Hello Thomas
Rene addresses this question in the lesson:
Our CE routers have learned each other’s networks. There’s something interesting in the output above…normally when we redistribute something into OSPF then our prefixes show up as O E2 or E1, now we seem to have O IA prefixes. I’ll explain why in a bit…
He goes on to explain that when used with MPLS, OSPF considers the MPLS service provider backbone as an OSPF “superbackbone”, and the PE routers as ASBRs. The result is that routes that originated in an OSPF area connected to a PE router of the MPLS network are considered IA routes even if they have been redistributed from BGP. Take a look at the text in the lesson that describes it in detail.
Note that the PE routers are running two instances of OSPF. The instance with process ID “1” is the OSPF instance that is running within the BGP domain of the MPLS backbone using ASN 234. Now if you attempted to redistribute into that OSPF process, you would indeed need the “redistribute-internal” keyword, because that OSPF process is the process serving the specific ASN.
However, the redistribution took place on OSPF process “2” which is the OSPF process running between the PE and CE routers, which is outside of the BGP domain. This means, by definition, that the redistribution is taking place on eBGP routes, not iBGP routes. So the rule is not violated. Does that make sense?
I hope this has been helpful!
Laz