configuring Cisco Express Forwarding

Cisco Express Forwarding requires a software image that includes Cisco Express Forwarding and IP routing enabled on the device.

Restrictions for Configuring Cisco Express Forwarding

Cisco Express Forwarding has the following restrictions:

•The Cisco 12000 Series Internet routers operate only in distributed Cisco Express Forwardingmode.

•If you enable Cisco Express Forwarding and then create an access list that uses the log keyword, the packets that match the access list are not Cisco Express Forwarding switched. They are process switched. Logging disables Cisco Express Forwarding.

Information About Configuring Basic Cisco Express Forwarding

•Cisco Platform Support for Cisco Express Forwarding and Distributed Cisco Express Forwarding

•Cisco Express Forwarding Benefits: Improved Performance, Scalability, and Resiliency

•Main Components for Cisco Express Forwarding Operation

•Cisco Express Forward Operation Modes: Central and Distributed

•How to Configure Basic Cisco Express Forwarding

If your network architecture requires that you disable or reenable Cisco Express Forwarding or distributed Cisco Express Forwarding switching and forwarding, change your load balancing scheme, refresh Cisco Express Forwarding tables, configure network accounting for Cisco Express Forwarding, or customize the display of Cisco Express Forwarding events, go to the "Related Documents" section for links to information on these tasks. Otherwise, you need do nothing more to configure Cisco Express Forwarding or distributed Cisco Express Forwarding operation in your network.

Note Cisco Express Forwarding is supported on interfaces on which IEEE 802.1Q encapsulation has been enabled at the subinterface level. You no longer need to disable CEF operation on interfaces that are using IEEE 802.1Q encapsulation on VLAN subinterfaces.

Cisco Platform Support for Cisco Express Forwarding and Distributed Cisco Express Forwarding

Cisco Express Forwarding is enabled by default on most Cisco platforms running Cisco IOS software Release 12.0 and later. When Cisco Express Forwarding in enabled on a router, the Route Processor (RP) performs the express forwarding.

To find out if Cisco Express Forwarding is enabled by default on your platform, enter the show ip cef command. If Cisco Express Forwarding is enabled, you receive output that looks like the following: 

Router# show ip cef 


Prefix              Next Hop            Interface

[...]

10.2.61.8/24        192.168.100.1       FastEthernet1/0/0

                    192.168.101.1       FastEthernet6/1

[...]

If Cisco Express Forwarding is not enabled on your platform, the output for the show ip cef command looks like this: 

Router# show ip cef


%CEF not running

Distributed Cisco Express Forwarding is enabled by default on the Catalyst 6500 series switch, the Cisco 7500 series router, and the Cisco 12000 Series Internet Router. When distributed Cisco Express Forwarding is enabled on your platform, the line cards perform the express forwarding.

If Cisco Express Forwarding is not enabled on your platform, use the ip cef command to enable Cisco Express Forwarding or the ip cef distributed command to enable distributed Cisco Express Forwarding.

Cisco Express Forwarding Benefits: Improved Performance, Scalability, and Resiliency

•Improved performance—Cisco Express Forwarding is less CPU-intensive than fast switching route caching. As a result, more CPU processing power can be dedicated to Layer 3 services such as quality of service (QoS) and encryption.

•Scalability—Cisco Express Forwarding offers full switching capacity at each line card when distributed Cisco Express Forwarding mode is active. Distributed Cisco Express Forwarding is a distributed switching mechanism that scales linearly with the number of interface cards and the bandwidth installed in the router.

•Resiliency—Cisco Express Forwarding offers an unprecedented level of switching consistency and stability in large dynamic networks. In dynamic networks, fast-switched cache entries are frequently invalidated by routing changes. These changes can cause traffic to be process-switched through use of the routing table, rather than fast-switched through use of the route cache. Because the forwarding information base (FIB) lookup table contains all known routes that exist in the routing table, it eliminates the need for route cache maintenance and the steps involved with fast-switch or process-switch forwarding. Cisco Express Forwarding can switch traffic more efficiently than typical demand caching schemes.

Main Components for Cisco Express Forwarding Operation

Information conventionally stored in a route cache is stored in several data structures for Cisco Express Forwarding switching. The data structures provide optimized lookup for efficient packet forwarding. The two main components of Cisco Express Forwarding operation are the forwarding information base (FIB) and the adjacency tables.

The FIB is conceptually similar to a routing table or information base. A router uses this lookup table to make destination-based switching decisions during Cisco Express Forwarding operation. The FIB is updated as changes occur in the network and contains all routes known at the time. For more information on the FIB, see the "Cisco Express Forwarding Overview" module.

Adjacency tables maintain Layer 2 next-hop addresses for all FIB entries. For more information on adjacency tables, see the "Cisco Express Forwarding Overview" module.

This separation of the reachability information (in the Cisco Express Forwarding table) and the forwarding information (in the adjacency table), provides two main benefits:

•The adjacency table can be built separately from the Cisco Express Forwarding table, allowing both tables to build without the process switching of any packets.

•The MAC header rewrite used to forward a packet isn't stored in cache entries, so changes in a MAC header rewrite string do not require invalidation of cache entries.

Cisco Express Forward Operation Modes: Central and Distributed

•Central Cisco Express Forwarding Mode Operation

•Distributed Cisco Express Forwarding Mode Operation

Central Cisco Express Forwarding Mode Operation

You can use central Cisco Express Forwarding mode when line cards are not available for Cisco Express Forwarding switching, when you need to use features not compatible with distributed Cisco Express Forwarding switching, or when you are running on a platform that is not a distributed platform. When central Cisco Express Forwarding mode is enabled, the Cisco Express Forwarding FIB and adjacency tables reside on the RP, and the RP performs the express forwarding.

Figure 1 shows the relationship between the routing table, the FIB, and the adjacency table during central Cisco Express Forwarding mode operation. The Catalyst switches forward traffic from workgroup LANs to a Cisco 7500 series router on the enterprise backbone running central Cisco Express Forwarding. The RP performs the express forwarding.

Figure 1 Central Cisco Express Forwarding Mode Operation

Distributed Cisco Express Forwarding Mode Operation

For additional scalability, Cisco Express Forwarding runs in the form of distributed Cisco Express Forwarding on certain platforms by spreading processing tasks across two or more line cards. When distributed Cisco Express Forwarding mode is enabled, line cards maintain identical copies of the FIB and adjacency tables. The line cards perform the express forwarding between port adapters, relieving the RP of involvement in the switching operation, thus also enhancing system performance.

