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, 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:


  1. is a class-A address, so you’re telling BGP you want to advertise Since you only have an IGP route (connected via loopback) to, 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 (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 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 will be enough to advertise that subnet to its peer.

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