tiebreaker preference

Function

The tiebreaker command sets the solution of selecting a backup path for OSPF IP FRR.

The undo tiebreaker command restores the default solution of selecting a backup path for OSPF IP FRR.

By default, the solution of selecting a backup path for OSPF IP FRR is node-protection path first.

Format

tiebreaker { node-protecting | lowest-cost | ldp-sync hold-max-cost | srlg-disjoint } preference value

undo tiebreaker { node-protecting | lowest-cost | ldp-sync hold-max-cost | srlg-disjoint } [ preference value ]

Parameters

Parameter	Description	Value
node-protecting	Sets the solution of selecting a backup path for OSPF IP FRR to node-protection path first.	-
lowest-cost	Sets the solution of selecting a backup path for OSPF IP FRR to smallest-cost path first.	-
ldp-sync	Sets the solution of selecting a backup path for OSPF IP FRR to LDP-IGP synchronization-capable path first.	-
hold-max-cost	Sets the solution of selecting a backup path for OSPF IP FRR to maximum-cost (set by LDP-IGP synchronization) path first.	-
srlg-disjoint	Sets the solution of selecting a backup path for OSPF IP FRR to shared risk link group (SRLG) disjoint first.	-
preference value	Specifies a priority for the solution. The larger the value, the higher the priority.	The value is an integer ranging from 1 to 255. By default, the priority of the node-protection path first solution is 40, the priority of the smallest-cost path first solution is 20, the priority of the maximum-cost (set by LDP-IGP synchronization) path first solution is 10, and the priority of SRLG disjoint path first solution is 5.

Views

OSPF FRR view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
ospf	write

Usage Guidelines

Usage Scenario

In an inter-board scenario, as shown in Figure 2 in "Enabling OSPF IP FRR" in the Configuration Guide, the path from Device A to Device D is the primary path and the path from Device D to Link-1,Device A-> Device E-> Device D(Link-2) is the backup path. When the primary path Link-1 fails, the primary link is switched to Link-2, and the backup path is Device A-> Device B-> Device C-> Device D(Link-3). After Link-1 goes Up, OSPF enters the Hold max cost state because the LDP session is not Up. The primary link is still Link-2, and the backup link is Link-3. After the LDP session goes Up, if ldp-sync hold-max-cost is not configured, OSPF exits the Hold max cost state after the LDP advertisement Up timer expires. IGP switches the primary path back to Link-1. Because the upstream and downstream entries are on different boards, packet loss occurs on different boards if the downstream entries are not updated. To address this problem, configure the ldp-sync hold-max-cost,OSPF to preferentially select the path with the maximum cost advertised by LDP when the ldp-sync hold-max-cost,OSPF is in the Hold max cost state. The backup path is switched to Link-1, and the backup forwarding entry is delivered in advance. After the timer for LDP to advertise the Up state expires, OSPF exits the Hold max cost state and switches the link back to the primary path Link-1. In this case, backup entries exist in the downstream table, preventing inter-board packet loss.

Prerequisites

The OSPF FRR view has been displayed using the frr command, and OSPF IP FRR has been enabled using the loop-free-alternate command.

Precautions

If ldp-sync hold-max-cost is configured, you need to run the maximum-link-cost command to change the maximum link cost to a value smaller than 65535.

Example

# Set the solution of selecting a backup path for OSPF IP FRR to smallest-cost path first.

<HUAWEI> system-view
[~HUAWEI] ospf 1
[*HUAWEI-ospf-1] frr
[*HUAWEI-ospf-1-frr] loop-free-alternate
[*HUAWEI-ospf-1-frr] tiebreaker lowest-cost preference 255