Distributed Cisco Express Forwarding uses an interprocess communication (IPC) mechanism to ensure synchronization of FIB tables and adjacency tables on the RP and line cards.

Figure 2 shows the relationship between the RP and line cards when distributed Cisco Express Forwarding mode is active.

Figure 2 Distributed Cisco Express Forwarding Mode Operation

In the Cisco 12000 Series Internet Router, shown in Figure 2, the line cards perform the switching. In other routers, where you can mix various types of cards in the same router, all cards might not support distributed Cisco Express Forwarding. When a line card that does not support distributed Cisco Express Forwarding receives a packet on one of these other routers, the line card forwards the packet to the next higher switching layer (the RP). This structure allows legacy interface processors to exist in the router with newer interface processors.

Note The Cisco 12000 Series Internet routers operate only in distributed Cisco Express Forwarding mode.

How to Configure Basic Cisco Express Forwarding

There are no configuration tasks. Cisco Express Forwarding is enabled by default.

How to Verify Basic Cisco Express Forwarding

The following section contains instructions for verifying basic Cisco Express Forwarding or distributed Cisco Express Forwarding operation.

Before you perform the remaining tasks in this section you need to know which mode of Cisco Express Forwarding is running on your router. Cisco Express Forwarding is enabled by default on the Cisco 7100, 7200, and 7500 series routers. Distributed Cisco Express Forwarding is enabled by default on the Catalyst 6500 switch and on Cisco 12000 Series Internet routers. To determine if Cisco Express Forwarding or distributed Cisco Express Forwarding is enabled on your router, you can enter the show ip interface command and look for the entry "IP CEF switching enabled" or "IP Distributed CEF switching enabled." If Cisco Express Forwarding is not enabled, the entry in the command display would indicate that "IP CEF switching is disabled."

To verify basic Cisco Express Forwarding or distributed Cisco Express Forwarding operation, perform the following procedures and tasks:

•Determining If the Router Is Configured for Central or Distributed Cisco Express Forwarding (required)

•Verifying Cisco Express Forwarding Operation on Your Router (optional)

•Verifying Distributed Cisco Express Forwarding Operation on Your Router (optional)

•Interpreting Information in Cisco Express Forwarding Command Output (optional)

Determining If the Router Is Configured for Central or Distributed Cisco Express Forwarding

To determine if the router is configured for Cisco Express Forwarding or distributed Cisco Express Forwarding, perform the following task.

SUMMARY STEPS

1. enable

2. show ip interface [type number] [brief]

3. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

show ip interface [type number] [brief]

Example:

Router# show ip interface

Displays the usability status of interfaces configured for IP.

•The type argument is the interface type.

•The number argument is the interface number.

•The brief keyword displays a summary of the usability status information.

Look for the entry "IP CEF switching enabled" or "IP Distributed CEF switching enabled."

Step 3 

exit

Example:

Router# exit

Exits to user EXEC mode.

What to Do Next

•If the router is configured for Cisco Express Forwarding, complete the steps in each of the tasks on the RP in the "Verifying Cisco Express Forwarding Operation on Your Router" section.

•If the router is configured for distributed Cisco Express Forwarding, complete the steps in each of the tasks on the line card in the "Verifying Distributed Cisco Express Forwarding Operation on Your Router" section. You might also need to complete steps, as indicated in each task, on the RP. By performing the same steps on the RP that you do on the line cards, you can verify that the forwarding tables on the RP and the line cards are synchronized.

Verifying Cisco Express Forwarding Operation on Your Router

Perform the following tasks, in the order presented, to verify Cisco Express Forwarding operation on your router or to look for Cisco Express Forwarding operation information on your router:

•Verifying That Cisco Express Forwarding Switching Is Enabled on the Input Interface on the Router

•Locating the Prefix in a Forwarding Table on the RP

•Finding the Cisco Express Forwarding Output Information Associated with the Prefix on the RP

•Verifying the Adjacency or Next-Hop Information on the RP

See the "Verifying Distributed Cisco Express Forwarding Operation on Your Router" section for the tasks to perform for d istributed Cisco Express Forwarding operation.

Verifying That Cisco Express Forwarding Switching Is Enabled on the Input Interface on the Router

To verify tha Cisco Express Forwarding switching is enabled on the input (ingress) interface on the router, perform the following steps.

SUMMARY STEPS

1. enable

2. show ip cef

3. show cef interface type number detail

4. show ip interface type number

5. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. You can also enter this command in user EXEC mode. Enter your password if prompted. For example: 

Router> enable

Router#

Step 2 show ip cef

Use this command to verify that Cisco Express Forwarding is enabled globally. For example: 

Router# show ip cef


%CEF not running

If Cisco Express Forwarding is not running, use the ip cef command to enable Cisco Express Forwarding or the ip cef distributed command to enable distributed Cisco Express Forwarding.

When Cisco Express Forwarding or distributed Cisco Express Forwarding is enabled, the show ip cef command shows a brief display of all FIB entries.

Step 3 show cef interface type number detail

Use this command to verify that Cisco Express Forwarding is enabled on a particular ingress interface. Look for the entry "IP CEF switching enabled." For example: 

Router# show cef interface fastethernet 1/0/0 detail


FastEthernet1/0/0 is up (if_number 9)

  Corresponding hwidb fast_if_number 9

  Corresponding hwidb firstsw->if_number 9

  Internet address is 10.2.61.8/24

  ICMP redirects are always sent

  Per packet load-sharing is disabled

  IP unicast RPF check is disabled

  Inbound access list is not set

  Outbound access list is not set

  IP policy routing is disabled

  Hardware idb is FastEthernet1/0/0

  Fast switching type 1, interface type 5

  IP CEF switching enabled

  IP Feature Fast switching turbo vector

  IP Feature CEF switching turbo vector

  Input fast flags 0x0, Output fast flags 0x0

  ifindex 7(7)

  Slot 1 Slot unit 0 VC -1

  Transmit limit accumulator 0x48001A82 (0x48001A82)

  IP MTU 1500

Step 4 show ip interface type number

Use this command to display the Cisco IOS switching methods enabled on an interface. For example: 

router# show ip interface fastethernet 1/0/0 


 FastEthernet1/0/0 is up, line protocol is up 

   IP fast switching is enabled 

   IP fast switching on the same interface is enabled 

   IP Flow switching is disabled 

   IP CEF switching is enabled 

   IP Distributed switching is enabled 

   IP Fast switching turbo vector 

   IP Normal CEF switching turbo vector 

   IP multicast fast switching is enabled 

   IP multicast distributed fast switching is disabled 

   IP route-cache flags are Fast, Distributed, No CEF

In the above output, the "IP CEF switching is enabled" entry indicates that Cisco Express Forwarding is enabled by default. The "No CEF" IP route-cache flag indicates that Cisco Express Forwarding is disabled because an administrator entered the no ip route-cache cef command on this interface.

