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[MX] Inconsistent output for "show route advertising-protocol bgp" with "rd-prefix" knob

  [KB34905] Show Article Properties


Summary:

This article explains why customers may get inconsistent output when they use the knob rd-prefix with the show route advertising-protocol bgp command.

Symptoms:

Inconsistent output or no output may be seen when the rd-prefix knob is used with the show route advertising-protocol bgp command.

The following example demonstrates the problem with no output:

show route advertising-protocol bgp 10.0.18.236 rd-prefix 36351:268540309:0/0  
<no output>

The following VRF table, however, has local routes that get advertised to the mb-bgp neighbors (remote PE or route reflectors).

show route advertising-protocol bgp 10.0.18.236 table GT-GC-ACCT.inet                                
 
GT-GC-ACCT.inet.0: 2006 destinations, 8012 routes (2006 active, 0 holddown, 0 hidden)
  Prefix    Nexthop        MED     Lclpref    AS path
* 10.188.184.0/26         Self                         100        I
* 10.249.136.0/22         Self                         100        I
Cause:

The above problem is caused by the missing advertise-from-main-vpn-tables configuration under protocols bgp, which is required to see the advertised routes by using the rd-prefix knob.

With the knob advertise-from-main-vpn-tables, routes are advertised from main VPN tables instead of the routing instance tables. When this knob is configured, the routes in the routing instance tables are first leaked into the bgp.l3vpn.0 global table and path-selection is run.

Further, VPN route advertisements happen from this bgp.l3vpn.0 table. Because the advertisements are done by using the bgp.l3vpn.0 table, filtering with rd-prefix will work. However, the routes need to be in the bgp.l3vpn.0 table for the rd-prefix knob to work with the command show route advertising-protocol bgp.

Solution:

To resolve this problem, add the following configuration under protocols bgp:

set protocols bgp advertise-from-main-vpn-tables

Observe the following output after adding the command under protocols bgp:

show route advertising-protocol bgp 10.0.21.252 rd-prefix 36351:1015:0/0  >shows output correctly for routes being advertised
 
bgp.l3vpn.0: 112 destinations, 177 routes (112 active, 0 holddown, 0 hidden)
  Prefix                     Nexthop                     MED     Lclpref    AS path
  36351:1015:169.62.168.0/22                   
*                         Self                 0       200        I
  36351:1015:169.62.188.0/22                   
*                         Self                 0       200        I
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