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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
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