From: jellyboy (jellyboy@gmail.com)
Date: Sun Feb 26 2006 - 19:15:46 GMT-3
Two points to note with the GRE tunnel is in this case:
Area 0---->R2-----NSSA STUB-----R5 ------> area 2
1. A GRE tunnel is formed between R2 and R5. Because all interfaces
and networks are running in an opsf area on r2 and r5, the tunnel
interfaces need an ip addressing scheme to communicate. This ip
addressing in this case 141.1.25.4-5 are used. First question is where
did this ip addressing materialise from? It is advertised as part of
the backbone and the network is picked up by the rest of the routers.
Can we just arbitrarily put in a network to make this GRE tunnel
perform?
2. By experimenting I have found that the backbone has to be extended
to the "end" of the stub, or nssa stub in this case. When I try to
configure the tunnel the other way around ie extend the area 2 to the
backbone by having the tunnel in area 2 it does not work. I get
%OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from
backbone area must be virtual-link error. I am guessing that ospf
treats the tunnel as another ospf area and creates another logical VL.
Can someone please clarify?
Really interesting!!
TIA, JB
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