Table Of Contents
Cisco Express Forwarding Commands
clear ip cef prefix-statistics
Cisco Express Forwarding Commands
This chapter documents commands used to configure Cisco Express Forwarding in Cisco IOS software. For guidelines on configuring Cisco Express Forwarding, refer to the Cisco IOS Switching Services Configuration Guide.
Note
Beginning with Cisco IOS Release 11.3, all commands supported on the Cisco 7500 series routers are also supported on Cisco 7000 series routers.
clear adjacency
To clear the Cisco Express Forwarding (CEF) adjacency table, use the clear adjacency EXEC command.
clear adjacency
Syntax Description
This command has no arguments or keywords.
Command Modes
EXEC
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Usage Guidelines
When you issue this command, entries in the adjacency table that resides on the route processor are removed and then repopulated. During repopulation, Layer 2 next hop information is reevaluated.
With Distributed CEF (dCEF) mode, the adjacency tables that reside on line cards are always synchronized to the adjacency table that resides on the route processor. Therefore, clearing the adjacency table on the route processor using the clear adjacency command also clears the adjacency tables on the line cards; all changes are propagated to the line cards.
Examples
The following example clears the adjacency table:
clear adjacencyRelated Commands
clear cef linecard
To clear Cisco Express Forwarding (CEF) information from line cards, use the clear cef linecard EXEC command.
clear cef linecard [slot-number] [adjacency | interface | prefix]
Syntax Description
Command Modes
EXEC
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Usage Guidelines
This command is available only on routers with line cards. This command clears CEF information only on the line cards; CEF information on the route processor is not affected.
Once you clear CEF information from line cards, the corresponding information from the route processor is propagated to the line cards. Inter Process Communication (IPC) ensures that CEF information on the route processor matches the CEF information on the line cards.
Examples
The following example clears the CEF information from the line cards:
clear cef linecardRelated Commands
clear ip cef prefix-statistics
To clear Cisco Express Forwarding (CEF) counters by resetting the packet and byte count to zero (0), use the clear ip cef prefix-statistics EXEC command.
clear ip cef {network [mask] | *} prefix-statistics
Syntax Description
network
Clears counters for a FIB entry specified by network.
mask
(Optional) Clears counters for a FIB entry specified by network and mask.
*
Clears counters for all FIB entries.
Command Modes
EXEC
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Examples
The following example resets the CEF packet and byte count to zero:
clear ip cef prefix-statisticsRelated Commands
show adjacency
Displays CEF adjacency table information.
show ip cef
Displays entries in the FIB that are unresolved or displays a FIB summary.
ip cef
To enable Cisco Express Forwarding (CEF) on the route processor card, use the ip cef global configuration command. To disable CEF, use the no form of this command.
ip cef [distributed]
no ip cef [distributed]
Syntax Description
distributed
(Optional) Enables distributed CEF (dCEF) operation. Distributes CEF information to line cards. Line cards perform express forwarding.
Defaults
Command Modes
Global configuration
Command History
Usage Guidelines
This command is not available on the Cisco 12000 series GSR because that router series operates only in distributed CEF mode.
CEF is advanced Layer 3 IP switching technology. CEF optimizes network performance and scalability for networks with dynamic, topologically dispersed traffic patterns, such as those associated with Web-based applications and interactive sessions.
Examples
The following example enables standard CEF operation:
ip cefThe following example enables dCEF operation:
ip cef distributedRelated Commands
ip cef accounting
To enable network accounting of Cisco Express Forwarding (CEF), use the ip cef accounting global configuration command. To disable network accounting of CEF, use the no form of this command.
ip cef accounting [per-prefix] [non-recursive]
no ip cef accounting [per-prefix] [non-recursive]
Syntax Description
Defaults
Accounting is disabled by default.
Command Modes
Global configuration
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Usage Guidelines
You might want to collect statistics to better understand CEF patterns in your network.
When you enable network accounting for CEF from global configuration mode, accounting information is collected at the route processor when CEF mode is enabled and at the line cards when dCEF mode is enabled.
You can then view the collected accounting information using the show ip cef command.
Note
Examples
The following example enables the collection of CEF accounting information:
ip cef accountingRelated Commands
show ip cef
Displays entries in the FIB that are unresolved or displays a FIB summary.
ip cef traffic-statistics
To change the time intervals used to control the collection of Cisco Express Forwarding (CEF) traffic load statistics, use the ip cef traffic-statistics global configuration command. To restore the default values, use the no form of this command.
ip cef traffic-statistics [load-interval seconds] [update-rate seconds]
no ip cef traffic-statistics
Syntax Description
Defaults
load-interval: 30 seconds
update-rate: 10 seconds
Command Modes
Global configuration
Command History
Usage Guidelines
This command configures the CEF traffic load statistics that are used to determine the behavior of the Next Hop Resolution Protocol (NHRP) — a protocol used by routers to dynamically discover the MAC address of other routers and hosts connected to a nonbroadcast multiaccess (NBMA) network.
