IP Routing Protocol-Independent Commands: A through R

To set the time period during which the authentication key on a key chain is received as valid, use the accept-lifetimecommand inkey chain key configuration mode. To revert to the default value, use the no form of this command.

Syntax Description

Command Default

The authentication key on a key chain is received as valid forever (the starting time is January 1, 1993, and the ending time is infinite).

Command Modes

Key chain key configuration (config-keychain-key)

Command History

Usage Guidelines

Only DRP Agent, Enhanced Interior Gateway Routing Protocol (EIGRP), and Routing Information Protocol ( RIP) Version 2 use key chains.

Specify a start-time value and one of the following values: infinite, end-time, or duration seconds.

We recommend running Network Time Protocol (NTP) or some other time synchronization method if you assign a lifetime to a key.

If the last key expires, authentication will continue and an error message will be generated. To disable authentication, you must manually delete the last valid key.

Related Commands

To configure authentication in a Bidirectional Forwarding Detection (BFD) template for single hop and multihop sessions, use the authentication command in BFD configuration mode. To disable authentication in BFD template for single-hop and multihop sessions, use the no form of this command.

Syntax Description

Command Default

Authentication in BFD template for single hop and multihop sessions is not enabled.

Command Modes

BFD configuration (config-bfd)

Command History

Usage Guidelines

You can configure authentication in single hop and multihop templates. We recommend that you configure authentication to enhance security. Authentication must be configured on each BFD source-destination pair, and authentication parameters must match on both devices.

Related Commands

To set the baseline Bidirectional Forwarding Detection (BFD) session parameters on an interface, use the bfd command in interface configuration mode. To remove the baseline BFD session parameters, use the no form of this command.

Syntax Description

Command Default

No baseline BFD session parameters are set.

Command Modes

Interface configuration (config-if)

Command History

Usage Guidelines

The bfd command can be configured on the following interfaces:

• ATM
• Dot1Q VLAN subinterfaces (with an IP address on the Dot1Q subinterface)
• Ethernet
• Frame Relay
• Inverse Multiplexing over ATM (IMA)
• IP tunnel
• Port channel
• PoS
• Serial
• Tunnel (The tunnel type must be point-to-point, not Multiprotocol Label Switching (MPLS).

If BFD runs on a port channel interface, BFD has a timer value restriction of 750 * 3 milliseconds. Other interface types are not supported by BFD.

Note	The intervalcommand is not supported on ATM and IMA interfaces in Cisco IOS Release 15.0(1)M and later releases.

Related Commands

To enable Bidirectional Forwarding Detection (BFD) for all interfaces participating in the routing process, use the bfd all-interfaces command in router configuration or address family interface configuration mode. To disable BFD for all neighbors on a single interface, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

BFD is disabled on the interfaces participating in the routing process.

Command Modes

Router configuration (config-router)

Address family interface configuration (config-router-af)

Command History

Usage Guidelines

There are two methods to configure routing protocols to use BFD for failure detection. To enable BFD for all interfaces, enter the bfd all-interfaces command in router configuration mode. If you do not want to enable BFD on all interfaces, enter bfd interface command in router configuration mode. In Cisco IOS Release 12.4(24)T, Cisco IOS 12.2(33)SRA, and earlier releases, the bfd all-interfaces command works in router configuration mode and address family interface mode.

In Cisco IOS Release 15.0(1)M and later releases, the bfd all-interfaces command in named router configuration mode is replaced by the bfd command in address family interface configuration mode. Use the bfd command in address family interface configuration mode to achieve the same functionality as that of the bfd all-interfaces command in router configuration mode.

Related Commands

To enable Bidirectional Forwarding Detection (BFD) control plane failure checking for the Intermediate System-to-Intermediate System (IS-IS) routing protocol, use the bfd check-control-plane-failure command in router configuration mode. To disable control plane failure detection, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

BFD control plane failure checking is disabled.

Command Modes

Router configuration (config-router)

Command History

Usage Guidelines

The bfd check-ctrl-plane-failure command can be configured for an IS-IS routing process only. The command is not supported on other protocols.

When a router restarts, a false BFD session failure can occur, where neighboring routers behave as if a true forwarding failure has occurred. However, if the bfd check-ctrl-plane-failure command is enabled on a router, the router can ignore control plane related BFD session failures. We recommend that you add this command to the configuration of all neighboring routers just prior to a planned router restart, and that you remove the command from all neighboring routers when the restart is complete.

Related Commands

To enable Bidirectional Forwarding Detection (BFD) echo mode, use the bfdecho command in interface configuration mode. To disable BFD echo mode, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

BFD echo mode is enabled by default.

Command Modes

Interface configuration (config-if)

Command History

Usage Guidelines

Echo mode is enabled by default. Entering the nobfdecho command without any keywords turns off the sending of echo packets and signifies that the router is unwilling to forward echo packets received from BFD neighbor routers.

When echo mode is enabled, the desired minimum echo transmit interval and required minimum transmit interval values are taken from the bfdintervalmillisecondsmin_rxmilliseconds parameters, respectively.