To enable Cisco Express Forwarding on this interface, enter the ip route-cache cef command. Once you do that, the "CEF" flag indicates that Cisco Express Forwarding is running.

Step 5 exit

Use this command to exit privileged EXEC mode. For example: 

Router# exit

Router>

Locating the Prefix in a Forwarding Table on the RP

To locate the prefix in a forwarding table, perform the following steps.

SUMMARY STEPS

1. enable

2. show ip cef

3. show ip cef vrf vrf-name

4. Repeat Step 2 as many times as required to locate the prefix.

5. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. You can also enter this command in user EXEC mode. Enter your password if prompted. For example: 

Router> enable

Router#

Step 2 show ip cef

Use this command to show entries in the FIB and confirm that prefixes are listed in the FIB. For example: 

Router# show ip cef 


Prefix              Next Hop            Interface

[...]

10.2.61.8/24        192.168.100.1       FastEthernet1/0/0

                    192.168.101.1       FastEthernet6/1

[...]

Step 3 show ip cef vrf vrf-name

Use this command to locate prefixes in forwarding tables associated with Virtual Private Network (VPN) routing/forwarding table instances (VRFs). For example, this command shows prefixes in the left-hand column for a VRF named vpn1: 

Router# show ip cef vrf vpn1


Prefix              Next Hop            Interface

0.0.0.0/32          receive

10.1.0.0/8          10.0.0.1            Ethernet1/3

10.2.0.0/8          10.0.0.2            POS6/0

10.0.0.0/8          attached            Ethernet1/3

10.0.0.0/32         receive

10.0.0.1/32         10.0.0.1            Ethernet1/3

10.0.0.2/32         receive

10.255.255.255/32   receive

10.3.0.0/8          10.0.0.2            POS6/0

10.50.0.0/24        receive

255.255.255.255/32  receive

Step 4 Repeat Step 2 as many times as required to locate the prefix.

If Cisco Express Forwarding is in a VPN, you might need to look at multiple VRFs.

Step 5 exit

Use this command to exit privileged EXEC mode. For example: 

Router# exit

Router>

Finding the Cisco Express Forwarding Output Information Associated with the Prefix on the RP

To find the Cisco Express Forwarding output information associated with the prefix on the RP, perform the following steps.

SUMMARY STEPS

1. enable

2. show ip cef

3. show ip cef prefix

4. show ip cef prefix detail

5. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. You can also enter this command in user EXEC mode. Enter your password if prompted. For example: 

Router> enable

Router#

Step 2 show ip cef

Use this command to confirm that the prefix is listed in the FIB. For example: 

router# show ip cef


Prefix              Next Hop            Interface 

0.0.0.0/32          receive 

192.168.0.0/30      attached            Serial2/0/0:1 

192.168.0.0/32      receive

10.2.61.8/24        192.168.100.1       FastEthernet1/0/0

Step 3 show ip cef prefix

Use this command to display the prefix entry in the FIB for centralized Cisco Express Forwarding. For example: 

Router# show ip cef 10.2.61.8 255.255.255.0


10.0.0.0/8, version 72, per-destination sharing

0 packets, 0 bytes

  via 192.168.100.1, 0 dependencies, recursive

    traffic share 1

    next hop 192.168.100.1, FastEthernet1/0/0 via 192.168.100.1/32

    valid adjacency

  via 192.168.101.1, 0 dependencies, recursive

    traffic share 1

    next hop 192.168.101.1, FastEthernet6/1 via 192.168.101.1/32

    valid adjacency

  0 packets, 0 bytes switched through the prefix

Step 4 show ip cef prefix detail

Use this command to show more detail for each of the active paths associated with a destination prefix. For example: 

Router# show ip cef 10.0.0.0 detail


10.0.0.0/8, version 72, per-destination sharing

0 packets, 0 bytes

  via 192.168.100.1, 0 dependencies, recursive

    traffic share 1

    next hop 192.168.100.1, FastEthernet1/0/0 via 192.168.100.1/32

    valid adjacency

  via 192.168.101.1, 0 dependencies, recursive

    traffic share 1

    next hop 192.168.101.1, FastEthernet6/1 via 192.168.101.1/32

    valid adjacency

  0 packets, 0 bytes switched through the prefix

Step 5 exit

Use this command to exit privileged EXEC mode. For example: 

Router# exit

Router>

Verifying the Adjacency or Next-Hop Information on the RP

To verify the adjacency or next-hop information, perform the following steps.

Adjacencies are added to the adjacency table when the adjacency is

•Indirectly configured manually

•Dynamically discovered through ARP

•Created when a routing protocol, for example, Border Gateway Protocol (BGP) or Open Shortest Path First (OSPF), forms a neighbor relationship

For more information on adjacencies, see the "Cisco Express Forwarding Overview" module.

SUMMARY STEPS

1. enable

2. show ip cef

3. show adjacency detail

4. show adjacency summary

5. show adjacency type number

6. show ip cef exact-route source-address destination-address

7. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. You can also enter this command in user EXEC mode. Enter your password if prompted. For example: 

Router> enable

Router#

Step 2 show ip cef

Use this command to find the output interface. For example: 

router# show ip cef


Prefix              Next Hop            Interface 

0.0.0.0/32          receive 

192.168.0.0/30      attached            Serial2/0/0:1 

192.168.0.0/32      receive

10.2.61.8/24        192.168.100.1       FastEthernet1/0/0

In this example, the output interface for the prefix 10.2.61.8/24 is FastEthernet 1/0/0, and the next hop address is 192.168.100.1.