The ip nhrp trigger-svc command sets the threshold by which NHRP sets up and tears down a connection. The threshold is the CEF traffic load statistics. To change the interval over which that threshold is determined, use the load-interval seconds keyword and argument of the ip cef traffic-statistics command.
Examples
In the following example, the triggering and teardown thresholds are calculated based on an average over 120 seconds:
ip cef traffic-statistics load-interval 120Related Commands
ip nhrp trigger-svc
Configures when NHRP will set up and tear down an SVC based on aggregate traffic rates.
ip load-sharing
To enable load balancing for Cisco Express Forwarding (CEF), use the ip load-sharing interface configuration command. To disable load balancing for CEF, use the no form of this command.
ip load-sharing [per-packet] [per-destination]
no ip cef [per-packet]
Syntax Description
per-packet
(Optional) Enables per-packet load balancing on the interface.
per-destination
(Optional) Enables per-destination load balancing on the interface.
Defaults
Per-destination load balancing is enabled by default when you enable CEF.
Command Modes
Interface configuration
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Usage Guidelines
Per-packet load balancing allows the router to send data packets over successive equal-cost paths without regard to individual destination hosts or user sessions. Path utilization is good, but packets destined for a given destination host might take different paths and might arrive out of order.
Note
Per-destination load balancing allows the router to use multiple, equal-cost paths to achieve load sharing. Packets for a given source-destination host pair are guaranteed to take the same path, even if multiple, equal-cost paths are available. Traffic for different source-destination host pairs tend to take different paths.
Note
Examples
The following example enables per-packet load balancing:
interface E0ip load-sharing per-packetThe following example enables per-destination load balancing:
interface E0ip load-sharing per-destinationRelated Commands
interface
Configures an interface type and enters interface configuration mode.
ip cef
Enables CEF on the route processor card.
ip route-cache cef
To enable Cisco Express Forwarding (CEF) operation on an interface after CEF operation has been disabled, use the ip route-cache cef interface configuration command. To disable CEF operation on an interface, use the no form of this command.
ip route-cache cef
no ip route-cache cef
Syntax Description
This command has no arguments or keywords.
Defaults
When standard CEF or dCEF operation is enabled globally, all interfaces that support CEF are enabled by default.
Command Modes
Interface configuration
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Usage Guidelines
CEF is advanced Layer 3 switching technology for IP. CEF optimizes network performance and scalability for networks with dynamic, topologically dispersed traffic patterns, such as those associated with Web-based applications and interactive type sessions.
Because all interfaces that support CEF or dCEF are enabled by default when you enable standard CEF or dCEF operation globally, you use the no form of the command to turn off CEF operation on a particular interface.
You might want to disable CEF or dCEF on a particular interface because that interface is configured with a feature that CEF or dCEF does not support. For example, policy routing and CEF cannot be used together. You might want one interface to support policy routing while the other interfaces support CEF. In this case, you would turn on CEF globally, but turn off CEF on the interface configured for policy routing, enabling all but one interface to express forward.
When you disable CEF or dCEF, Cisco IOS software switches packets using the next fastest switching path. In the case of dCEF, the next fastest switching path is CEF on the route processor.
If you have disabled CEF or dCEF operation on an interface and want to reenable it, you can do so by using the ip route-cache cef command in interface configuration mode.
Note
Examples
The following example enables CEF operation on the router (globally), but turns off CEF operation on Ethernet interface 0:
ip cefinterface e0no ip route-cache cefThe following example enables dCEF operation on the router (globally), but turns off CEF operation on Ethernet interface 0:
ip cef distributedinterface e0no ip route-cache cefThe following example reenables dCEF operation on Ethernet interface 0:
ip cef distributedinterface e0ip route-cache cefRelated Commands
interface
Configures an interface type and enters interface configuration mode.
ip cef
Enables CEF on the route processor card.
show adjacency
To display Cisco Express Forwarding (CEF) adjacency table information, use the show adjacency EXEC command.
show adjacency [detail]
Syntax Description
Command Modes
EXEC
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Usage Guidelines
This command is available only on routers that have RP cards.
Examples
The following is sample output from the show adjacency detail command.
Router# show adjacency detailProtocol Interface AddressIP Ethernet1/0/0 9.2.61.1(7)0 packets, 0 bytes00107BC30D5C00500B32D8200800ARP 02:01:49The encapsulation string 00107BC30D5C00500B32D8200800 is that of an adjacency used for traffic switched out of a router on an Ethernet link using Ethernet II encapsulation.
