BFD - Static Route Support

The BFD - Static Route Support feature enables association of static routes with a static Bidirectional Forwarding Detection (BFD) configuration in order to monitor static route reachability using the configured BFD session. Depending on status of the BFD session, static routes are added to or removed from the Routing Information Base (RIB).

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Prerequisites for BFD - Static Route Support

  • Cisco Express Forwarding and IP routing must be enabled on all participating routers.

  • The baseline parameters for Bidirectional Forwarding Detection (BFD) sessions on the interfaces over which you want to run BFD sessions to BFD neighbors must be configured.

Restrictions for BFD - Static Route Support

  • The Cisco IOS software incorrectly allows configuration of BFD on virtual-template and dialer interfaces; however, BFD functionality on virtual-template and dialer interfaces is not supported. Avoid configuring BFD on virtual-template and dialer interfaces.

  • BFD works only for directly connected neighbors. BFD neighbors must be no more than one IP hop away. Multihop configurations are not supported.

  • BFD support is not available for all platforms and interfaces. To confirm BFD support for a specific platform or interface and obtain the most accurate platform and hardware restrictions, see the Cisco IOS software release notes for your software version.

Information About BFD - Static Route Support

Overview of BFD - Static Route Support

The BFD - Static Route Support feature enables association of static routes with a static Bidirectional Forwarding Detection (BFD) configuration in order to monitor static route reachability using the configured BFD session. Depending on status of the BFD session, static routes are added to or removed from the Routing Information Base (RIB).

Unlike dynamic routing protocols, such as OSPF and BGP, static routing has no method of peer discovery. Therefore, when BFD is configured, the reachability of the gateway is completely dependent on the state of the BFD session to the specified neighbor. Unless the BFD session is up, the gateway for the static route is considered unreachable, and therefore the affected routes will not be installed in the appropriate RIB.

For a BFD session to be successfully established, BFD must be configured on the interface on the peer and there must be a BFD client registered on the peer for the address of the BFD neighbor. When an interface is used by dynamic routing protocols, the latter requirement is usually met by configuring the routing protocol instances on each neighbor for BFD. When an interface is used exclusively for static routing, this requirement must be met by configuring static routes on the peers.

If a BFD configuration is removed from the remote peer while the BFD session is in the up state, the updated state of the BFD session is not signaled to IPv4 static. This will cause the static route to remain in the RIB. The only workaround is to remove the IPv4 static BFD neighbor configuration so that the static route no longer tracks BFD session state. Also, if you change the encapsulation type on a serial interface to one that is unsupported by BFD, BFD will be in a down state on that interface. The workaround is to shut down the interface, change to a supported encapsulation type, and then reconfigure BFD.

A single BFD session can be used by an IPv4 static client to track the reachability of next hops through a specific interface. You can assign a BFD group for a set of BFD-tracked static routes. Each group must have one active static BFD configuration, one or more passive BFD configurations, and the corresponding static routes to be BFD-tracked. Nongroup entries are BFD-tracked static routes for which a BFD group is not assigned. A BFD group must accommodate static BFD configurations that can be part of different VRFs. Effectively, the passive static BFD configurations need not be in the same VRF as that of the active configuration.

For each BFD group, there can be only one active static BFD session. You can configure the active BFD session by adding a static BFD configuration and a corresponding static route that uses the BFD configuration. The BFD session in a group is created only when there is an active static BFD configuration and the static route that uses the static BFD configuration. When the active static BFD configuration or the active static route is removed from a BFD group, all the passive static routes are withdrawn from the RIB. Effectively, all the passive static routes are inactive until an active static BFD configuration and a static route to be tracked by the active BFD session are configured in the group.

Similarly, for each BFD group, there can be one or more passive static BFD configurations and their corresponding static routes to be BFD-tracked. Passive static session routes take effect only when the active BFD session state is reachable. Though the active BFD session state of the group is reachable, the passive static route is added to the RIB only if the corresponding interface state is up. When a passive BFD session is removed from a group, it will not affect the active BFD session if one existed, or the BFD group reachability status.

How to Configure BFD - Static Route Support

Configuring BFD - Static Route Support

Perform this task to configure BFD support for static routing. Repeat the steps in this procedure on each BFD neighbor. For more information, see the “Example: Configuring BFD Support for Static Routing” section.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface type number

    4.    ip address ip-address mask

    5.    bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier

    6.    exit

    7.    ip route static bfd interface-type interface-number ip-address [group group-name [passive]]

    8.    ip route [vrf vrf-name] prefix mask {ip-address | interface-type interface-number [ip-address]} [dhcp] [distance] [name next-hop-name] [permanent | track number] [tag tag]

    9.    exit

    10.    show ip static route

    11.    show ip static route bfd


DETAILED STEPS
 Command or ActionPurpose
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 interface type number


Example: 
Device(config)# interface serial 2/0
 

Configures an interface and enters interface configuration mode.

