Understanding the network.pdf - Back to Home

gw1, gw2, gw4 3
gw1, gw3, gw4 3
gw1, gw2, gw5 3
As you can see, there are 13 possible routes just for routing traffic within the routing
domain for gw1. GW1 would also have to build tables to route traffic to each of its
connected intranets. Although the intranets can use default routes to forward their
traffic onto the backbone, the backbone network cannot. Because the whole ISP
internetwork operates as an AS, it needs to advertise routes for all its connected
networks. In other words, it needs to pursue an interdomain routing policy.
With an interdomain routing policy in place, the backbone routers run a single IGP
routing domain to manage routes between all the backbone routers. An EGP-like
BGP is used to exchange routing information between other ASs. The backbone
routers also run separate IGP domains for all the intranet exchange points and then
distribute the routing information between the intranet routing domains and the
backbone domain. This process looks something like what's illustrated in Figure
2.13.
Figure 2.13. The interdomain routing process model.