Table 97 describes the significant fields shown in the display.
Related Commands
show cef
To display which packets the line cards dropped or to display which packets were not express forwarded, use the show cef EXEC command.
show cef [drop | not-cef-switched]
Syntax Description
drop
(Optional) Displays which packets were dropped by each line card.
not-cef-switched
(Optional) Displays which packets were sent to a different switching path.
Command Modes
EXEC
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Usage Guidelines
This command is available only on routers that have RP cards.
A line card might drop packets due to encapsulation failure, no route information, or no adjacency information.
A packet is sent to a different switching path because Cisco Express Forwarding (CEF) does not support the encapsulation or feature, the packet is destined for the router, or the packet has IP options, such as time stamp and record route. IP options are process switched.
Examples
The following is sample output from the show cef drop command:
Router# show cef dropCEF Drop StatisticsSlot Encap_fail Unresolved Unsupported No_route No_adj ChksumErrRP 4 89 0 4 0 01 0 0 0 0 0 02 0 0 5 0 0 5Table 98 describes the fields shown in the output.
The following is sample output from the show cef not-cef-switched command:
Router# show cef not-cef-switchedCEF Packets passed on to next switching layerSlot No_adj No_encap Unsupp'ted Redirect Receive Options Access FragRP 0 0 0 0 91584 0 0 01 0 0 0 0 0 0 0 02 0 0 0 0 0 0 0 0Table 99 describes the fields shown in the output.
Related Commands
show cef interface
Displays CEF-related interface information.
show cef linecard
Displays CEF-related interface information by line card.
show cef interface
To display Cisco Express Forwarding (CEF) related interface information, use the show cef interface EXEC command.
show cef interface type number [detail]
Syntax Description
type number
Interface type and number about which to display CEF-related information.
detail
(Optional) Displays detailed CEF information for the specified interface type and number.
Command Modes
EXEC
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Usage Guidelines
This command is available on routers that have RP cards and line cards.
The detail command displays more CEF-related information for the specified interface.
You can use this command to show the CEF state on an individual interface.
Examples
The following is sample output from the show cef interface detail command for Ethernet interface 0:
Router# show cef interface E0 detailEthernet1/0/0 is up (if_number 6)Internet address is 172.19.177.20/24ICMP redirects are always sentPer-packet load balancing is disabledInbound access list is 10Outbound access list is not setHardware idb is Ethernet1/0/0Fast switching type 1, interface type 5IP Distributed CEF switching enabledIP Feature CEF switching turbo vectorFast flags 0x4. ifindex 5(5)Slot 1 Slot unit 0 VC -1Hardware transmit queue ptr 0x48001A00 (0x48001A00) >- debugging purposes Transmit limit accumulator 0x48001A02 (0x48001A02) IP MTU 1500Table 100 describes the fields shown in the output.
Related Commands
show cef linecard
To display Cisco Express Forwarding (CEF) related interface information by line card, use the show cef linecard EXEC command.
show cef linecard [slot-number] [detail]
Syntax Description
Command Modes
EXEC
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Usage Guidelines
This command is available only on routers that have RP cards.
When you omit the slot-number argument, information about all line cards is displayed. When you omit the slot-number argument and include the detail keyword, detailed information is displayed for all linecards. When you omit all keywords and arguments, the show cef linecard command displays important information about all line cards in table format.
Examples
The following is sample output from the show cef linecard command. The command displays information for the line cards.
Router# show cef linecardCEF table version 115705, 45877 routesSlot CEF-ver MsgSent XdrSent Seq MaxSeq LowQ HighQ Flags1 238 668 9641 616 616 0 0 up, sync2 238 683 10782 619 629 0 0 up, syncTable 101 describes the fields shown in the output.
The following is sample output from the show cef linecard detail command for the line card in slot number 2:
Router# show cef linecard 2 detailCEF line card slot number 2, status up, sync, disabledline card CEF version number 238Sequence number 616, Maximum sequence number expected 616Send failed 0, Out Of Sequence 0line card CEF reset 2, reloaded 292299/15/91 prefix/adjacency/interface elements queued49641 elements packed in 668 messages(1341286 bytes) sent0/0 xdr elements in LowQ/HighQInput packets 0, bytes 0 <--- line card statsOutput packets 0, bytes 0, drops 0Related Commands
show cef
Displays which packets the line cards dropped or displays which packets were not express forwarded.
show cef interface
Displays CEF-related interface information.
show ip cef
To display entries in the FIB that are unresolved or to display a summary of the FIB, use this form of the show ip cef EXEC command:
show ip cef [unresolved | summary]
To display specific entries in the FIB based on IP address information, use this form of the show ip cef EXEC command:
show ip cef [network [mask [longer-prefix]]] [detail]
To display specific entries in the FIB based on interface information, use this form of the show ip cef EXEC command:
show ip cef [type number] [detail]
Syntax Description
Command Modes
EXEC
Command History
11.2 GS
This command was introduced to support the Cisco 12012 Gigabit Switch Router.