Note	If the noiproute-cachesame-interface command is configured, the bfdechoaccept command will not be accepted.

Note	Before using BFD echo mode, you must disable the sending of Internet Control Message Protocol (ICMP) redirect messages by entering the noipredirects command, in order to avoid high CPU utilization.

The bfdecho command is not supported on ATM and IMA interfaces Cisco IOS Release 15.0(1)M and later releases.

Echo Mode Without Asymmetry

Echo mode is described as without asymmetry when it is running on both sides (both BFD neighbors are running echo mode).

Related Commands

To enable Bidirectional Forwarding Detection (BFD) on a per-interface basis, use the bfdinterfacecommand in router configuration mode. To disable BFD for all neighbors on a single interface, use the no form of this command.

Syntax Description

Command Default

BFD is not enabled for the interface.

Command Modes

Router configuration (config-router)

Command History

Usage Guidelines

In Cisco IOS Release 12.4(24)T and 12.2(33)SRA and earlier releases, the bfdinterface command works in router configuration mode and address-family intreface mode (af-interface mode).

In Cisco IOS Release 15.0(1)M and later releases, the bfdinterface command in named router configuration mode is replaced by the bfdcommand in address-family interface mode. Use the bfd command in af-interface mode to achieve the same functionality as that of the bfdinterface command in router configuration mode.

Related Commands

To configure a Bidirectional Forwarding Detection (BFD) map that associates timers and authentication with multihop templates, use the bfd map command in global configuration mode. To disable a BFD map, use the no form of this command.

Syntax Description

Command Default

The BFD map does not exist.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

The showbfdneighbors command can be used to help troubleshoot the BFD feature.

The full output for the details keyword is not supported on the Route Processor (RP) for the Cisco 12000 series Internet router. If you want to enter the showbfdneighbors command with the details keyword on the Cisco 12000 series Internet router, you must enter the command on the line card. Use the attachslotcommand to establish a CLI session with a line card.

In Cisco IOS Release 15.1(2)S and later releases that support BFD hardware offload, the Tx and Rx intervals on both BFD peers must be configured in multiples of 50 milliseconds. If they are not, output from the showbfdneighborsdetails command will show the configured intervals, not the changed ones.

See the Configuring Synchronous Ethernet on the Cisco 7600 Router with ES+ Line Card section of the Cisco 7600 Series Ethernet Services Plus (ES+) and Ethernet Services Plus T (ES+T) Line Card Configuration Guide for more information about prerequisites and restrictions for hardware offload.

Usage Guidelines

Cisco IOS Release 15.1(3)S and later releases support BFD on multiple network hops. The bfd-template command configures timers and authentication for a template. The bfd map command associates those timers and authentication with unique source-destination address pairs in multihop BFD sessions. Use the bfd-template command to configure a multihop template and the bfd map command to associate it with a map of destinations and associated BFD timers.

For IPv6 addresses, use X:X:X:X::X format; for IPv4 addresses, use the A.B.C.D. classless interdomain routing (CIDR) notation to represent the mask for both source and destination addresses

Related Commands

To configure the Bidirectional Forwarding Detection (BFD) slow timers value, use the bfdslow-timers command in global configuration mode. This command does not have a no form.

Syntax Description

Command Default

The BFD slow timer value is 1000 milliseconds.

Command Modes

Global configuration (config)

Command History

Related Commands

To bind a single hop Bidirectional Forwarding Detection (BFD) template to an interface, use the bfd template command in interface configuration mode. To unbind single-hop BFD template from an interface, use the no form of this command.

Syntax Description

Command Default

A BFD template is not bound to an interface.

Command Modes

Interface configuration (config-if)

Command History

Usage Guidelines

Even if you have not created the template by using the bfd-template command, you can configure the name of the template under an interface, but the template is considered invalid until you define the template. You do not have to reconfigure the template name again. It becomes valid automatically.

Related Commands

To create a Bidirectional Forwarding Detection (BFD) template and to enter BFD configuration mode, use the bfd-template command in global configuration mode. To remove a BFD template, use the no form of this command.

Syntax Description

Command Default

A BFD template does not exist.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

The bfd-template command allows you to create a BFD template and places the device in BFD configuration mode. The template can be used to specify a set of BFD interval values. BFD interval values specified as part of the BFD template are not specific to a single interface.

The bfd map command associates timers and authentication in multihop templates with unique source-destination address pairs in multihop BFD sessions.

You can configure authentication in single-hop and multihop templates. Although it is not required, authentication is recommended to enhance security.

Related Commands

To configure a device to automatically dampen a flapping session, use the dampening command in interface configuration mode. To disable automatic dampening, use the no form of this command.

Syntax Description

Command Default

This command is disabled by default. To manually configure the timer for the restart-penalty argument, the value for all arguments must be manually entered.

Command Modes

Interface configuration (config-if)

Command History

Usage Guidelines

The IP Event Dampening feature will function on a subinterface but cannot be configured on only the subinterface. Only the primary interface can be configured with this feature. Primary interface configuration is applied to all subinterfaces by default.