Step 3 show adjacency detail

Use this command to display adjacency information, including Layer 2 information. For example: 

Router# show adjacency detail


Protocol Interface                 Address

IP       Ethernet1/0/0             10.2.61.8(7)

                                   0 packets, 0 bytes

                                   00107BC30D5C

                                   00500B32D8200800

                                   ARP        02:01:49

The encapsulation string 00107BC30D5C00500B32D8200800 is that of an adjacency used for traffic switched out of a router on an Ethernet link by means of Ethernet II encapsulation.

Step 4 show adjacency summary

Use this command to display Cisco Express Forwarding adjacency table summary information. For example: 

Router# show adjacency summary


Adjacency Table has 1 adjacency

  Interface                 Adjacency Count

  Ethernet1/0/0             1

Step 5 show adjacency type number

Use this command to display adjacency information for a particular interface. For example: 

Router# show adjacency fastethernet 2/3 


Protocol  Interface                  Address 

IP        FastEthernet2/3            172.20.52.1(3045)

IP        FastEthernet2/3            172.20.52.22(11)

Step 6 show ip cef exact-route source-address destination-address

Use this command to display the exact route for a source-destination IP address pair and verify the next-hop address. For example: 

Router# show ip cef exact-route 10.1.1.1 10.2.61.8


10.1.1.1         -> 10.2.61.8 :FastEthernet1/0/0 (next hop 192.168.100.1)

In this example, the exact route from source address 10.1.1.1 to destination address 10.2.61.8 is through interface Ethernet1/0/0 to next hop address 192.168.100.1.

Step 7 exit

Use this command to exit privileged EXEC mode. For example: 

Router# exit

Router>

Verifying Distributed Cisco Express Forwarding Operation on Your Router

Perform the following tasks, in the order presented, to verify distributed Cisco Express Forwarding operation on your router:

•Verifying That Distributed Cisco Express Forwarding Switching Is Enabled on the Input Interface on a Line Card

•Locating the Prefix in a Forwarding Table on a Line Card

•Finding the Distributed Cisco Express Forwarding Output Information Associated with the Prefix on a Line Card

•Verifying the Adjacency or Next-Hop Information on a Line Card

Syntax for Cisco Express Forwarding Commands on Line Cards

To perform tasks on router line cards, you need to use the following syntax: execute-on [slot slot-number | all] command. The execute-on commands apply only to the Cisco 12000 Series Internet routers and the Cisco 7500 series routers. The all keyword is available only on the Cisco 12000 Series Internet routers.

For example, use the following command to display FIB entries on the line cards in the first slot: 

Router# execute-on 0 show ip cef

To perform tasks on a Catalyst 6500 series switch, you use the following syntax: remote command module mod command. For example: 

Router# remote command module 2 show ip cef

The tasks in this document apply to the Cisco 7500 series and Cisco 12000 Series Internet routers.

Verifying That Distributed Cisco Express Forwarding Switching Is Enabled on the Input Interface on a Line Card

To verify that distributed Cisco Express Forwarding switching is enabled on the input (ingress) interface on the line card, perform the following steps.

SUMMARY STEPS

1. enable

2. show ip cef

3. execute-on slot slot-number show ip cef prefix

4. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. You can also enter this command in user EXEC mode. Enter your password if prompted. For example: 

Router> enable

Router#

Step 2 show ip cef

Use this command to verify that Cisco Express Forwarding is enabled globally. For example: 

Router# show ip cef


%CEF not running

If Cisco Express Forwarding is not running, use the ip cef command to enable (central) Cisco Express Forwarding or the ip cef distributed command to enable distributed Cisco Express Forwarding.

When Cisco Express Forwarding or distributed Cisco Express Forwarding is enabled, the show ip cef command shows a brief display of all FIB entries.

Step 3 execute-on slot slot-number show ip cef prefix

Use this command to verify information about interfaces on a line card. For example: 

Router# execute-on slot 0 show ip cef 192.68.0.0 255.255.255.0


show ip cef 192.68.0.0 255.255.255.0 from slot 0:


192.68.0.0/24, version 19, epoch 0, attached, connected

0 packets, 0 bytes

  via Ethernet5/0/0, 0 dependencies

    valid glean adjacency

Step 4 exit

Use this command to exit privileged EXEC mode. For example: 

Router# exit

Router>

Locating the Prefix in a Forwarding Table on a Line Card

To locate the prefix in a forwarding table on the line card, perform the following steps.

SUMMARY STEPS

1. enable

2. execute-on slot slot-number show ip cef

3. execute-on all show ip cef vrf vrf-name

4. Repeat Step 2 as many times as required to locate the prefix.

5. show ip cef

6. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. You can also enter this command in user EXEC mode. Enter your password if prompted. For example: 

Router> enable

Router#

Step 2 execute-on slot slot-number show ip cef

Use this command to show entries in the FIB on the line card and confirm that prefixes are listed in the FIB. For example: 

Router# execute-on slot 0 show ip cef 


show ip cef from slot 0:


Prefix              Next Hop             Interface

0.0.0.0/0            192.168.0.1          Ethernet5/0/0

0.0.0.0/32           receive

192.168.0.0/24       attached             Ethernet5/0/0

192.168.0.0/32       receive

192.168.0.1/32       192.168.0.1          Ethernet5/0/0

192.168.0.141/32     receive 

192.168.0.255/32     receive

239.224.0.0/4        drop

239.224.0.0/24       receive

255.255.255.255/32   receive

Step 3 execute-on all show ip cef vrf vrf-name

Use this command to locate prefixes in forwarding tables associated with Virtual Private Network (VPN) routing/forwarding instances (VRFs). For example, this command shows prefixes in the left-hand column for a VRF named vpn1: 

Router# execute-on all show ip cef vrf vpn1


Prefix              Next Hop            Interface

0.0.0.0/32          receive

10.1.0.0/8          10.0.0.1            Ethernet1/3

10.2.0.0/8          10.0.0.2            POS6/0

10.0.0.0/8          attached            Ethernet1/3

10.0.0.0/32         receive

10.0.0.1/32         10.0.0.1            Ethernet1/3

10.0.0.2/32         receive

10.255.255.255/32   receive

10.3.0.0/8          10.0.0.2            POS6/0

10.50.0.0/24        receive

255.255.255.255/32  receive

Step 4 Repeat Step 2 as many times as required to locate the prefix.

