Table Of Contents
ip cef table adjacency-prefix override
ip cef table consistency-check
ip cef accounting
To enable Cisco Express Forwarding (CEF) network accounting, use the ip cef accounting command in global configuration mode or interface configuration mode. To disable network accounting of CEF, use the no form of this command.
ip cef accounting {[non-recursive] [per-prefix] [prefix-length]}
no ip cef accounting {[non-recursive] [per-prefix] [prefix-length]}
Specific CEF Accounting Information Through Interface Configuration Mode
ip cef accounting non-recursive {external | internal}
no ip cef accounting non-recursive {external | internal}
Syntax Description
Defaults
Accounting is disabled by default.
Command Modes
Global configuration
Interface configuration
Command History
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 (RP) when CEF mode is enabled and at the line cards when distributed CEF (dCEF) mode is enabled. You can then display the collected accounting information using the show ip cef privileged EXEC command.
For prefixes with directly connected next hops, the non-recursive keyword enables the collection of packets and bytes to be express forwarded through a prefix. This keyword is optional when this command is used in global configuration mode.
This command in interface configuration mode must be used in conjunction with the global configuration command. The interface configuration command allows a user to specify two different bins (internal or external) for the accumulation of statistics. The internal bin is used by default. The statistics are displayed through the show ip cef detail command.
Examples
The following example shows how to enable the collection of CEF accounting information:
Router(config)# ip cef accountingRelated Commands
ip cef linecard ipc memory
To configure the line card memory pool for the Cisco Express Forwarding (CEF) queuing messages, use the ip cef linecard ipc memory command in global configuration mode. To return to the default Inter-process Communications (IPC) memory allocation, use the no form of this command.
ip cef linecard ipc memory kbps
no ip cef linecard ipc memory kbps
Syntax Description
Defaults
Default IPC memory allocation is 25 messages. However, this value is dependant on the switching platform.
Command Modes
Global configuration
Command History
Usage Guidelines
This command is available only on distributed switching platforms.
If you are expecting large routing updates to the Route Processor (RP), use this command to allocate a larger memory pool on the line cards for queuing CEF routing update messages. The memory pool reduces the transient memory requirements on the RP.
To display and monitor the current size of the CEF message queues, use the show cef linecard command. Also, the peak size is recorded and displayed when you use the detail keyword.
Examples
The following example shows how to configure the CEF line card memory queue to 128000 kilobytes per second:
Router(config)# ip cef linecard ipc memory 128000Related Commands
show cef linecard
Displays detailed CEF information for the specified line card.
ip cef load-sharing algorithm
To select a Cisco Express Forwarding (CEF) load balancing algorithm, use the ip cef load-sharing algorithm command in global configuration mode. To return to the default universal load balancing algorithm, use the no form of this command.
ip cef load-sharing algorithm {original | tunnel [id] | universal [id]}
no ip cef load-sharing algorithm {original | tunnel [id] | universal [id]}
Syntax Description
Defaults
The universal load sharing algorithm is selected.
Command Modes
Global configuration
Command History
12.0(12)S
This command was introduced.
12.1(5)T
This command was integrated into Cisco IOS Release 12.1(5)T.
Usage Guidelines
The original CEF load sharing algorithm produced distortions in load sharing across multiple routers due to the use of the same algorithm on every router. When the load sharing algorithm is set to universal mode, each router on the network can make a different load sharing decision for each source-destination address pair which resolves load sharing distortions.
The tunnel algorithm is designed to more fairly share load when only a few source-destination pairs are involved.
Examples
The following example shows how to enable the CEF load sharing algorithm for universal environments:
Router(config)# ip cef load-sharing algorithm universal 1Related Commands
debug ip cef hash
Records CEF load sharing hash algorithm events
ip load-sharing
Enables load balancing.
ip cef table adjacency-prefix override
To enable Cisco Express Forwarding (CEF) adjacency prefixes to override static host glean routes, use the ip cef table adjacency-prefix override command in global configuration mode. To disable CEF adjacency prefix override, use the no form of this command.
ip cef table adjacency-prefix override
no ip cef table adjacency-prefix override
Syntax Description
This command has no arguments or keywords.
Defaults
Adjacency prefix override is enabled by default.
Command Modes
Global configuration
Command History
12.0(16)S
This command was introduced.
12.2(2)T
This command was integrated into Cisco IOS Release 12.2(2)T.
Usage Guidelines
When CEF is configured, the forwarding information base (FIB) table may conflict with static host routes that are specified in terms of an output interface and Layer 2 address resolution protocols (Address Resolution Protocol [ARP], map lists, and so on). The Layer 2 address resolution protocol adds adjacencies to CEF, which in turn creates a corresponding host route entry in the FIB table. This entry is called an adjacency prefix. If these adjacency prefix entries are also configured by a static host route, a conflict occurs.