When an interface is dampened, the interface is dampened to both IP and Connectionless Network Services (CLNS) routing equally. The interface is dampened to both IP and CLNS because integrated routing protocols such as Intermediate System-to-Intermediate System (IS-IS), IP, and CLNS routing protocols are closely interconnected, so it is impossible to apply dampening separately.

Copying a dampening configuration from virtual templates to virtual access interfaces is not supported because dampening has limited usefulness to existing applications using virtual templates. Virtual access interfaces are released when an interface flaps, and new connections and virtual access interfaces are acquired when the interface comes up and is made available to the network. Because dampening states are attached to the interface, the dampening states would not survive an interface flap.

If the dampeningcommand is applied to an interface that already has dampening configured, all dampening states are reset and the accumulated penalty will be set to 0. If the interface has been dampened, the accumulated penalty will fall into the reuse threshold range, and the dampened interface will be made available to the network. The flap counts, however, are retained.

Related Commands

To configure a device to dampen a flapping Bidirectional Forwarding Detection (BFD) session, use the dampening command in BFD configuration mode. To disable dampening, use the no form of this command.

Syntax Description

Command Default

A flapping BFD session on a device is not dampened.

Command Modes

BFD configuration (config-bfd)

Command History

Related Commands

To define an administrative distance for routes that are inserted into the routing table, use the distance command in router configuration mode. To return the administrative distance to its default distance definition, use the no form of this command.

Syntax Description

Command Default

For information on default administrative distances, see the "Usage Guidelines" section.

Command Modes

Router configuration(config-router)

Command History

Usage Guidelines

The table below lists default administrative distances.

An administrative distance is a rating of the trustworthiness of a routing information source, such as an individual router or a group of routers. Numerically, an administrative distance is an integer from 0 to 255. In general, the higher the value, the lower the trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored.

When the optional access list name is used with this command, it is applied when a network is being inserted into the routing table. This behavior allows filtering of networks according to the IP address of the router that supplies the routing information. This option could be used, for example, to filter possibly incorrect routing information from routers that are not under your administrative control.

The order in which you enter distance commands can affect the assigned administrative distances in unexpected ways. See the "Examples" section for further clarification.

For BGP, the distance command sets the administrative distance of the External BGP (eBGP) route.

The showipprotocols privileged EXEC command displays the default administrative distance for the active routing processes.

Always set the administrative distance from the least to the most specific network.

Note	The weight of a route can no longer be set with the distance command. To set the weight for a route, use a route map.

Related Commands

To filter networks received in updates, use the distribute-listin command in the appropriate configuration mode. To change or cancel the filter, use the no form of this command.

distribute-list [[access-list-number | name] | [prefix prefix-name | gateway gateway-name | [route-map map-tag]] in [interface-type | interface-number]

no distribute-list [ [access-list-number | name] | [prefix prefix-name | gateway gateway-name | [route-map map-tag] ] in [interface-type | interface-number]

Syntax Description

Command Default

Networks received in updates are not filtered.

Command Modes

Router configuration (config-router) Address-family configuration (config-router-af) Address-family topology configuration (config-router-af-topology)

Command History

Usage Guidelines

This command must specify either an access list or a map-tag name of a route map. The route map is supported for OSPF and EIGRP filtering.

The interface-typeand interface-numberarguments cannot be used in address-family configuration mode.

OSPF routes cannot be filtered from entering the OSPF database. If you use this command for OSPF, it only filters routes from the routing table; it does not prevent link-state packets from being propagated.

If a route map is specified, the route map can be based on the following match options:

• match interface
• match ip address
• match ip next-hop
• match ip route-source
• match metric
• match route-type
• match tag

Configure the route map before specifying it in the distribute-listin command.

Release 12.2(33)SRB

If you plan to configure the Multi-Topology Routing (MTR) feature, you must enter the distribute-listincommand in address-family topology configuration mode in order for this OSPF router configuration command to become topology-aware.

Related Commands

To suppress networks from being advertised in updates, use the distribute-listout command in the appropriate configuration mode.To cancel this function, use the no form of this command.

Syntax Description

Command Default

This command is disabled by default. Networks are advertised in updates.

Command Modes

Router configuration (config-router) Address-family configuration (config-router-af) Address-family topology configuration (config-router-af-topology)

Command History

Usage Guidelines

When networks are redistributed, a routing process name can be specified as an optional trailing argument to the distribute-list command. Specifying this option causes the access list to be applied to only those routes derived from the specified routing process. After the process-specific access list is applied, any access list specified by a distribute-list command without a process name argument will be applied. Addresses not specified in thedistribute-listcommand will not be advertised in outgoing routing updates.

The interface-nameargument cannot be used in address-family configuration mode.

Note	To filter networks that are received in updates, use the distribute-listin command.

Release 12.2(33)SRB

If you plan to configure the Multi-Topology Routing (MTR) feature, you must enter the distribute-listoutcommand in address-family topology configuration mode in order for this OSPF router configuration command to become topology-aware.

