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Received BGP routes appear as unusable, hidden and inactive Technical Level
Symptoms
  • Checking BGP routes received from a peer with the command: # show route all users see that the routes are hidden, inactive and in some cases are unusable, for example:
    [Expert@Gateway:0]# clish -c "show route all" | grep 10.105
    B H i 10.105.133.0/24 via 172.28.228.7, unusable route
    B H i 10.105.138.0/24 via 172.28.228.7, unusable route
    B H i 10.105.143.0/24 via 172.28.228.7, unusable route

  • BGP is established with a peer and routes are received.

  • Routemaps or Inbound-filter-policy are configured to accept all routes from the BGP AS.

  • Running BGP debug (as per sk101399) you can see the following messages in the traces:

    • [DATE TIME] bgp_recv_check_asloop(7177): Routing loop, AS path exceeds AS limit (0) for Local AS 65001
    • [DATE TIME] bgp_rt_install_single_route(7727): 172.28.228.7 [eBGP AS 65002] Installing new route 10.105.133.0/24, pref unusable (-/-)

Cause

The BGP peer publishes the routes but it also prepend the local AS, which creates routing loop and make the route not preferable and in some cases unusable. You can see in traffic capture, in the message update packet, that the AS number is prepended.


Solution
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