If distributed Cisco Express Forwarding is in a VPN, you might need to look at multiple VRFs.

Step 5 show ip cef

Use this command to show entries in the FIB on the RP and to verify that the FIB on the line card is synchronized with the FIB maintained by the router. For example: 

Router# show ip cef 


Prefix              Next Hop            Interface

[...]

10.2.61.8/24        192.168.100.1       FastEthernet1/0/0

                    192.168.101.1       FastEthernet6/1

[...]

Compare the prefixes, next hops, and interfaces in this output with those in the output from Step 1 to verify that FIB on the line card is synchronized with the FIB maintained by the router.

Step 6 exit

Use this command to exit privileged EXEC mode. For example: 

Router# exit

Router>

Finding the Distributed Cisco Express Forwarding Output Information Associated with the Prefix on a Line Card

To find the distributed Cisco Express Forwarding output information associated with the prefix on a line card, perform the following steps.

SUMMARY STEPS

1. enable

2. execute-on slot slot-number show ip cef

3. execute-on slot slot-number show ip cef prefix

4. execute-on slot slot-number show ip cef prefix detail

5. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. You can also enter this command in user EXEC mode. Enter your password if prompted. For example: 

Router> enable

Router#

Step 2 execute-on slot slot-number show ip cef

Use this command to confirm that the prefix is listed in the FIB. For example: 

Router# execute-on slot 0 show ip cef


show ip cef from slot 0:


Prefix              Next Hop             Interface

0.0.0.0/0           192.168.0.1           Ethernet5/0/0

0.0.0.0/32          receive

192.168.0.0/24      attached              Ethernet5/0/0

192.168.0.0/32      receive

192.168.0.1/32      192.168.0.1           Ethernet5/0/0

192.168.0.141/32    receive

192.168.0.255/32    receive

239.224.0.0/4       drop

239.224.0.0/24      receive

255.255.255.255/32  receive

Step 3 execute-on slot slot-number show ip cef prefix

Use this command to display the prefix entry in the FIB on a line card. For example: 

Router# execute-on slot 3 show ip cef 192.68.0.0 255.255.255.0


show ip cef 192.168.0.0 255.255.255.0 from slot 0:


192.168.0.0/24, version 19, epoch 0, attached, connected

0 packets, 0 bytes

  via Ethernet5/0/0, 0 dependencies

    valid glean adjacency

Step 4 execute-on slot slot-number show ip cef prefix detail

Use this command to show more detail for each of the active paths associated with a destination prefix on a line card. For example: 

Router# execute-on slot 0 show ip cef 10.24.48.32 detail


show ip cef 192.168.0.0 255.255.255.0 from slot 0:


192.168.0.0/24, version 19, epoch 0, attached, connected

0 packets, 0 bytes

  via Ethernet5/0/0, 0 dependencies

    valid glean adjacency

Step 5 exit

Use this command to exit privileged EXEC mode. For example: 

Router# exit

Router>

Verifying the Adjacency or Next-Hop Information on a Line Card

To verify the adjacency or next-hop information on a line card, perform the following steps.

Cisco Express Forwarding adds an adjacency to the adjacency table when the adjacency is

•Indirectly configured manually

•Dynamically discovered through ARP

•Created when a routing protocol, for example, BGP or OSPF, forms a neighbor relationship

For more information on adjacencies, see the Cisco Express Forwarding Overview module.

SUMMARY STEPS

1. enable

2. show ip cef

3. show adjacency detail

4. show adjacency summary

5. show adjacency type number

6. show ip cef exact-route source-address destination-address

7. execute-on all show ip cef destination

8. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. You can also enter this command in user EXEC mode. Enter your password if prompted. For example: 

Router> enable

Router#

Step 2 show ip cef

Use this command to determine the output interface. For example: 

router# show ip cef


Prefix              Next Hop            Interface 

0.0.0.0/32          receive 

192.168.0.0/30      attached            Serial2/0/0:1 

192.168.0.0/32      receive

10.2.61.8/24        192.168.100.1       FastEthernet1/0/0

In this example, the output interface for the prefix 10.2.61.8/24 is FastEthernet 1/0/0, and the next hop address is 192.168.100.1.

Step 3 show adjacency detail

Use this command to display adjacency information, including Layer 2 information. For example: 

Router# show adjacency detail


Protocol Interface                 Address

IP       Ethernet1/0/0             10.2.61.8(7)

                                   0 packets, 0 bytes

                                   00107BC30D5C

                                   00500B32D8200800

                                   ARP        02:01:49

The encapsulation string 00107BC30D5C00500B32D8200800 is that of an adjacency used for traffic switched out of a router on an Ethernet link by means of Ethernet II encapsulation. (The first 12 characters are the MAC address of the destination next-hop interface. The next 12 characters represent the MAC address of the source interface of the packet. The last 4 characters [0x0800] represent the Ethernet II encapsulation value for IP.)

Step 4 show adjacency summary

Use this command to display Cisco Express Forwarding adjacency table summary information. For example: 

Router# show adjacency summary


Adjacency Table has 1 adjacency

  Interface                 Adjacency Count

  Ethernet1/0/0             1

Step 5 show adjacency type number

Use this command to display adjacency information for a particular interface. For example: 

Router# show adjacency fastethernet 2/3 


Protocol  Interface                  Address 

IP        FastEthernet2/3            172.20.52.1(3045)

IP        FastEthernet2/3            172.20.52.22(11)

Step 6 show ip cef exact-route source-address destination-address

Use this command to display the exact route for a source-destination IP address pair and verify the next-hop address. For example: 

Router# show ip cef exact-route 10.1.1.1 10.2.61.8


10.1.1.1         -> 10.2.61.8 :FastEthernet1/0/0 (next hop 192.168.100.1)

In this example, the exact route from source address 10.1.1.1 to destination address 10.2.61.8 is through interface Ethernet1/0/0 to next hop address 192.168.100.1.

