Description

This document helps to configure higher preference for SR (segment routing) over LDP.

Symptoms

Topology:

 

R1(1.1.1.1) --------ISIS,SR,LDP------------R3(3.3.3.3)

 

R1 is learning R3's loopback 3.3.3.3 via SR as well as LDP.

 

By default, LDP route is preferred.

 

inet.0: 22 destinations, 22 routes (22 active, 0 holddown, 0 hidden)

+ = Active Route, - = Last Active, * = Both

 

3.3.3.3/32        *[IS-IS/18] 00:12:33, metric 10

                    > to 20.20.20.2 via ge-0/0/1.0

 

inet.3: 5 destinations, 8 routes (5 active, 0 holddown, 0 hidden)

+ = Active Route, - = Last Active, * = Both

 

3.3.3.3/32        *[LDP/9] 00:07:35, metric 1

                   > to 20.20.20.2 via ge-0/0/1.0

                    [L-ISIS/14] 00:04:16, metric 10

                   > to 20.20.20.2 via ge-0/0/1.0, Push 0

 

Solution

Add below configuration to get SR route preferred over LDP:

set protocols isis level 1 labeled-preference 8

 

 

After adding above config:

inet.0: 22 destinations, 22 routes (22 active, 0 holddown, 0 hidden)

+ = Active Route, - = Last Active, * = Both

 

3.3.3.3/32     *[IS-IS/18] 00:00:08, metric 10

          > to 20.20.20.2 via ge-0/0/1.0

 

inet.3: 5 destinations, 8 routes (5 active, 0 holddown, 0 hidden)

+ = Active Route, - = Last Active, * = Both

 

3.3.3.3/32     *[L-ISIS/8] 00:00:08, metric 10

          > to 20.20.20.2 via ge-0/0/1.0, Push 0

          [LDP/9] 00:00:08, metric 1

          > to 20.20.20.2 via ge-0/0/1.0

 

 

 

 

Modification History

2024-07-31 : Article Created