Simon writes:
I may be missing the point here, but in a situation where the net won't route longer prefixes than /20, doesn't punching a /24 hole in a /20 render the entire /20 unusable, not just the /24 - because the carrier who formally advertised the /20 now has to advertise a bunch of /21,/22,/23 and /24 prefixes to cover the remainder?
No. The /20 supernet continues to be advertised, and the new /24 net is also advertised. Since the /24 advertisement is more specific, traffic is routed to it; if it's not inside the /24 but inside the /20, the less specific route is used. For example, if carrier A advertises 192.168.0.0/20 and carrier B advertises 192.168.4.0/24, carrier C would have two routing table entries: 192.168.0.0/20 -> a.a.a.a 192.168.4.0/24 -> b.b.b.b and traffic for 192.168.4.2 would go to the more specific route b.b.b.b, while traffic for 192.168.5.4 wouldn't match the /24, and instead takes the less specific /20 route to a.a.a.a. It doesn't cause the /20 to be split into individual routes, but does create one extra routing table entry for each "hole". -- don --------- To unsubscribe from nznog, send email to majordomo(a)list.waikato.ac.nz where the body of your message reads: unsubscribe nznog