So, how do ISPs typically advertise their own internal address space in BGP? By internal address space, I mean to say: loopbacks, customer P2P connections, and customer assigned addressing. Given that I doubt anyone accepts prefixes longer than a /24, I assume these have to be aggregated into a larger network and then advertised as a single prefix (ex: 12.0.0.0/9 for AT&T).
What I'm not sure of, however, is where to aggregate these routes at, and how. Do you do an BGP aggregate address on every edge router? Do you redistribute a static route to null0 on every edge router? Or do you generate these routes on only a few core routers? Is there some other way that I'm not considering?
Also, do you insert the longer prefixes into your BGP routinig table at all? Or do you keep them strictly in the IGP?
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