Step 7 execute-on all show ip cef destination

Use this command to display output interfaces and next hops for all line cards. For example: 

Router# execute-on all show ip cef 10.20.84.32


========= Line Card (Slot 1) =======

10.16.0.0/13, version 408935, cached adjacency 0.0.0.0

0 packets, 0 bytes

Flow: AS 6172, mask 13

via 172.16.213.1, 0 dependencies, recursive

next hop 172.16.213.1, POS1/0.500 via 172.16.213.0/30

valid cached adjacency


========= Line Card (Slot 2) =======

10.16.0.0/13, version 13719, cached adjacency 0.0.0.0

0 packets, 0 bytes

Flow: AS 6172, mask 13

via 172.16.213.1, 0 dependencies, recursive

next hop 172.16.213.1, POS1/0.500 via 172.16.213.0/30

valid cached adjacency

Step 8 exit

Use this command to exit privileged EXEC mode. For example: 

Router# exit

Router>

Interpreting Information in Cisco Express Forwarding Command Output

Perform the following tasks to interpret information in Cisco Express Forwarding command output:

•Verifying That the Cisco Express Forwarding Information Looks As Expected (optional)

•Interpreting MPLS Information in Cisco Express Forwarding Output (optional)

Verifying That the Cisco Express Forwarding Information Looks As Expected

Perform the following tasks to verify that the Cisco Express Forwarding information looks as you expected.

SUMMARY STEPS

1. enable

2. show ip route

3. show ip cef

4. Compare the command output in Steps 2 and 4.

5. execute-on slot slot-number show ip cef

6. Compare the command output in Steps 2 and 4.

7. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. You can also enter this command in user EXEC mode. Enter your password if prompted. For example: 

Router> enable

Router#

Step 2 show ip route

Use this command to look at the forwarding information contained in the IP routing table. For example: 

Router# show ip route

...


     10.1.0.0/32 is subnetted, 1 subnets

O       10.1.2.3 [110/3] via 10.5.5.5, 00:00:03, POS2/0/0

     10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks

C       10.5.5.5/32 is directly connected, POS2/0/0

C       10.5.5.0/24 is directly connected, POS2/0/0

     10.7.0.0/24 is subnetted, 1 subnets

O       10.7.8.0 [110/3] via 10.5.5.5, 00:00:04, POS2/0/0

     10.0.0.0/24 is subnetted, 2 subnets

O       10.23.64.0 [110/12] via 10.5.5.5, 00:00:04, POS2/0/0

O       10.23.66.0 [110/12] via 10.5.5.5, 00:00:04, POS2/0/0

     10.47.0.0/32 is subnetted, 1 subnets

O       10.47.0.10 [110/3] via 10.5.5.5, 00:00:04, POS2/0/0

O    172.16.57.0/24 [110/3] via 10.5.5.5, 00:00:04, POS2/0/0

     10.150.0.0/24 is subnetted, 1 subnets

C       10.150.3.0 is directly connected, Fddi0/0/0

O    192.168.92.0/24 [110/2] via 10.5.5.5, 00:00:04, POS2/0/0

In the example, c indicates a directly connected route and o represents a route discovered by means of OSPF.

Step 3 show ip cef

Use this command to display entries in the FIB. For example: 

Router# show ip cef


Prefix              Next Hop            Interface

0.0.0.0/0           10.5.5.5             POS2/0/0	(default route)

0.0.0.0/32          receive

10.1.2.3/32         10.5.5.5             POS2/0/0	(two paths)

                    10.150.3.9           Fddi0/0/0

10.5.5.0/24         attached             POS2/0/0

10.5.5.0/32         receive

10.5.5.5/32         attached             POS2/0/0	(glean adjacency)

10.5.5.6/32         receive				(our interface)

10.5.5.255/32       receive				(broadcast)

10.7.8.0/24         10.5.5.5             POS2/0/0

                    10.150.3.9           Fddi0/0/0

10.23.64.0/24       10.150.3.9           Fddi0/0/0

10.23.66.0/24       10.150.3.9           Fddi0/0/0	(normal route)

10.47.0.10/32       10.150.3.9           Fddi0/0/0

10.150.3.0/24       attached             Fddi0/0/0

10.150.3.0/32       receive

10.150.3.1/32       receive

10.150.3.255/32     receive

192.168.92.0/24     10.5.5.5             POS2/0/0

                    10.150.3.9           Fddi0/0/0

172.16.57.0/24      10.5.5.5             POS2/0/0

                    10.150.3.9           Fddi0/0/0

239.224.0.0/4       receive				(multicast)

255.255.255.255/32  receive				(all 1s broadcast)

Step 4 Compare the command output in Steps 2 and 3.

Cisco Express Forwarding maintains the information contained in the IP routing table structured in a way that optimizes forwarding. Check that there is a one-to-one correlation between FIB entries and routing table entries. For example, the following lines from the sample output in Step 2 and Step 3 show a one-to-one correlation. The destination prefix 192.92.92.0/24, the next hop IP address 10.5.5.5, and the next-hop interface POS2/0/0 are the same.

•From the show ip route command output in Step 2: 

192.168.92.0/24 [110/2] via 10.5.5.5, 00:00:04, POS2/0/0

•From the show ip cef command output in Step 3: 

192.168.92.0/24      10.5.5.5             POS2/0/0

If there is not a one-to-one correlation, you can recreate the central FIB table by clearing the IP routing table and allowing the routing table to be rebuilt, which in turn causes the central FIB table to be repopulated with up-to-date routing information.

Step 5 (For distributed Cisco Express Forwarding operation only) execute-on slot slot-number show ip cef

Use this command to display FIB entries on all line cards. For example: 

Router# execute-on slot 2 show ip cef


show ip cef from slot 2: 


Prefix              Next Hop            Interface

0.0.0.0/0           10.5.5.5             POS2/0/0

0.0.0.0/32          receive

10.1.2.3/32         10.5.5.5             POS2/0/0

                    10.150.3.9           Fddi0/0/0

105.5.5.0/24        attached             POS2/0/0

10.5.5.0/32         receive

10.5.5.5/32         attached             POS2/0/0

10.5.5.6/32         receive

10.5.5.255/32       receive

10.7.8.0/24         10.5.5.5             POS2/0/0

                    10.150.3.9           Fddi0/0/0

10.7.54.0/24        attached             Fddi0/1/0

10,7.54.0/32        receive

10.7.54.3/32        receive

10.7.54.255/32      receive

10.23.64.0/24       10.150.3.9           Fddi0/0/0

10.23.66.0/24       10.150.3.9           Fddi0/0/0

10.47.0.10/32       10.150.3.9           Fddi0/0/0

10.150.3.0/24       attached             Fddi0/0/0

10.150.3.0/32       receive

10.150.3.1/32       receive

10.150.3.255/32     receive

192.168.92.0/24     10.5.5.5             POS2/0/0

                    10.150.3.9           Fddi0/0/0

172.16.57.0/24      10.5.5.5             POS2/0/0

                    10.150.3.9           Fddi0/0/0

239.224.0.0/4       receive

255.255.255.255/32  receive

Step 6 (For distributed Cisco Express Forwarding operation only) Compare the command output in Steps 3 and 5.

