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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