Related Commands

To disable Fast Reroute (FRR) load sharing of prefixes, use the fast-reroute load-sharing disable command in router configuration mode. To restore the default setting, use the no form of this command.

Syntax Description

Command Default

Load sharing of prefixes is enabled by default.

Command Modes

Router configuration (config-router)

Command History

Usage Guidelines

You must configure the router isis command before you can configure the fast-reroute load-sharing disable command.

Load sharing equally distributes the prefixes that use the same protected primary path over the available loop-free alternates (LFAs). An LFA is a next hop that helps a packet reach its destination without looping back.

Related Commands

To enable Fast Reroute (FRR) per prefix, use the fast-reroute per-prefix command in router configuration mode. To disable the configuration, use the no form of this command.

Syntax Description

Command Default

Fast Reroute per prefix is disabled.

Command Modes

Router configuration (config-router)

Command History

Usage Guidelines

You must configure the router isis command before you can configure the fast-reroute per-prefix command.

You must configure the all keyword to protect all prefixes or configure the route-map route-map-name keyword and argument pair to protect a selected set of prefixes. When you specify the all keyword, all paths are protected, except paths that use interfaces, which are not supported, or interfaces, which are not enabled for protection. Using the route-map route-map-name keyword and argument pair to specify protected routes provides you with the flexibility to select protected routes, including using administrative tags.

Repair paths forward traffic during a routing transition. Repair paths are precomputed in anticipation of failures so that they can be activated when a failure is detected.

Related Commands

To configure the Fast Reroute (FRR) tiebreaking priority, use the fast-reroute tie-break command in router configuration mode. To disable the configuration, use the no form of this command.

Syntax Description

Command Default

Tiebreaking is enabled by default.

Command Modes

Router configuration (config-router)

Command History

Usage Guidelines

You must configure the router isis command before you can configure the fast-reroute tie-break command.

Tiebreaking configurations are applied per IS-IS instance per address family. The lower the configured priority value, the higher the priority of the rule. The same attribute cannot be configured more than once in the same address family.

The default tiebreaking rules have a priority value of 256. Hence, the tiebreaking rules that you configure will always have a higher priority than the default rule.

Load sharing equally distributes the prefixes that use the same protected primary path over the available LFAs. An LFA is a next hop that helps a packet reach its destination without looping back.

Related Commands

To enable Bidirectional Forwarding Detection (BFD) echo mode under a BFD template, use the echo command in BFD configuration mode. To disable BFD echo mode, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

BFD echo mode is disabled.

Command Modes

BFD configuration (config-bfd)

Command History

Usage Guidelines

Echo mode is disabled by default. Entering the echo command enables the sending of echo packets and signifies that the device is can forward echo packets received from BFD neighbor devices.

When echo mode is enabled, the desired minimum echo transmit interval and required minimum transmit interval values are derived from the values configured through the interval milliseconds min-rx milliseconds command.

Note	If you configure the no iproute-cache same-interface command, the echo command is rejected.

Note	Before using echo mode, you must disable the sending of Internet Control Message Protocol (ICMP) redirect messages by entering the no ip redirects command, in order to avoid high CPU utilization.

When echo mode is enabled on both BFD neighbors, the echo mode is described as without asymmetry.

Related Commands

To configure the transmit and receive intervals betweenBidirectional Forwarding Detection (BFD) packets, and to specify the number of consecutive BFD control packets that must be missed before BFD declares that a peer is unavailable, use the intervalcommand in BFD configuration mode. To disable interval values use the no form of this command.

Syntax Description

Command Default

No session parameters are set.

Command Modes

BFD configuration (config-bfd)

Command History

Usage Guidelines

The interval command allows you to configure the session parameters for a BFD template.

Related Commands

To select a network as a candidate route for computing the gateway of last resort, use the ip default-network command in global configuration mode. To remove a route, use the no form of this command.

Syntax Description

Command Default

If the router has a directly connected interface to the specified network, the dynamic routing protocols running on that router will generate (or source) a default route. For the Routing Information Protocol (RIP), this route flagged as the pseudo network 0.0.0.0.

Command Modes

Global configuration (config#)

Command History

Usage Guidelines

The Cisco IOS software uses both administrative distance and metric information to determine the default route. Multiple ip default-network commands can be used. All candidate default routes, both static (that is, flagged by the ip default-network command) and dynamic, appear in the routing table preceded by an asterisk.

If the IP routing table indicates that the specified network number is subnetted with a nonzero subnet number, the system will automatically configure a static summary route instead of a default route. The static summary route uses the specified subnet to route traffic destined for subnets that are not explicitly listed in the IP routing table to be routed.

The ip default-network command is a classful command. It is effective only if the network mask of the network that you wish to configure as a candidate route for computing the gateway of last resort matches the network mask in the Routing Information Base (RIB).

For example, if you configure ip default-network 10.0.0.0 , then the mask considered by the routing protocol is 10.0.0.0/8, as it is a Class A network. The gateway of last resort is set only if the RIB contains a 10.0.0.0/8 route.

If you need to use the ip default-network command, ensure that the RIB contains a network route that matches the major mask of the network class.

