Description

This Article explains a scenario and solution where if a Static route points to a BGP ECMP INH, then the static route does not inherit the ECMP behaviour of its ECMP NH.

 

Symptoms

Static route riding over a BGP INH (BGP INH is ECMP) is showing only one Exit interface

Below is the Static route in question:

set routing-options static route 205.0.0.0/8 next-hop 210.1.1.1

set routing-options static route 205.0.0.0/8 resolve


The INH is BGP ECMP route:

root@router-name> show route 210.1.1.1

inet.0: 75 destinations, 130 routes (74 active, 0 holddown, 1 hidden)

Limit/Threshold: 4/4 routes

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

240.1.228.0/22 *[BGP/170] 00:40:51, MED 10000768, localpref 100

AS path: I, validation-state: unverified

> to 211.1.1.1 via ae101.0

to 212.1.1.1 via ae102.0


However, the Static route pointing to this INH is showing only one Egress interface:

root@router-name> show route 205.0.0.0/8

inet.0: 75 destinations, 130 routes (74 active, 0 holddown, 1 hidden)

Limit/Threshold: 4/4 routes

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

205.0.0.0/8 *[Static/5] 00:41:07, metric2 0

> to 212.1.1.1 via ae102.0

 

Solution

Here is the lab route structure that we tested in lab:

201.201.201.201/32 --- Static route towards -- > 200.200.200.200
200.200.200.200 -- Static route towards ----- > 199.0.0.2 and 211.211.211.1

Output during problem state. Below output clearly shows that the Static route inherits only 1 Egress interface despite of its NH being ECMP

{master}[edit]
labroot@jtac-mx960-r2040-re0# run show route 201.201.201.201/32    

inet.0: 950782 destinations, 950784 routes (946817 active, 0 holddown, 3965 hidden)
+ = Active Route, - = Last Active, * = Both

201.201.201.201/32 *[Static/5] 00:05:43, metric2 0
                    >  to 199.0.0.2 via et-10/1/0.0
                    

We need to add this policy as I have shown below to have multipath in this case:

labroot@jtac-mx960-r2040-re0# run show configuration | display set | match multipath 
set policy-options policy-statement multipath_resolve then accept
set policy-options policy-statement multipath_resolve then multipath-resolve
set routing-options resolution rib inet.0 import multipath_resolve

Output after adding this policy. Once multipath-resolve is added, the Static  route inherits the ECMP behavior of its NH.

labroot@jtac-mx960-r2040-re0# run show route 201.201.201.201/32                         

inet.0: 950782 destinations, 950784 routes (946817 active, 0 holddown, 3965 hidden)
+ = Active Route, - = Last Active, * = Both

201.201.201.201/32 *[Static/5] 00:00:51, metric2 0
                    >  to 199.0.0.2 via et-10/1/0.0
                    to 211.211.211.1 via xe-6/1/3.0

 

Modification History

2024-05-24 : Article Created