The output from the show ip cef command in Step 3 should be identical to the output from the execute-on slot 2 show ip cef command in Step 5. If the outputs are not identical, see the Configuring Cisco Express Forwarding Consistency Checkers for Route Processors and Line Cards module for information on synchronizing FIB entries on the RP and the line card.

Step 7 exit

Use this command to exit privileged EXEC mode. For example: 

Router# exit

Router>

Interpreting MPLS Information in Cisco Express Forwarding Output

Perform the following steps to interpret Multiprotocol Label Switching (MPLS) information in Cisco Express Forwarding output.

Cisco Express Forwarding and MPLS Interaction

Cisco Express Forwarding interacts with a label switched path (LSP) primarily at the beginning and end of the LSP—that is, on label imposition (IP packet to MPLS packet) and label disposition (MPLS packet to IP packet). Output from Cisco Express Forwarding commands should show these processes.

The Cisco implementation of MPLS leverages the advantages of Cisco Express Forwarding. When you use a router as an MPLS edge router, Cisco Express Forwarding identifies the route for incoming packets and finds the label to apply to the packet.

However, when you use a router as a label switch router (LSR), tables from the MPLS label forwarding information base (LFIB) are used to switch MPLS packets. These tables are distributed to the Versatile Interface Processor (VIP) or to line cards in the same way that the FIB tables are distributed in Cisco Express Forwarding.

MPLS VPNs and Cisco Express Forwarding Tables

A customer-site VRF contains all the routes available to the site from the VPNs to which it belongs. VPN routing information is stored in the IP routing table and in the Cisco Express Forwarding table for each VRF. A separate set of tables is maintained for each VRF, which prevents information from being forwarded outside a VPN and prevents packets that are outside a VPN from being forwarded to a router within the VPN. Based on the routing information stored in the VRF IP routing table and the VRF Cisco Express Forwarding table, packets are forwarded to their destinations. Output from Cisco Express  Forwarding commands shows details from the VRF Cisco Express Forwarding tables.

SUMMARY STEPS

1. enable

2. show ip cef vrf vrf-name detail

3. exit

DETAILED STEPS

Step 1 enable

Use this command to enable privileged EXEC mode. You can also enter this command in user EXEC mode. Enter your password if prompted. For example: 

Router> enable

Router#

Step 2 show ip cef vrf vrf-name detail

Use this command to display detailed information from the Cisco Express Forwarding forwarding table that is associated with a VRF. For example: 

Router# show ip cef vrf vpn1 detail 


IP CEF with switching (Table Version 10), flags=0x0

  8 routes, 0 reresolve, 0 unresolved (0 old, 0 new)

  46 leaves, 51 nodes, 54640 bytes, 361 inserts, 315 invalidations

  0 load sharing elements, 0 bytes, 0 references

  universal per-destination load sharing algorithm, id F968AD29

  5 CEF resets, 38 revisions of existing leaves

  refcounts:  1400 leaf, 1392 node


Adjacency Table has 2 adjacencies

0.0.0.0/32, version 0, receive

192.168.6.0/24, version 9, cached adjacency to Serial0/1.1

0 packets, 0 bytes

The following section of the Cisco Express Forwarding output provides MPLS information for the first adjacency. The "tag rewrite" is an equivalent of a Cisco Express Forwarding adjacency. Look at the tags imposed field. The first tag {20} is the tag used to reach the next hop, 10.1.1.13. The second tag {30} is the tag advertised to the local provider edge (PE) router by the remote PE router. 

  tag information set 

    local tag: VPN-route-head

    fast tag rewrite with Se0/1.1, point2point, tags imposed: {20 30}

  via 10.10.10.6, 0 dependencies, recursive

    next hop 10.1.1.13, Serial0/1.1 via 10.10.10.6

    valid cached adjacency

    tag rewrite with Se0/1.1, point2point, tags imposed: {20 30}

The following section of the output provides information about the second adjacency. For the second adjacency, no tag rewrite occurs as indicated by the entry "tag rewrite with , ," and MPLS tags are not imposed on the packet indicated by the entry "tags imposed : {}." The router also discards this packet indicated by the entry "valid discard adjacency." 

192.168.4.0/24, version 6, attached, connected

0 packets, 0 bytes

  tag information set

    local tag: 28

  via Loopback102, 0 dependencies

    valid discard adjacency

    tag rewrite with , , tags imposed: {}

192.168.4.0/32, version 4, receive

192.168.4.1/32, version 3, receive

192.168.4.255/32, version 5, receive

192.168.0.0/24, version 2, receive

255.255.255.255/32, version 1, receive

Step 3 exit

Use this command to exit to user EXEC mode. For example: 

Router# exit

Router>

Configuration Examples for Basic Cisco Express Forwarding

There are no configuration examples for Cisco Express Forwarding. Cisco Express Forwarding is enabled by default.

Where to Go Next

If you want to disable Cisco Express Forwarding or distributed Cisco Express Forwarding operation, refer to Enabling or Disabling Cisco Express Forwarding or distributed Cisco Express Forwarding to Customize Switching/Forwarding for Dynamic Networks.

Additional References

Related Documents

Related Topic
Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

IP switching commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples.

