As seen in the introduction to routing video series, we talked about the differences between IGPs and EGPs. What is BGP for? And how does it compare to OSPF or IS-IS? Like we said OSPF or IS-IS are internal routing protocols that are used for carrying infrastructure addresses and not for carrying internet or customer prefixes. The design goal is to minimize the number of prefixes in IGP and to aid scalability and rapid convergence. BGP on the other hand, can be useful internally and externally. When it is used internally it's called iBGP and it is used for carrying some or all of internet prefixes across the backbone network as well as customer prefixes. When BGP is used externally it is called eBGP, and it is used to exchange prefixes with other ASes as well as implement routing policy. If you want your network to scale properly, you should not do the following, you should not distribute BGP prefixes into an IGP. You should not distribute IGP routes into BGP. You should also not use an IGP to carry customer prefixes.
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