Bfd Operation - Nokia 7705 SAR-W Series Manual

Label Distribution Protocol
Given the above behavior, it is recommended that the user configures the sync timer
to a value which allows enough time for both the LDP IPv4 and LDP IPv6 sessions
to come up.

5.4.8 BFD Operation

The operation of BFD over an LDP interface tracks the next hop of prefix IPv4 and
prefix IPv6 in addition to tracking of the LDP peer address of the Hello adjacency
over that link. Tracking is required because LDP can resolve both IPv4 and IPv6
prefix FECs over a single IPv4 or IPv6 LDP session and therefore, the next hop of a
prefix will not necessarily match the LDP peer source address of the Hello adjacency.
If any of the BFD tracking sessions fail, the LFA backup NHLFE for the FEC is
activated, or, if there is no FRR backup, the FEC is re-resolved.
The user can configure tracking with only an IPv4 BFD session, only an IPv6 BFD
session, or with both using the config>router>ldp>if-params>if>bfd-enable [ipv4]
[ipv6] command.
This command provides flexibility in case the user does not need to track both Hello
adjacency and the next hops of FECs.
For example, if the user configures bfd-enable ipv6 only to save on the number of
BFD sessions, then LDP will track the IPv6 Hello adjacency and the next hops of IPv6
prefix FECs. LDP will not track next hops of IPv4 prefix FECs resolved over the same
LDP IPv6 adjacency. If the IPv4 data plane encounters errors and the IPv6 Hello
adjacency is not affected and remains up, traffic for the IPv4 prefix FECs resolved
over that IPv6 adjacency will be blackholed. If the BFD tracking the IPv6 Hello
adjacency times out, then all IPv4 and IPv6 prefix FECs will be updated.
420
• If the router interface is up and only one of the LDP IPv4 or LDP IPv6 interfaces
goes down, no action is taken.
• When the router interface comes up from a down state, and the LDP IPv4 or LDP
IPv6 sessions comes up, IGP starts the sync timer. When the sync timer expires,
the interface metric is restored to its configured value and all static routes with
the ldp-sync option enabled are activated.
Use subject to Terms available at: www.nokia.com
© 2022 Nokia.
MPLS Guide
3HE 18686 AAAB TQZZA