BGP Null 0

[sk82]

I see a route to a specific destination which says it is known via BGP type, locally generated - directly connected, via Null0.

I can also see aggregate-address to specific route with a wider range of /16 with the attribute-map configured. 

What does this mean ?

[MHM Cisco World]

there are two approach to summary prefix in BGP
1- use summary address to null0 and advertise this summary under BGP 
2- use aggregate address under BGP 

there is no different which approach you use but it common that engineer use null0 summary address because it so easy 

MHM

[Giuseppe Larosa]

Hello @sk82 ,

a static route with outgoing interface null0 can be used in combination with a network command under BGP to create an aggregate.

All packets with a destination not matching a more specific prefix will be silently discarded  ( null0 = bin)

The more modern way to create an aggregate in BGP is to use the aggregate-address command.

For the aggregate-address to work a component route must be in the BGP table, if this component route is a route to null0 this route will never disappear and the aggregate-address is always advertised.

Hope to help

Giuseppe