This command ensures that adjacency prefixes can override static host glean routes, and correctly restore routes when the adjacency prefix is deleted.
Examples
The following example shows how to enable CEF table adjacency prefix override:
Router(config)# ip cef table adjacency-prefix overrideip cef table consistency-check
To enable Cisco Express Forwarding (CEF) table consistency checker types and parameters, use the ip cef table consistency-check command in global configuration mode. To disable consistency checkers, use the no form of this command.
ip cef table consistency-check [type {lc-detect | scan-lc | scan-rib | scan-rp}] [count count-number] [period seconds]
no ip cef table consistency-check [type {lc-detect | scan-lc | scan-rib | scan-rp}] [count count-number] [period seconds]
Specific to Suppress Errors During Route Updates
ip cef table consistency-check [settle-time seconds]
no ip cef table consistency-check [settle-time seconds]
Syntax Description
Defaults
All consistency checkers are disabled by default.
Command Modes
Global configuration
Command History
12.0(15)S
This command was introduced.
12.2(2)T
This command was integrated into Cisco IOS Release 12.2(2)T.
Usage Guidelines
This command configures CEF consistency checkers and parameters for the following detection mechanism types:
Examples
The following example shows how to enable the CEF consistency checkers:
Router(config)# ip cef table consistency-checkRelated Commands,
ip cef table event-log
To control Cisco Express Forwarding (CEF) table event-log characteristics, use the ip cef table event-log command in global configuration mode.
ip cef table event-log [size event-number] [match ip-prefix mask]
no ip cef table event-log [size event-number] [match ip-prefix mask]
Specific to Virtual Private Network (VPN) Event Log
ip cef table event-log [size event-number] [vrf vrf-name] [match ip-prefix mask]
no ip cef table event-log [size event-number] [vrf vrf-name] [match ip-prefix mask]
Syntax Description
Defaults
Default size for event log is 10000 entries.
Command Modes
Global configuration
Command History
12.0(15)S
This command was introduced.
12.2(2)T
This command was integrated into Cisco IOS Release 12.2(2)T.
Usage Guidelines
This command is used to troubleshoot inconsistencies that occur in the CEF event log between the routes in the Routing Information Base (RIB), Route Processor (RP) CEF tables, and line card CEF tables.
The CEF event log collects CEF events as they occur without debugging enabled. This process allows the tracing of an event immediately after it occurs. Cisco technical personnel may ask for information from this event log to aid in resolving problems with the CEF feature.
When the CEF table event log has reached its capacity, the oldest event is written over by the newest event until the event log size is reset using this command or cleared using the clear ip cef event-log command.
Examples
The following example shows how to set the CEF table event log size to 5000 entries:
Router(config)# ip cef table event-log size 5000Related Commands
ip cef table resolution-timer
To change the Cisco Express Forwarding (CEF) background resolution timer, use the ip cef table resolution-timer command in global configuration mode.
ip cef table resolution-timer seconds
no ip cef table resolution-timer seconds
Syntax Description
seconds
Timer value in seconds. Range is from 0 to 30 seconds; 0 is for the automatic exponential backoff scheme.
Defaults
The default configuration value is 0 seconds for automatic exponential backoff.
Command Modes
Global configuration
Command History
Usage Guidelines
The CEF background resolution timer can use either a fixed time interval or an exponential backoff timer that reacts to the amount of resolution work required. The exponential backoff timer starts at 1 second, increasing to 16 seconds when a network flap is in progress. When the network recovers, the timer returns to 1 second.
The default is used for the exponential backoff timer. During normal operation, the default configuration value set to 0 results in re-resolution occurring much sooner than when the timer is set at a higher fixed interval.
Examples
The following example show how to set the CEF background resolution timer to 3 seconds:
Router(config)# ip cef table resolution-timer 3ip cef
To enable Cisco Express Forwarding (CEF) on the route processor card, use the ip cef command in global configuration mode. 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
CEF is disabled by default, excluding these platforms:
CEF is enabled on the Cisco 7100 series router.
CEF is enabled on the Cisco 7200 series router.
CEF is enabled on the Cisco 7500 series Internet router.
Distributed CEF is enabled on the Cisco 6500 series router
Distributed CEF is enabled on the Cisco 12000 series Internet router.Command Modes
Global configuration
Command History
Usage Guidelines
The ip cef command is not available on the Cisco 12000 series because that router series operates only in dCEF 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.
If you enable CEF and then create an access list that uses the log keyword, the packets that match the access list are not CEF switched. They are fast switched. Logging disables CEF.
Examples
The following example shows how to enable standard CEF operation:
Router(config)# ip cefThe following example shows hos to enables dCEF operation:
Router(config)# ip cef distributedRelated Commands
ip load-sharing
To enable load balancing for Cisco Express Forwarding (CEF), use the ip load-sharing command in interface configuration mode.
ip load-sharing [per-packet] [per-destination]
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.
