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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.
To clear the Cisco Express Forwarding (CEF) adjacency table, use the clear adjacency EXEC command.
clear adjacencyThis command has no arguments or keywords.
EXEC
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
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.
The following example clears the adjacency table:
clear adjacency
You can use the master indexes or search online to find documentation of related commands.
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]
slot-number | (Optional) Line card slot number to clear. When you omit this argument, all line card slots are cleared. |
adjacency | (Optional) Clears line card adjacency tables and rebuilds adjacency for the specified line card. |
interface | (Optional) Clears line card interface information and re-creates the interface information for the specified line card. |
prefix | (Optional) Clears line card prefix tables and starts rebuilding the FIB table. |
EXEC
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
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.
The following example clears the CEF information from the line cards:
clear cef linecard
You can use the master indexes or search online to find documentation of related commands.
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
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. |
EXEC
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
The following example resets the CEF packet and byte count to zero:
clear ip cef prefix-statistics
You can use the master indexes or search online to find documentation of related commands.
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]
distributed | (Optional) Enables distributed CEF (dCEF) operation. Distributes CEF information to line cards. Line cards perform express forwarding. |
| On this platform... | The default is... |
|---|---|
Cisco 7000 series equipped with RSP7000 | CEF is not enabled. |
Cisco 7200 series | CEF is not enabled. |
Cisco 7500 series | CEF is enabled. |
Cisco 12000 series Gigabit Switch Router | Distributed CEF is enabled. |
Global configuration
This command first appeared in Cisco IOS Release 11.1 CC.
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.
The following example enables standard CEF operation:
ip cef
The following example enables dCEF operation:
ip cef distributed
You can use the master indexes or search online to find documentation of related commands.
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]
per-prefix | (Optional) Enables the collection of the number of packets and bytes express forwarded to a destination (or prefix). |
non-recursive | (Optional) Enables accounting through non-recursive prefixes. For prefixes with directly connected next hops, enables the collection of the number of packets and bytes express forwarded through a prefix. |
Accounting is disabled by default.
Global configuration
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
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.
The following example enables the the collection of CEF accounting information:
ip cef accounting
You can use the master indexes or search online to find documentation of related commands.
To change the time interval that controls when NHRP will set up or tear down an SVC, 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]
load-interval seconds | (Optional) Length of time (in 30-second increments) during which the average trigger-threshold and teardown-threshold are calculated before an SVC setup or teardown action is taken. (These thresholds are configured in the ip nhrp trigger-svc command.) The load-interval range is 30 seconds to 300 seconds, in 30-second increments. The default value is 30 seconds. |
update-rate seconds | (Optional) Frequency that the port adapter sends the accounting statistics to the RP. When using NHRP in distributed CEF switching mode, this value must be set to 5 seconds. The default value is 10 seconds. |
load-interval: 30 seconds
update-rate: 10 seconds
Global configuration
This command first appeared in Cisco IOS Release 12.0.
The thresholds in the ip nhrp trigger-svc command must be exceeded during a certain time interval, which is 30 seconds by default. To change that interval, use the load-interval seconds argument of the ip cef traffic-statistics command.
When NHRP is configured on a CEF switching node with a VIP2 adapter, you must make sure the update-rate is set to 5 seconds.
Other features could also use the ip cef traffic-statistics command; this NHRP feature relies on it.
In the following example, the triggering and teardown thresholds are calculated based on an average over 120 seconds:
ip cef traffic-statistics load-interval 120
You can use the master indexes or search online to find documentation of related commands.
ip nhrp trigger-svc
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]
per-packet | (Optional) Enables per-packet load balancing on the interface. |
per-destination | (Optional) Enables per-destination load balancing on the interface. |
Per-destination load balancing is enabled by default when you enable CEF.
Interface configuration
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
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.
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.
The following example enables per-packet load balancing:
interface E0 ip load-sharing per-packet
The following example enables per-destination load balancing:
interface E0 ip load-sharing per-destination
You can use the master indexes or search online to find documentation of related commands.
interface
ip cef
This command has no arguments or keywords.
When standard CEF or dCEF operation is enabled globally, all interfaces that support CEF are enabled by default.
Interface configuration
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
Cisco Express Forwarding (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.
The following example enables CEF operation on the router (globally), but turns off CEF operation on Ethernet interface 0:
ip cef interface e0 no ip route-cache cef
The following example enables dCEF operation on the router (globally), but turns off CEF operation on Ethernet interface 0:
ip cef distributed interface e0 no ip route-cache cef
The following example reenables dCEF operation on Ethernet interface 0:
ip cef distributed interface e0 ip route-cache cef
You can use the master indexes or search online to find documentation of related commands.
interface
ip cef
To display Cisco Express Forwarding (CEF) adjacency table information, use the show adjacency EXEC command.
show adjacency [detail]
detail | (Optional) Displays detailed adjacency information, including Layer 2 information. |
EXEC
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
This command is available only on routers that have RP cards.