Related Commands

To configure the router discovery mechanism, use the ipgdp command in global configuration mode. To disable the configuration, use the no form of this command.

Syntax Description

Command Default

The router discovery mechanism is not configured.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

You must disable IP routing to configure the ipgdp command.

Related Commands

To identify a route map to use for local policy routing, use the iplocalpolicyroute-map command in global configuration mode. Todisable local policy routing, use the noform of this command.

Syntax Description

Command Default

Packets that are generated by the router are not policy routed.

Command Modes

Global configuration

Command History

Usage Guidelines

Packets that are generated by the router are not normally policy routed. However, you can use this command to policy route such packets. You might enable local policy routing if you want packets originated at the router to take a route other than the obvious shortest path.

The iplocalpolicyroute-map command identifies a route map to use for local policy routing. Each route-map command has a list of matchand set commands associated with it. The match commands specify the matchcriteria--the conditions under which packets should be policy routed. The set commands specify the setactions--the particular policy routing actions to perform if the criteria enforced by the match commands are met. The noiplocalpolicyroute-mapcommand deletes the reference to the route map and disables local policy routing.

Related Commands

To identify a route map to use for policy routing on an interface, use the ippolicyroute-map command in interface configuration mode. Todisable policy routing on the interface, use the noform of this command.

Syntax Description

Command Default

No policy routing occurs on the interface.

Command Modes

Interface configuration

Command History

Usage Guidelines

You might enable policy routing if you want your packets to take a route other than the obvious shortest path.

The ippolicyroute-map command identifies a route map to use for policy routing. Eachroute-mapcommand has a list of match and set commands associated with it. The match commands specify the matchcriteria--the conditions under which policy routing is allowed for the interface, based on the destination IP address of the packet. The set commands specify the setactions--the particular policy routing actions to perform if the criteria enforced by the match commands are met. The noippolicyroute-map command deletes the pointer to the route map.

Policy routing can be performed on any match criteria that can be defined in an extended IP access list when using thematchipaddresscommand and referencing an extended IP access list.

Related Commands

To establish static routes, use theiproute command in global configuration mode. Toremove static routes, use the noform of this command.

Syntax Description

Command Default

No static routes are established.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

The establishment of a static route is appropriate when the Cisco IOS software cannot dynamically build a route to the destination.

When you specify a DHCP server to assign a static route, the interface type and number and administrative distance may be configured also. In Cisco IOS Release 12.4(1)T and later releases, this keyword is removed.

For Cisco IOS Release 12.4(1)T and later releases, use the global keyword with the vrf vrf-name keyword and argument combination to specify that the next hop address is global.

If you specify an administrative distance, you are flagging a static route that can be overridden by dynamic information. For example, routes derived with Enhanced Interior Gateway Routing Protocol (EIGRP) have a default administrative distance of 100. To have a static route that would be overridden by an EIGRP dynamic route, specify an administrative distance greater than 100. Static routes have a default administrative distance of 1.

Static routes that point to an interface on a connected router will be advertised by way of Routing Information Protocol (RIP) and EIGRP regardless of whether redistributestatic commands are specified for those routing protocols. This situation occurs because static routes that point to an interface are considered in the routing table to be connected and hence lose their static nature. Also, the target of the static route should be included in the network(DHCP) command. If this condition is not met, no dynamic routing protocol will advertise the route unless a redistributestaticcommand is specified for these protocols. With the following configuration:

rtr1 (serial 172.16.188.1/30)--------------> rtr2(Fast Ethernet 172.31.1.1/30) ------>
router [rip | eigrp]
 network 172.16.188.0
 network 172.31.0.0 

• RIP and EIGRP redistribute the route if the route is pointing to the Fast Ethernet interface:

ip route 172.16.188.252 255.255.255.252 FastEthernet 0/0 

RIP and EIGRP do not redistribute the route with the followingiproutecommand because of the split horizon algorithm:

ip route 172.16.188.252 255.255.255.252 serial 2/1 

• EIGRP redistributes the route with both of the following commands:

ip route 172.16.188.252 255.255.255.252 FastEthernet 0/0
ip route 172.16.188.252 255.255.255.252 serial 2/1 

With the Open Shortest Path First (OSPF) protocol, static routes that point to an interface are not advertised unless a redistributestaticcommand is specified.

Adding a static route to an Ethernet or other broadcast interface (for example, ip route 0.0.0.0 0.0.0.0 Ethernet 1/2) will cause the route to be inserted into the routing table only when the interface is up. This configuration is not generally recommended. When the next hop of a static route points to an interface, the router considers each of the hosts within the range of the route to be directly connected through that interface, and therefore it will send Address Resolution Protocol (ARP) requests to any destination addresses that route through the static route.

A logical outgoing interface, for example, a tunnel, needs to be configured for a static route. If this outgoing interface is deleted from the configuration, the static route is removed from the configuration and hence does not show up in the routing table. To have the static route inserted into the routing table again, configure the outgoing interface once again and add the static route to this interface.