11.1 CC
Multiple platform support was added.
Usage Guidelines
The show ip cef command without any keywords or arguments shows a brief display of all FIB entries.
The show ip cef detail command shows detailed FIB entry information for all FIB entries.
Examples
The following is sample output from the show ip cef unresolved command:
Router# show ip cef unresolvedIP Distributed CEF with switching (Table Version 136632)45776 routes, 13 unresolved routes (0 old, 13 new)45776 leaves, 2868 nodes, 8441480 bytes, 136632 inserts, 90856 invalidations1 load sharing elements, 208 bytes, 1 references1 CEF resets, 1 revisions of existing leavesrefcounts: 527292 leaf, 465617 node148.214.0.0/16, version 1366220 packets, 0 bytesvia 171.69.233.56, 0 dependencies, recursiveunresolved148.215.0.0/16, version 1366230 packets, 0 bytesvia 171.69.233.56, 0 dependencies, recursiveunresolved148.218.0.0/16, version 1366240 packets, 0 bytesTable 102 describes the significant fields shown in the display.
The following is sample output from the show ip cef summary command:
Router# show ip cef summaryIP Distributed CEF with switching (Table Version 135165)45788 routes, 0 reresolve, 4 unresolved routes (0 old, 4 new)45788 leaves, 2868 nodes, 8442864 bytes, 135165 inserts, 89377 invalidations0 load sharing elements, 0 bytes, 0 references1 CEF resets, 0 revisions of existing leavesrefcounts: 527870 leaf, 466167 nodeFor a description of significant fields in this display, see Table 102.
The following is sample output from the show ip cef internal command; it shows load-sharing details for multiple paths to a prefix. The loadshare table in the example shows load distribution 0 1 0 1 . . . , and traffic share is 1 for each route. This means an equal cost per-destination load sharing between two equal cost routes.
Router# show ip cef 192.168.1.0 internal192.168.1.0/24, version 135490, per-destination sharing0 packets, 0 bytesvia 172.19.233.50, 0 dependencies, recursive <-- possible path 1 infotraffic share 1, current pathnext hop 172.19.233.50, Ethernet0/0 via 172.19.233.50/32valid adjacencyvia 172.19.233.49, 0 dependencies, recursive <-- possible path 2 infotraffic share 1next hop 172.19.233.49, Ethernet0/0 via 172.19.233.49/32valid adjacency0 packets, 0 bytes switched through the prefixLoad distribution: 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 (refcount 1) ^!.. how the load is distributed among the possible pathsHash OK Interface Address Packets1 Y Ethernet0/0 172.19.233.50 02 Y Ethernet0/0 172.19.233.49 03 Y Ethernet0/0 172.19.233.50 04 Y Ethernet0/0 172.19.233.49 05 Y Ethernet0/0 172.19.233.50 06 Y Ethernet0/0 172.19.233.49 07 Y Ethernet0/0 172.19.233.50 08 Y Ethernet0/0 172.19.233.49 09 Y Ethernet0/0 172.19.233.50 010 Y Ethernet0/0 172.19.233.49 011 Y Ethernet0/0 172.19.233.50 012 Y Ethernet0/0 172.19.233.49 013 Y Ethernet0/0 172.19.233.50 014 Y Ethernet0/0 172.19.233.49 015 Y Ethernet0/0 172.19.233.50 016 Y Ethernet0/0 172.19.233.49 0The following is sample output from the show ip cef detail command for Ethernet interface 0. It shows all the prefixes resolving through adjacency pointing to next hop Ethernet interface 0/0 and next-hop interface IP address 172.19.233.33.
Router# show ip cef e0/0 172.19.233.33 detailIP Distributed CEF with switching (Table Version 136808)45800 routes, 8 unresolved routes (0 old, 8 new) 45800 leaves, 2868 nodes, 8444360 bytes, 136808 inserts, 91008 invalidations 1 load sharing elements, 208 bytes, 1 references 1 CEF resets, 1 revisions of existing leaves refcounts: 527343 leaf, 465638 node172.19.233.33/32, version 7417, cached adjacency 172.19.233.33 0 packets, 0 bytes, Adjacency-prefixvia 172.19.233.33, Ethernet0/0, 0 dependenciesnext hop 172.19.233.33, Ethernet0/0valid cached adjacencyTable 103 describes the significant fields in the display.
Related Commands
show cef
Displays which packets the line cards dropped or displays which packets were not express forwarded.
show cef interface
Displays CEF-related interface information.