The following is sample output from the show adjacency detail command:
Router# show adjacency detail
Protocol Interface Address IP Tunnel0 point2point(3) (incomplete) 0 packets, 0 bytes FIB 00:02:45 IP Ethernet1/0/0 192.168.177.15(6) 0 packets, 0 bytes 0060837BEFA0 Protocol Interface Address 0060836FA7000800 ARP 03:59:44 igrp 622 00:04:14 IP Ethernet0/0 192.168.233.88(5) 0 packets, 0 bytes 0060837BEFA0 0060836FA7000800 ARP 03:59:36 IP FastEthernet2/0/0 172.16.1.106 (11) (incomplete) 0 packets, 0 bytes IP FastEthernet2/0/0 172.26.1.106 (11) (incomplete) 0 packets, 0 bytes
Table 8 describes the fields shown in the output.
| Field | Description |
|---|---|
Protocol | The routing protocol configured on the interface. |
Interface | The type of interface configured. |
Address | The address of the interface. |
Routing protocol | The method by which the adjacency was learned. |
Adjacent next hop | The MAC address of the adjacent router. |
Time stamp | The time left before the adjacency rolls out of the adjacency table. Once it rolls out, a packet must use the same next hop to the destination. |
You can use the master indexes or search online to find documentation of related commands.
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]
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. |
EXEC
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
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.
The following is sample output from the show cef drop command:
Router# show cef drop
CEF Drop Statistics Slot Encap_fail Unresolved Unsupported No_route No_adj ChksumErr RP 4 89 0 4 0 0 1 0 0 0 0 0 0 2 0 0 5 0 0 5
Table 9 describes the fields shown in the output.
| Field | Description |
|---|---|
Slot | The slot number on which the packets were received. |
Encap_fail | Indicates the number of packets dropped after the limit was reached for incomplete packets with no adjacency route. |
Unresolved | Indicates the number of packets dropped because the route for the prefix was not resolved. |
Unsupported | Indicates the number of packets received for which the adjacency route information was dropped due to unsupported features. |
No_route | No route definition is included in the prefix table. |
No_adj | The prefix is resolved, but the adjacent route is not indicated. |
ChksumErr | Indicates the number of packets received with a checksum error. |
The following is sample output from the show cef not-cef-switched command:
Router# show cef not-cef-switched
CEF Packets passed on to next switching layer Slot No_adj No_encap Unsuppted Redirect Receive Bad_ttl Options Access RP 0 0 0 0 91584 0 0 0 1 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0
Table 10 describes the fields shown in the output.
| Field | Meaning |
|---|---|
No_adj | Indicates the number of packets sent to the line card to ARP for the adjacent route. |
No_encap | Number of encapsulated packets received. |
Unsupported Redirect | Number of packets with unsupported features and redirected to another switching layer or location for processing. |
You can use the master indexes or search online to find documentation of related commands.
show cef interface
show cef linecard
To display Cisco Express Forwarding (CEF) related interface information, use the show cef interface EXEC command.
show cef interface type number [detail]
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. |
EXEC
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
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.
The following is sample output from the show cef interface detail command for Ethernet interface 0:
Router# show cef interface E0 detail
Ethernet1/0/0 is up (if_number 6) Internet address is 172.19.177.20/24 ICMP redirects are always sent Per-packet load balancing is disabled Inbound access list is 10 Outbound access list is not set Hardware idb is Ethernet1/0/0 Fast switching type 1, interface type 5 IP Distributed CEF switching enabled IP Feature CEF switching turbo vector Fast flags 0x4. ifindex 5(5) Slot 1 Slot unit 0 VC -1 Hardware transmit queue ptr 0x48001A00 (0x48001A00) >- debugging purposes Transmit limit accumulator 0x48001A02 (0x48001A02) IP MTU 1500
Table 11 describes the fields shown in the output.
| Field | Description |
|---|---|
interface type number is {up | down} | Indicates status of the interface. |
Internet address | Internet address of the interface |
ICMP packets are {always sent | never sent} | Indicates how packet forwarding is configured. |
Per-packet load balancing | Status of load balancing in use on the interface (enabled or disabled). |
Inbound access list {# | Not set} | Number of access lists defined for the interface. |
Outbound access list | Number of access lists defined for the interface. |
Hardware idb is type number | Interface type and number configured. |
Fast switching type | Used for troubleshooting; indicates switching mode in use. |
IP Distributed CEF switching {enabled | disabled} | Indicates the switching path used. |
Slot n Slot unit n | The slot number. |
Hardware transmit queue | Indicates the number of packets in the transmit queue. |
Transmit limit accumulator | Indicates the maximum number of packets allowed in the transmit queue. |
IP MTU | The value of the MTU size set on the interface. |
You can use the master indexes or search online to find documentation of related commands.
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]
slot-number | (Optional) Slot number containing the line card about which to display CEF-related information. When you omit this argument, information about all line cards is displayed. |
detail | (Optional) Displays detailed CEF information for the specified line card. |
EXEC
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
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.