The practical implication of configuring the iproute0.0.0.00.0.0.0ethernet1/2 command is that the router will consider all of the destinations that the router does not know how to reach through some other route as directly connected to Ethernet interface 1/2. So the router will send an ARP request for each host for which it receives packets on this network segment. This configuration can cause high processor utilization and a large ARP cache (along with memory allocation failures). Configuring a default route or other static route that directs the router to forward packets for a large range of destinations to a connected broadcast network segment can cause your router to reload.

Specifying a numerical next hop that is on a directly connected interface will prevent the router from using proxy ARP. However, if the interface with the next hop goes down and the numerical next hop can be reached through a recursive route, you may specify both the next hop and interface (for example, ip route 0.0.0.0 0.0.0.0 ethernet 1/2 10.1.2.3) with a static route to prevent routes from passing through an unintended interface.

Note

Configuring a default route that points to an interface, such as iproute0.0.0.00.0.0.0ethernet1/2,displays a warning message. This command causes the router to consider all the destinations that the router cannot reach through an alternate route, as directly connected to Ethernet interface 1/2. Hence, the router sends an ARP request for each host for which it receives packets on this network segment. This configuration can cause high processor utilization and a large ARP cache (along with memory allocation failures). Configuring a default route or other static route that directs the router to forward packets for a large range of destinations to a connected broadcast network segment can cause the router to reload.

The namenext-hop-name keyword and argument combination allows you to associate static routes with names in your running configuration. If you have several static routes, you can specify names that describe the purpose of each static route in order to more easily identify each one.

The tracknumber keyword and argument combination specifies that the static route will be installed only if the state of the configured track object is up.

Recursive Static Routing

In a recursive static route, only the next hop is specified. The output interface is derived from the next hop.

For the following recursive static route example, all destinations with the IP address prefix address prefix 192.168.1.1/32 are reachable via the host with address 10.0.0.2:

ip route 192.168.1.1 255.255.255.255 10.0.0.2

A recursive static route is valid (that is, it is a candidate for insertion in the IPv4 routing table) only when the specified next hop resolves, either directly or indirectly, to a valid IPv4 output interface, provided the route does not self-recurse, and the recursion depth does not exceed the maximum IPv4 forwarding recursion depth.

The following example defines a valid recursive IPv4 static route:

interface serial 2/0
 ip address 10.0.0.1 255.255.255.252
 exit
ip route 192.168.1.1 255.255.255.255 10.0.0.2

The following example defines an invalid recursive IPv4 static route. This static route will not be inserted into the IPv4 routing table because it is self-recursive. The next hop of the static route, 192.168.1.0/30, resolves via the first static route 192.168.1.0/24, which is itself a recursive route (that is, it only specifies a next hop). The next hop of the first route, 192.168.1.0/24, resolves via the directly connected route via the serial interface 2/0. Therefore, the first static route would be used to resolve its own next hop.

interface serial 2/0
 ip address 10.0.0.1 255.255.255.252
 exit
ip route 192.168.1.0 255.255.255.0 10.0.0.2
ip route 192.168.1.0 255.255.255.252 192.168.1.100

It is not normally useful to manually configure a self-recursive static route, although it is not prohibited. However, a recursive static route that has been inserted in the IPv4 routing table may become self-recursive as a result of some transient change in the network learned through a dynamic routing protocol. If this situation occurs, the fact that the static route has become self-recursive will be detected and the static route will be removed from the IPv4 routing table, although not from the configuration. A subsequent network change may cause the static route to no longer be self-recursive, in which case it will be re-inserted in the IPv4 routing table.

Note

IPv4 recursive static routes are checked at one-minute intervals. Therefore, a recursive static route may take up to a minute to be inserted into the routing table once its next hop becomes valid. Likewise, it may take a minute or so for the route to disappear from the table if its next hop becomes invalid.

Related Commands

To enable IP routing table statistics collection, use the iprouteprofile command in global configuration mode. To disable collection of routing table statistics, use the no form of the command.

Syntax Description

This command has no arguments or keywords.

Command Default

The time interval for each sample, or sampling interval, is a fixed value and is set at 5 seconds.

Command Modes

Global configuration

Command History

Usage Guidelines

The iprouteprofile command helps you to monitor routing table fluctuations that can occur as the result of route flapping, network failure, or network restoration.

This command identifies route flapping over brief time intervals. The time interval for each sample, or sampling interval, is a fixed value and is set at 5 seconds.

Two sets of statistics are collected. The per-interval statistics are collected over a sampling interval, while the routing table change statistics are the result of aggregating the per-interval statistics. The per-interval statistics are collected as a single set of counters, with one counter tracking one event. All counters are initialized at the beginning of each sampling interval; counters are incremented as corresponding events occur anywhere in the routing table.

At the end of a sampling interval, the per-interval statistics for that sampling interval are integrated with the routing table change statistics collected from the previous sampling intervals. The counters holding the per-interval statistics are reset and the process is repeated.

