BFD Multihop Support for IPv4 Static Routes

The BFD Multihop Support for IPv4 Static Routes feature enables detection of IPv4 network failure between paths that are not directly connected. If a Bidirectional Forwarding Detection (BFD) session is up (that is, the next-hop destination is reachable), IPv4 static routes that are associated with IPv4 static BFD configuration are added to a routing table. If the BFD session is down, the routing table removes all associated static routes from the routing table.

This feature is applicable on different kinds of interfaces such as physical, subinterface, and virtual tunnels and across intra-area and interarea topologies.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.

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Prerequisites for BFD Multihop Support for IPv4 Static Routes

  • The BFD destination for which an IPv4 static route has to be configured must be reachable by all devices.
  • The configured device must have at least one static route with the next-hop destination as a BFD destination for an associated session. If not, the BFD session is not created on the device.

Information About BFD Multihop Support for IPv4 Static Routes

BFDv4 Associated Mode

In Bidirectional Forwarding Detection for IPv4 (BFDv4) associated mode, an IPv4 static route is automatically associated with an IPv4 static BFDv4 multihop destination address if the static route next hop exactly matches the static BFDv4 multihop destination address.

The state of the BFDv4 session is used to determine whether the associated IPv4 static routes are added in the IPv4 routing information base (RIB). For example, static routes are added in the IPv4 RIB only if the BFDv4 multihop destination is reachable, and the static routes are removed from the IPv4 RIB if the BFDv4 multihop destination subsequently becomes unreachable.

BFDv4 Unassociated Mode

In Bidirectional Forwarding Detection for IPv4 (BFDv4), an IPv4 static BFD multihop destination can be configured in unassociated mode. In unassociate mode, a BFD neighbor is not associated with a static route, and the BFD sessions are requested if the IPv4 static BFD is configured.

Unassociated mode is useful in the following scenario:

  • Absence of an IPv4 static route—This scenario occurs when a static route is on device A, and device B is the next hop. In associated mode, you must create both a static BFD multihop destination address and a static route on both devices to bring up the BFDv4 session from device B to device A. Specifying the static BFD multihop destination in unassociated mode on device B avoids the need to configure an unwanted static route.

How to Configure BFD Multihop Support for IPv4 Static Routes

Configuring BFD Multihop IPv4 Static Routes

Before you begin

  • Specify a BFD destination address which is same as the IPv4 static route next hop or gateway address.
  • Configure a BFD map and a BFD multihop template for an interface on the device. The destination address and source address configured for a BFD map must match the BFD static multihop configuration and the source address must be a valid IP address configured for an interface in the routing table.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. ip route prefix mask ip-address
  4. ip route static bfd multihop-destination-address multihop-source-address
  5. ip route static bfd multihop-destination-address multihop-source-address unassociate
  6. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:

Device> enable
Enables privileged EXEC mode.
  • Enter your password if prompted.
Step 2

configure terminal

Example:

Device# configure terminal

Enters global configuration mode.

Step 3

ip route prefix mask ip-address

Example:

Device(config)# ip route 192.0.2.0 255.255.255.0 10.1.1.2

Configures an IPv4 static route that BFD multihop uses to monitor static routes.

Step 4

ip route static bfd multihop-destination-address multihop-source-address

Example:

Device(config)# ip route static bfd 192.0.2.1 10.1.1.1

Configures the static IPv4 BFD multihop to be associated with a static IPv4 route.

Step 5

ip route static bfd multihop-destination-address multihop-source-address unassociate

Example:

Device(config)# ip route static bfd 192.0.2.1 10.1.1.1 unassociate

(Optional) Configures the static IPv4 BFD multihop to be associated with a static IPv4 route in unassociated mode.

Step 6

end

Example:

Device(config)# end

Exits global configuration mode and returns to privileged EXEC mode.

Verifying BFD Multihop Support for IPv4 Static Routes

The following show commands can be used to verify IPv4 static routes for BFD multihop:

SUMMARY STEPS

  1. show bfd neighbor
  2. show ip static route bfd

DETAILED STEPS

Step 1

show bfd neighbor

Displays a line-by-line listing of existing BFD adjacencies.

Step 2

show ip static route bfd

Displays information about the IPv4 static BFD configured parameters.

Configuration Examples for BFD Multihop Support for IPv4 Static Routes

Example: Configuring BFD Multihop for IPv4 Static Routes in Associated Mode

Device> enable
Device# configure terminal
Device(config)# bfd map ipv4 192.0.2.1/32  10.1.1.1/32 test         
Device(config)# bfd-template multi-hop test
Device(config-bfd)# interval min-tx 51 min-rx 51 multiplier 3
Device(config-bfd)# exit
Device(config)# ip route 192.0.2.0 255.255.255.0 10.1.1.2
Device(config)# interface GigabitEthernet 1/1
Device(config-if)# ip address 10.1.1.1 255.255.0.0
Device(config-if)# exit
Device(config)# ip route static bfd 192.0.2.1 10.1.1.1
Device(config)# end

Example: Configuring IPv4 Static Multihop for BFD in Unassociated Mode

Device> enable
Device# configure terminal
Device(config)# bfd map ipv4 192.0.2.1/32  10.1.1.1/32 test         
Device(config)# bfd-template multi-hop test
Device(config-bfd)# interval min-tx 51 min-rx 51 multiplier 3
Device(config-bfd)# exit
Device(config)# ip route 192.0.2.0 255.255.255.0 10.1.1.2
Device(config)# interface GigabitEthernet 1/1
Device(config-if)# ip address 10.1.1.1 255.255.0.0
Device(config-if)# exit
Device(config)# ip route static bfd 192.0.2.1 10.1.1.1 unassociate
Device(config)# end

Additional References for BFD Multihop Support for IPv4 Static Routes

Related Documents

Related Topic Document Title

Cisco IOS commands

Cisco IOS Master Command List, All Releases

IP Routing: Protocol Independent commands

IP Routing Protocol-Independent Command Reference

Standards and RFCs

Standard/RFC Title
RFC 5883 BFD for Multihop Paths

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Feature Information for BFD Multihop Support for IPv4 Static Routes

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1. Feature Information for BFD Multihop Support for IPv4 Static Routes

Feature Name

Releases

Feature Information

BFD Multihop Support for IPv4 Static Routes

Cisco IOS XE Release 3.9S

The BFD Multihop Support for IPv4 Static Routes feature enables detection of IPv4 network failure between paths that are not directly connected. If a Bidirectional Forwarding Detection (BFD) session is up (that is, the next-hop destination is reachable), IPv4 static routes that are associated with IPv4 static BFD configuration are added to a routing table. If the BFD session is down, the routing table removes all associated static routes from the routing table.

The following commands were modified: ip route static bfd and show ip static route bfd .