The following is sample output from the show cef linecard command. The command displays information for the line cards.
Router# show cef linecard
CEF table version 115705, 45877 routes Slot CEF-ver MsgSent XdrSent Seq MaxSeq LowQ HighQ Flags 1 238 668 9641 616 616 0 0 up, sync 2 238 683 10782 619 629 0 0 up, sync
Table 12 describes the fields shown in the output.
| Field | Description |
|---|---|
CEF table version | The FIB table version. |
XdrSent | IPC information elements (xdrs) packed into IPC messages sent from the RP to the line card. |
MsgSent | Number of IPC messages sent. |
Seq | Sequence number for the line card. |
MaxSeq | Maximum sequence expected by the line card. |
LowQ/HighQ | Number of xdr elements in LowQ and HighQ. |
Flags | Indicates the status of the line card. Possible states are
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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 detail
CEF line card slot number 2, status up, sync, disabled line card CEF version number 238 Sequence number 616, Maximum sequence number expected 616 Send failed 0, Out Of Sequence 0 line card CEF reset 2, reloaded 2 92299/15/91 prefix/adjacency/interface elements queued 49641 elements packed in 668 messages(1341286 bytes) sent 0/0 xdr elements in LowQ/HighQ Input packets 0, bytes 0 <--- line card stats Output packets 0, bytes 0, drops 0
You can use the master indexes or search online to find documentation of related commands.
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]
unresolved | (Optional) Displays unresolved FIB entries. |
summary | (Optional) Displays a summary of the FIB. |
network | (Optional) Displays the FIB entry for the specified destination network. |
mask | (Optional) Displays the FIB entry for the specified destination network and mask. |
longer-prefix | (Optional) Displays FIB entries for all more specific destinations. |
detail | (Optional) Displays detailed FIB entry information. |
type number | (Optional) Interface type and number for which to display FIB entries. |
EXEC
This command first appeared to support the Cisco 12012 Gigabit Switch Router in Cisco IOS Release 11.2 GS, and first appeared with multiple platform support in Cisco IOS Release 11.1 CC.
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.
The following is sample output from the show ip cef unresolved command:
Router# show ip cef unresolved
IP 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 invalidations 1 load sharing elements, 208 bytes, 1 references 1 CEF resets, 1 revisions of existing leaves refcounts: 527292 leaf, 465617 node 148.214.0.0/16, version 136622 0 packets, 0 bytes via 171.69.233.56, 0 dependencies, recursive unresolved 148.215.0.0/16, version 136623 0 packets, 0 bytes via 171.69.233.56, 0 dependencies, recursive unresolved 148.218.0.0/16, version 136624 0 packets, 0 bytes
The following is sample output from the show ip cef summary command:
Router# show ip cef summary
IP 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 invalidations 0 load sharing elements, 0 bytes, 0 references 1 CEF resets, 0 revisions of existing leaves refcounts: 527870 leaf, 466167 node
The following is sample output from the show ip cef internal command; it shows load-sharing details for multiple paths to a prefix:
Router# show ip cef 192.168.1.0 internal
192.168.1.0/24, version 135490, per-destination sharing 0 packets, 0 bytes via 172.19.233.50, 0 dependencies, recursive <-- possible path 1 info traffic share 1, current path next hop 172.19.233.50, Ethernet0/0 via 172.19.233.50/32 valid adjacency via 172.19.233.49, 0 dependencies, recursive <-- possible path 2 info traffic share 1 next hop 172.19.233.49, Ethernet0/0 via 172.19.233.49/32 valid adjacency 0 packets, 0 bytes switched through the prefix Load 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 paths Hash OK Interface Address Packets 1 Y Ethernet0/0 172.19.233.50 0 2 Y Ethernet0/0 172.19.233.49 0 3 Y Ethernet0/0 172.19.233.50 0 4 Y Ethernet0/0 172.19.233.49 0 5 Y Ethernet0/0 172.19.233.50 0 6 Y Ethernet0/0 172.19.233.49 0 7 Y Ethernet0/0 172.19.233.50 0 8 Y Ethernet0/0 172.19.233.49 0 9 Y Ethernet0/0 172.19.233.50 0 10 Y Ethernet0/0 172.19.233.49 0 11 Y Ethernet0/0 172.19.233.50 0 12 Y Ethernet0/0 172.19.233.49 0 13 Y Ethernet0/0 172.19.233.50 0 14 Y Ethernet0/0 172.19.233.49 0 15 Y Ethernet0/0 172.19.233.50 0 16 Y Ethernet0/0 172.19.233.49 0
The 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 detail
IP 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 node 172.19.233.33/32, version 7417, cached adjacency 172.19.233.33 0 packets, 0 bytes, Adjacency-prefix via 172.19.233.33, Ethernet0/0, 0 dependencies next hop 172.19.233.33, Ethernet0/0 valid cached adjacency
You can use the master indexes or search online to find documentation of related commands.
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