Cisco IOS IP Switching Command Reference

List of the features documented in the Cisco Express Forwarding modules

Cisco Express Forwarding Features Roadmap

Overview of the Cisco Express Forwarding feature

Cisco Express Forwarding Overview

Tasks for enabling or disabling Cisco Express Forwarding or distributed Cisco Express Forwarding

Enabling or Disabling Cisco Express Forwarding or distributed Cisco Express Forwarding to Customize Switching/Forwarding for Dynamic Networks

Tasks for configuring a load-balancing scheme for Cisco Express Forwarding

Configuring a Load-Balancing Scheme for Cisco Express Forwarding Traffic

Tasks for configuring Cisco Express Forwarding consistency checkers

Configuring Cisco Express Forwarding Consistency Checkers for Route Processors and Line Cards

Tasks for configuring epochs for Cisco Express Forwarding tables

Configuring Epochs to Clear and Rebuild Cisco Express Forwarding and Adjacency Tables

Tasks for configuring and verifying Cisco Express Forwarding network accounting

Configuring Cisco Express Forwarding Network Accounting

Tasks for customizing the display of recorded Cisco Express Forwarding events

Customizing the Display of Recorded Cisco Express Forwarding Events

Verification steps for Cisco Express Forwarding switching

How to Verify Cisco Express Forwarding Switching

Troubleshooting tips for incomplete adjacencies

Troubleshooting Incomplete Adjacencies with CEF

Description and use of the Cisco Express Forwarding consistency checkers available for the Cisco 7500 and 12000 series routers

Troubleshooting Prefix Inconsistencies with Cisco Express Forwarding

Information about troubleshooting Cisco Express Forwarding routing loops and suboptimal routing

Troubleshooting Cisco Express Forwarding Routing Loops

Causes of common Cisco Express Forwarding-related error messages on platforms running distributed Cisco Express Forwarding switching (Cisco 7500 series routers and Cisco 12000 Series Internet routers) and how to troubleshoot them

Troubleshooting Cisco Express Forwarding-Related Error Messages

Explanation of and troubleshooting information for the Cisco IOS software implementation of Layer 3 load balancing across multiple parallel links when Cisco Express Forwarding is used

Troubleshooting Load Balancing Over Parallel Links Using Cisco Express Forwarding

QoS features that require Cisco Express Forwarding

When Is CEF Required for Quality of Service


Standards

Standard
Title

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

—


MIBs

MIB
MIBs Link

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

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFC
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 Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html


Feature Information for Configuring Basic Cisco Express Forwarding

Table 1 lists the release history for this feature.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 1 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.

Table 1 Feature Information for Configuring Basic Cisco Express Forwarding 

Feature Name
Releases
Feature Configuration Information

CEF/dCEF - Cisco Express Forwarding

Cisco IOS XE Release 2.1
15.0(1)S

This feature was introduced on Cisco ASR 1000 Series Routers.

This feature was integrated into Cisco IOS Release 15.0(1)S.


Glossary

adjacency—A relationship formed between selected neighboring routers and end nodes for the purpose of exchanging routing information. Adjacency is based upon the use of a common media segment by the routers and nodes involved.

Cisco Express Forwarding—A Layer 3 switching technology. Cisco Express Forwarding can also refer to central Cisco Express Forwarding mode, one of two modes of Cisco Express Forwarding operation. Cisco Express Forwarding enables a Route Processor (RP) to perform express forwarding. Distributed Cisco Express Forwarding is the other mode of Cisco Express Forwarding operation.

distributed Cisco Express Forwarding—A type of Cisco Express Forwarding switching in which line cards (such as Versatile Interface Processor (VIP) line cards) maintain identical copies of the forwarding information base (FIB) and adjacency tables. The line cards perform the express forwarding between port adapters; this relieves the Route Switch Processor of involvement in the switching operation.

FIB—forwarding information base. A component of Cisco Express Forwarding. The router uses the FIB lookup table to make destination-based switching decisions during Cisco Express Forwarding operation. The router maintains a mirror image of the forwarding information in an IP routing table.

IPC—interprocess communication. The mechanism that enables the distribution of Cisco Express Forwarding tables from the Route Switch Processor (RSP) to the line card when the router is operating in distributed Cisco Express Forwarding mode.

label disposition—The removal of Multiprotocol Label Switching (MPLS) headers at the edge of a network. In MPLS label disposition, packets arrive on a router as MPLS packets and, with the headers removed, are transmitted as IP packets.

label imposition—The action of putting a label on a packet.

LER—label edge router. A router that performs label imposition.

LFIB—label forwarding information base. The data structure used by switching functions to switch labeled packets.

LIB—label information base. A database used by a label switch router (LSR) to store labels learned from other LSRs, as well as labels assigned by the local LSR.

line card—A general term for an interface processor that can be used in various Cisco products. For example, a Versatile Interface Processor (VIP) is a line card for the Cisco 7500 series router.

LSP—label switched path. A sequence of hops (Router 0...Router n). A packet travels from R0 to Rn by means of label switching mechanisms. An LSP can be chosen dynamically, based on normal routing mechanisms, or it can be configured manually.

LSR—label switch router. A Layer 3 router that forwards a packet based on the value of a label encapsulated in the packet.

MPLS—Multiprotocol Label Switching. An emerging industry standard for the forwarding of packets along the normal routing paths (sometimes called MPLS hop-by-hop forwarding).

prefix—The network address portion of an IP address. A prefix is specified by a network and mask and is generally represented in the format network/mask. The mask indicates which bits are the network bits. For example, 1.0.0.0/16 means that the first 16 bits of the IP address are masked, making them the network bits. The remaining bits are the host bits. In this example, the network number is 10.0.

RIB—Routing Information Base. A central repository of routes that contains Layer 3 reachability information and destination IP addresses or prefixes. The RIB is also known as the routing table.

RP—Route Processor. The processor module in the Cisco 7000 series routers that contains the CPU, system software, and most of the memory components that are used in the router. It is sometimes called a supervisory processor.

RSP—Route Switch Processor. The processor module used in the Cisco 7500 series routers that integrates the functions of the Route Processor (RP) and the Switch Processor (SP).

SP—Switch Processor. Cisco 7000 series processor module that acts as the administrator for all CxBus activities. It is also sometimes called a CiscoBus controller.

VIP—Versatile Interface Processor. An interface card used in Cisco 7000 and Cisco 7500 series routers. The VIP provides multilayer switching and runs Cisco IOS.

VPN—Virtual Private Network. The result of a router configuration that enables IP traffic to use tunneling to travel securely over a public TCP/IP network.

VRF—A Virtual Private Network (VPN) routing/forwarding instance. A VRF consists of an IP routing table, a derived forwarding table, a set of interfaces that use the forwarding table, and a set of rules and routing protocols that determine what goes into the forwarding table. In general, a VRF includes the routing information that defines a customer VPN site that is attached to a PE router.

Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2005—2010 Cisco Systems, Inc. All rights reserved.