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-packet load balancing via CEF is not supported on Engine 2 Gigabit Switch Router (GSR) line cards (LCs).
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 shows how to enable per-packet load balancing:
Router(config)# interface E0Router(config-if)# ip load-sharing per-packetThe following example shows how to enable per-destination load balancing:
Router(config)# interface E0Router(config-if)# ip load-sharing per-destinationRelated Commands
ip route-cache
To control the use of high-speed switching caches for IP routing, use the ip route-cache command in interface configuration mode. To disable any of these switching modes, use the no form of this command.
IP Route-Cache
ip route-cache
no ip route-cache
IP Route-Cache Same-Interface
ip route-cache same-interface
no ip route-cache same-interface
IP Route-Cache Flow
ip route-cache [flow]
no ip route-cache [flow]
IP Route-Cache Distributed
ip route-cache distributed
no ip route-cache distributed
IP Route-Cache CEF
ip route-cache cef
no ip route-cache cef
Syntax Description
Defaults
Fast switching varies by interface and media.
Distributed switching is disabled.
When CEF or dCEF operation is enabled globally, all interfaces that support CEF or dCEF are enabled by default.
Command Modes
Interface configuration
Command History
10.0
This command was introduced.
11.2 GS
The cef and distributed keywords were added.
11.1 CC
Multiple platform support was added for cef keyword.
Usage Guidelines
IP Route-Cache
Using the route cache is often called fast switching. The route cache allows outgoing packets to be load-balanced on a per-destination basis rather than on a per-packet basis. The ip route-cache command with no additional keywords enables fast switching.
Entering the ip route-cache command has no effect on a subinterface. Subinterfaces accept the no form of the command; however, this disables CEF or dCEF on the physical interface as well as all subinterfaces associated with the physical interface.
IP Route-Cache Same-Interface
You can enable IP fast switching when the input and output interfaces are the same interface, using the ip route-cache same-interface command. This configuration normally is not recommended, although it is useful when you have partially meshed media, such as Frame Relay or you are running Web Cache Communication Protocol (WCCP) redirection. You could use this feature on other interfaces, although it is not recommended because it would interfere with redirection of packets to the optimal path.
IP Route-Cache Flow
The flow caching option can be used in conjunction with CEF switching to allow statistics to be gathered with a finer granularity. The statistics include IP subprotocols, well-known ports, total flows, average number of packets per flow, and average flow lifetime.
IP Route-Cache Distributed
The distributed option is supported on Cisco routers with line cards and Versatile Interface Processors (VIPs) that support both CEF and flow switching.
On Cisco routers with Route Switch Processor (RSP) and VIP controllers, the VIP hardware can be configured to switch packets received by the VIP with no per-packet intervention on the part of the RSP. When VIP distributed switching is enabled, the input VIP interface tries to switch IP packets instead of forwarding them to the RSP for switching. Distributed switching helps decrease the demand on the RSP.
If the ip route-cache distributed, ip cef distributed, and ip route-cache flow commands are configured, the VIP will perform distributed CEF switching and collect a finer granularity of flow statistics.
IP Route-Cache CEF
In some instances, 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. Because all interfaces that support CEF or dCEF are enabled by default when you enable CEF operation globally, you must use the no form of the ip route-cache cef command in the interface configuration mode to turn CEF operation off a particular interface. To reenable CEF or dCEF operation, use the ip route-cache cef command.
Disabling CEF or dCEF on an interface disables CEF switching for packets forwarded to the interface, but has no affect on packets forwarded out of the interface.
Additionally 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 RSP.
Note
Note
Examples
The following example shows how to enable fast switching and disable distributed switching:
Router(config-if)# ip route-cacheThe following example shows how to disable all switching modes except for processor switching.
Router(config-if)# no ip route-cacheThe following example shows how to enable VIP distributed flow switching on the interface:
Router(config)# interface e0Router(config-if)# ip address 17.252.245.2 255.255.255.0Router(config-if)# ip route-cache distributedRouter(config-if)# ip route-cache flowThe following example shows how to enable CEF operation on the router (globally), but it turns off CEF operation on Ethernet interface 0:
Router(config)# ip cefRouter(config)# interface e0Router(config-if)# no ip route-cache cefThe following example shows how to enable dCEF operation on the router (globally), but it turns off CEF operation on Ethernet interface 0:
Router(config)# ip cef distributedRouter(config)# interface e0Router(config-if)# no ip route-cache cefThe following example shows how to reenable dCEF operation on Ethernet interface 0:
Router(config)# ip cef distributedRouter(config)# interface e0Router(config-if)# ip route-cache distributedRelated Commands
