Configuration Prerequisites; Configuration Guidelines; Configuration Procedure - HP FlexFabric 12900E Series Configuration Manual

In Figure 41, after you enable FRR on Router B, IS-IS automatically calculates or designates a
backup next hop when a link failure is detected. In this way, packets are directed to the backup next
hop to reduce traffic recovery time. Meanwhile, IS-IS calculates the shortest path based on the new
network topology, and forwards packets over the path after network convergence.
You can assign a backup next hop for IS-IS FRR through the following ways:
•
Enable IS-IS FRR to calculate a backup next hop through Loop Free Alternate (LFA)
calculation.
•
Designate a backup next hop with a routing policy for routes matching specific criteria.

Configuration prerequisites

Before you configure IS-IS FRR, complete the following tasks:
•
Configure IP addresses for interfaces to ensure IP connectivity between neighboring nodes.
•
Enable IS-IS.

Configuration guidelines

The LFA calculation of FRR and that of TE are mutually exclusive.

Configuration procedure

Configuring IS-IS FRR to calculate a backup next hop through LFA calculation
Step
1. Enter system view.
2. Enter interface view.
3. (Optional.) Disable LFA
calculation
interface.
4. Return to system view.
5. Enter IS-IS IPv4 unicast
address family view.
6. Enable
calculate a backup next
hop
calculation.
Configuring IS-IS FRR using a routing policy
You can use the apply fast-reroute backup-interface command to specify a backup next hop in a
routing policy for routes matching specific criteria. You can also perform this task to reference the
routing policy for IS-IS FRR. For more information about the apply fast-reroute backup-interface
command and routing policy configurations, see
To configure IS-IS FRR using a routing policy:
Command
system-view
interface interface-type interface-number
on the
isis fast-reroute lfa-backup exclude
quit
a
b
c
IS-IS FRR to
fast-reroute lfa
through LFA
isis [ process-id ]
vpn-instance-name ]
cost-style { wide | wide-compatible }
address-family ipv4 [ unicast ]
"Configuring routing
162
Remarks
N/A
N/A
By default, the interface
participates
calculation, and can be
elected as a backup
interface.
N/A
[ vpn-instance
N/A
By default, IS-IS FRR is
disabled.
policies."
in LFA