BGP network command

– without mask subcommand, we need to have a subnet in the routing table, that belongs to the classful network. But in my lab, even I have a subnet 5.5.0.0/16, I still don’t see it in the BGP Table:

However, with the mask subcommand, and by specifying the subnet, I can see it. I don’t still get it:

3 comments

  1. 5.0.0.0 is a class-A address, so you’re telling BGP you want to advertise 5.0.0.0/8. Since you only have an IGP route (connected via loopback) to 5.0.0.0/16, it won’t be advertised via BGP.

  2. thanks for the clarification Aaron, I didn’t see your comment until now :-)

  3. Its the effect of Auto-summary.
    If you have auto-summary disabled and advertising a classful network 5.0.0.0 (with mask / without mask – default network mask is used i.e. /8) will trigger BGP to look for the exact route in the routing table, i.e. you need to have 5.0.0.0/8 in the routing table.

    On the contrary, if you have it enabled, then a subnet of the major network included for advertisement in our case 5.5.0.0/16 will be enough to advertise that subnet to its peer.

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