 
Step 4 ip address ip-address mask


Example: 
Device(config-if)# ip address 10.201.201.1 255.255.255.0
 

Configures an IP address for the interface.

 
Step 5 bfd interval milliseconds min_rx milliseconds multiplier interval-multiplier


Example: 
Device(config-if)# bfd interval 500 min_rx 500 multiplier 5
 

Enables BFD on the interface.

 
Step 6 exit


Example: 
Device(config-if)# exit
 

Exits interface configuration mode and returns to global configuration mode.

 
Step 7 ip route static bfd interface-type interface-number ip-address [group group-name [passive]]


Example: 
Device(config)# ip route static bfd serial 2/0 10.1.1.1 group group1 passive
 

Specifies a static route BFD neighbor.

  • The interface-type, interface-number, and ip-address arguments are required because BFD support exists only for directly connected neighbors.

 
Step 8 ip route [vrf vrf-name] prefix mask {ip-address | interface-type interface-number [ip-address]} [dhcp] [distance] [name next-hop-name] [permanent | track number] [tag tag]


Example: 
Device(config)# ip route 10.0.0.0 255.0.0.0
 

Specifies a static route BFD neighbor.

 
Step 9 exit


Example: 
Device(config)# exit
 

Exits global configuration mode and returns to privileged EXEC mode.

 
Step 10 show ip static route


Example: 
Device# show ip static route
 

(Optional) Displays static route database information.

 
Step 11 show ip static route bfd


Example: 
Device# show ip static route bfd
 

(Optional) Displays information about the static BFD configuration from the configured BFD groups and nongroup entries.

 

Configuration Examples for BFD - Static Route Support

Example: Configuring BFD - Static Route Support

In the following example, the network consists of Device A and Device B. Serial interface 2/0 on Device A is connected to the same network as serial interface 2/0 on Device B. In order for the BFD session to come up, Device B must be configured.

Device A

configure terminal
interface Serial 2/0
ip address 10.201.201.1 255.255.255.0
bfd interval 500 min_rx 500 multiplier 5
ip route static bfd Serial 2/0 10.201.201.2
ip route 10.0.0.0 255.0.0.0 Serial 2/0 10.201.201.2

Device B

configure terminal
interface Serial 2/0
ip address 10.201.201.2 255.255.255.0
bfd interval 500 min_rx 500 multiplier 5
ip route static bfd Serial 2/0 10.201.201.1
ip route 10.1.1.1 255.255.255.255 Serial 2/0 10.201.201.1

Note that the static route on Device B exists solely to enable the BFD session between 10.201.201.1 and 10.201.201.2. If there is no useful static route that needs to be configured, select a prefix that will not affect packet forwarding, for example, the address of a locally configured loopback interface.

In the following example, there is an active static BFD configuration to reach 209.165.200.225 through Ethernet interface 0/0 in the BFD group testgroup. As soon as the static route is configured that is tracked by the configured static BFD, a single hop BFD session is initiated to 209.165.200.225 through Ethernet interface 0/0. The prefix 10.0.0.0/8 is added to the RIB if a BFD session is successfully established. 

configure terminal
ip route static bfd Ethernet 0/0 209.165.200.225 group testgroup
ip route 10.0.0.0 255.255.255.224 Ethernet 0/0 209.165.200.225

In the following example, a BFD session to 209.165.200.226 through Ethernet interface 0/0.1001 is marked to use the group testgroup. That is, this configuration is a passive static BFD. Though there are static routes to be tracked by the second static BFD configuration, a BFD session is not triggered for 209.165.200.226 through Ethernet interface 0/0.1001. The existence of the prefixes 10.1.1.1/8 and 10.2.2.2/8 is controlled by the active static BFD session (Ethernet interface 0/0 209.165.200.225). 

configure terminal
ip route static bfd Ethernet 0/0 209.165.200.225 group testgroup
ip route 10.0.0.0 255.255.255.224 Ethernet 0/0 209.165.200.225
ip route static bfd Ethernet 0/0.1001 209.165.200.226 group testgroup passive
ip route 10.1.1.1 255.255.255.224 Ethernet 0/0.1001 209.165.200.226
ip route 10.2.2.2 255.255.255.224 Ethernet 0/0.1001 209.165.200.226

Additional References for BFD - Static Route Support

Related Documents

Related Topic Document Title

BFD Commands

IP Routing Protocol-Independent Commands A through R

IP Routing Protocol-Independent Commands S through T

Cisco IOS Commands

Cisco IOS Master Command List, All Releases

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Feature Information for BFD - Static Route Support

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 - Static Route Support

Feature Name

Releases

Feature Information

BFD - Static Route Support

15.2(1)E

The BFD - Static Route Support feature enables association of static routes with a static Bidirectional Forwarding Detection (BFD) configuration in order to monitor static route reachability using the configured BFD session. Depending on status of the BFD session, static routes are added to or removed from the Routing Information Base (RIB).