OSPF Redundancy

[davidcriollo]

I'm reading Chapter three of the Enarsi book (OSPF) and it states the following: From R1's perspective, the serial link between R3 and RA is missing. From R4's perspective, the Ethernet link between R1 and R3 is missing. Based on my understanding, from R1's viewpoint, the network 10.34.1.0/24 does not exist. In such a scenario, what would happen when the network 10.1.1.0/24 wants to communicate with 10.34.1.0/24?

[MHM Cisco World · Accepted solution]

there is no RA in topology
and if you meaning RA id R4 then

there is physical link appear in first part of image you share 
there is virtual link appear in part 2 and part 3 of image you share.
but why physical differ than virtual, simply the OSPF will select path through short cost link and R3 have two link one of them will select other will no that why it disappear from image. 

[davidcriollo]

yes, I wanted to say R4, my bad, but the thing that I do not understand is why 10.34.1.0/24 is not visible from R1's perspective. I do not see a virtual link in the topology.

[MHM Cisco World]

Nop, R1 can see it, but the author of book show only subnet of LO or LAN  connect to Router not  subnet of Link interconnect the routers
I will prepare lab for you and show you how this prefix appear in each router. 
hope finish it tonight. 
MHM

[davidcriollo]

I did build that topology this morning on Packet tracer and yes, it was there. I think that I am understanding. So the serial link has a higher cost that others link so that's why the router will choose Ethernet link rather than serial links. 

[MHM Cisco World · Accepted solution]

You are totally correct.

[Flavio Miranda]

Hi @davidcriollo 

  If you try to ping R4´s interface from R1, it will fail, unless it has a default route to another router.