Routing table statistics are collected for the following events:

• Forward-Path Change. This statistic is the number of changes in the forwarding path, which is the accumulation of prefix-add, next-hop change, and pathcount change statistics.
• Prefix-Add. A new prefix was added to the routing table.
• Next-Hop Change. A prefix is not added or removed, but the next hop changes. This statistic is only seen with recursive routes that are installed in the routing table.
• Pathcount Change. The number of paths in the routing table has changed. This statistic is the result of an increase in the number of paths for an Interior Gateway Protocol (IGP) prefix in the routing table.
• Prefix Refresh. Standard routing table maintenance; the forwarding behavior is not changed.

Use the showiprouteprofile command to display the routing table change statistics.

Related Commands

To ch ange the time interval for IP static route adjustments during convergence, use the iproutestaticadjust-timecommand in global configuration mode. To reinstate the default adjustment time of 60 seconds, use the no form of this command.

Syntax Description

Command Default

seconds : 60

Command Modes

Global configuration

Command History

Usage Guidelines

By default, static route adjustments are made every 60 seconds. To adjust the timer to any interval from 1 to 60 seconds, enter the ip route static adjust-time command.

The benefit of reducing the timer from the 60-second default value is to increase the convergence when static routes are used. However, reducing the interval can be CPU intensive if the value is set very low and a large number of static routes are configured.

Related Commands

To specify static route Bidirectional Forwarding Detection (BFD) neighbors, use the iproutestaticbfdcommand in global configuration mode. To remove a static route BFD neighbor, use the noform of this command.

Syntax Description

Command Default

No static BFD neighbors are specified.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

Use the ip route static bfd command to specify static route BFD neighbors. All static routes that have the same interface and gateway specified in the configuration share the same BFD session for reachability notification.

All static routes that specify the same values for the interface-type, interface-number, and ip-addressarguments will automatically use BFD to determine gateway reachability and take advantage of fast failure detection.

The interface-type, interface-number, and ip-address arguments are required because BFD supports only directly connected neighbors for the Cisco IOS 12.2(33)SRC, 15.1(2)S, and 15.1(2)SNG releases.

The group keyword assigns a BFD group. The static BFD configuration is added to the VPN routing and forwarding (VRF) instance with which the interface is associated. The passive keyword specifies the passive member of the group. Adding a static BFD in a group without the passive keyword makes it an active member of the group. A static route should be tracked by the active BFD configuration in order to trigger a BFD session for the group. To remove all the static BFD configurations (active and passive) of a specific group, use the noiproutestaticbfd command and specify the BFD group name.

BFD requires that BFD sessions are initiated on both endpoint routers. Therefore, this command must be configured on each endpoint router.

The BFD static session on a switch virtual interface (SVI) gets established only after disabling and enabling the bfd interval milliseconds min_rx milliseconds multiplier multiplier-value command on that SVI.

To enable the static BFD sessions, complete the following steps:

1. Enable BFD timers on the SVI.

   bfd interval milliseconds min_rx milliseconds multiplier multiplier-value

2. Enable BFD for static IP route.

   ip route static bfd interface-type interface-number ip-address

3. Disable and enable the BFD timers on the SVI again.

   no bfd interval milliseconds min_rx milliseconds multiplier multiplier-value

   bfd interval milliseconds min_rx milliseconds multiplier multiplier-value

Related Commands

To enable IP routing, use the ip routing command in global configuration mode. To disable IP routing, use the noform of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

IP routing is enabled.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

To bridge IP, the no ip routing command must be configured to disable IP routing. However, you need not specify no ip routing in conjunction with concurrent routing and bridging to bridge IP.

The ip routing command is disabled on the Cisco VG200 voice over IP gateway.

Disabling IP routing is not allowed if you are running Cisco IOS Release 12.2SX on a Catalyst 6000 platform. The workaround is to not assign an IP address to the SVI.

To purge the routes of the routing protocols when an interface goes down, use the iproutingprotocolpurgeinterface command in global configuration mode. To disable the purging of the routes, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

Routing protocols purge the routes by default when an interface goes down.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

The iproutingprotocolpurgeinterface command allows the Routing Information Base (RIB) to ignore interface events for protocols that can respond to interface failures, thus eliminating any unnecessary deletion by the RIB. This in turn results in a single modify event to the Cisco Express Forwarding plane.

If the noiproutingprotocolpurgeinterface command is executed and a link goes down, the RIB process is automatically triggered to delete all prefixes that have the next hop on this interface from the RIB. The protocols on all the routers are notified, and if there is a secondary path, the protocols will update the RIB with the new path. When the process works through a large routing table, the process can consume many CPU cycles and increase the convergence time.

To enable local policy-based routing (PBR) for IPv6 packets, use the ipv6 local policy route-map command in global configuration mode. To disable local policy-based routing for IPv6 packets, use the no form of this command.

Syntax Description

Command Default

IPv6 packets are not policy routed.

Command Modes

Global configuration (config#)

Command History

Usage Guidelines

Packets originating from a router are not normally policy routed. However, you can use the ipv6 local policy route-map command to policy route such packets. You might enable local PBR if you want packets originated at the router to take a route other than the obvious shortest path.

