思科路由器BFD配置命令详解

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

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

[

passi

ve

]]

8.

ip

route

[

vrf

vrf- name

]

prefix

mask

{

ip- address

|

interface- type

interface- number

[

ip- addr

ess

]} [

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 Action

Purpose

Ste

enable

p 1

Example:

Enables privileged EXEC

mode.

?

Device> enable

Ste

configure

terminal

p 2

Enter your

password if

prompted.

Enters global

configuration mode.

Example:

Device# configure terminal

Ste

interface

type

number

p 3

Example:

Configures an interface

and enters interface

configuration mode.

Device(config)# interface serial 2/0

Ste

ip

address

ip- address

mask

p 4

Example:

Configures an IP address

for the interface.

Device(config-if)# ip address

10.201.201.1 255.255.255.0

Ste

bfd

interval

milliseconds

min_rx

milliseconds

multi

Enables BFD on the

p 5

plier

interval- multiplier

interface.

Example:

Device(config-if)# bfd interval 500

min_rx 500 multiplier 5

Ste

exit

p 6

Example:

Exits interface

configuration mode and

returns to global

configuration mode.

Device(config-if)# exit

Ste

ip

route

static

bfd

interface- type

interface- number

i

Specifies a static route

p 7

p-address

[

group

group- name

[

passive

]]

BFD neighbor.

?

The

interface- type

,

i

nterface-number

,

Example:

Device(config)# ip route static bfd

serial 2/0 10.1.1.1 group group1

and

ip- address

arg

uments are

required because