The ipv6 local policy route-map command identifies a route map to be used for local PBR. The route-map commands each have a list of match and set commands associated with them. The match commands specify the match criteria, which are the conditions under which packets should be policy routed. The set commands specify set actions, which are particular policy routing actions to be performed if the criteria enforced by the match commands are met. The no ipv6 local policy route-map command deletes the reference to the route map and disables local policy routing.

Related Commands

To configure IPv6 policy-based routing (PBR) on an interface, use the ipv6 policy route-map command in interface configuration mode. To disable IPv6 PBR on an interface, use the no form of this command.

Syntax Description

Command Default

Policy-based routing does not occur on the interface.

Command Modes

Interface configuration (config-if)

Command History

Usage Guidelines

You can enable PBR if you want your packets to take a route other than the obvious shortest path.

The ipv6 policy route-map command identifies a route map to be used for policy-based routing. The route-map commands each have a list of match and set commands associated with them. The match commands specify the match criteria, which are the conditions under which PBR is allowed for the interface. The set commands specify set actions, which are the PBR actions to be performed if the criteria enforced by the match commands are met. The no ipv6 policy route-map command deletes the pointer to the route map.

Policy-based routing can be performed on any match criteria that can be defined in an IPv6 access list.

Related Commands

To specify static route Bidirectional Forwarding Detection for IPv6 (BFDv6) neighbors, use the ipv6 route static bfd command in global configuration mode. To remove a static route BFD neighbor, use the no form of this command.

Syntax Description

Command Default

No static BFDv6 neighbors are specified.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

Use the ipv6 route static bfd command to specify static route neighbors. All static routes that have the same interface and gateway specified in the configuration share the same BFDv6 session for reachability notification. BFDv6 requires that BFDv6 sessions are initiated on both endpoint routers. Therefore, this command must be configured on each endpoint router. An IPv6 static BFDv6 neighbor must be fully specified (with the interface and the neighbor address) and must be directly attached.

All static routes that specify the same values for vrfvrf-name , interface-type interface-number , and ipv6-address will automatically use BFDv6 to determine gateway reachability and take advantage of fast failure detection.

Related Commands

To allow a recursive IPv6 static route to resolve using the default IPv6 static route, use the ipv6 route static resolve defaultcommand in global configuration mode. To remove this function, use the no form of this command.

Syntax Description

This command has no arguments or keywords.

Command Default

Recursive IPv6 static routes do not resolve via the default route.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

By default, a recursive IPv6 static route will not resolve using the default route (::/0). The ipv6 route static resolve default command restores legacy behavior and allows resolution using the default route.

To identify an authentication key on a key chain, use the key command in key-chain configuration mode. To remove the key from the key chain, use the no form of this command.

Syntax Description

Command Default

No key exists on the key chain.

Command Modes

Key-chain configuration (config-keychain)

Command History

Usage Guidelines

Only DRP Agent, Enhanced Interior Gateway Routing Protocol (EIGRP), and Routing Information Protocol (RIP) Version 2 use key chains.

It is useful to have multiple keys on a key chain so that the software can sequence through the keys as they become invalid after time, based on the accept-lifetime and send-lifetime key chain key command settings.

Each key has its own key identifier, which is stored locally. The combination of the key identifier and the interface associated with the message uniquely identifies the authentication algorithm and Message Digest 5 (MD5) authentication key in use. Only one authentication packet is sent, regardless of the number of valid keys. The software starts looking at the lowest key identifier number and uses the first valid key.

If the last key expires, authentication will continue and an error message will be generated. To disable authentication, you must manually delete the last valid key.

To remove all keys, remove the key chain by using the no key chain command.

Related Commands

To define an authentication key chain needed to enable authentication for routing protocols and enter key-chain configuration mode, use the key chain command in global configuration mode. To remove the key chain, use the no form of this command.

Syntax Description

Command Default

No key chain exists.

Command Modes

Global configuration (config)

Command History

Usage Guidelines

Only DRP Agent, Enhanced Interior Gateway Routing Protocol (EIGRP), and Routing Information Protocol (RIP) Version 2 use key chains.

You must configure a key chain with keys to enable authentication.

Although you can identify multiple key chains, we recommend using one key chain per interface per routing protocol. Upon specifying the key chain command, you enter key chain configuration mode.

Related Commands

To specify the authentication string for a key, use the key-string(authentication) command in key chain key configuration mode. To remove the authentication string, use the no form of this command.

Syntax Description

Command Default

No authentication string for a key exists.

Command Modes

Key chain key configuration (config-keychain-key)

Command History

Usage Guidelines

Only DRP Agent, Enhanced Interior Gateway Routing Protocol (EIGRP), and Routing Information Protocol ( RIP) Version 2 use key chains. Each key can have only one key string.

If password encryption is configured (with the service password-encryption command), the software saves the key string as encrypted text. When you write to the terminal with the more system:running-config command, the software displays key-string 7 encrypted text.

Related Commands

To distribute any routes that have their next hop out one of the interfaces specified, use the matchinterface command in route-map configuration mode. To remove the matchinterface entry, use the no form of this command.