Distance vector with split horizon

[sam daniel]

• Which router will come to know first (if they are connected in star topology and any router except the central one is broken ) in distance vector with split horizon ... Please explain 
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• Thanks 

[MHM Cisco World]

Can you more elaborate 

Thanks 

MHM

[Joseph W. Doherty]

What's the actual topology, in detail?

What exactly "broke"?

What exactly do want to be known first?

Are you trying to understand split horizon?  If so, perhaps this will help: https://www.computernetworkingnotes.com/ccna-study-guide/split-horizon-explained-with-examples.html

[David Ruess]

Regardless of any topology (star, ring, mesh, etc) the rules of split horizon are the same and say to not advertise a route out the same interface that you are using to get to that network.

For example, if I learn about the 10.1.1.0/24 network through my g0/0 interface and I use my G0/0 interface to reach that network.  If I learned it from another neighbor/interface as well I will not advertise that network out my G0/0 interface, becasue thats the interface I am using to get to it and they already know about it.

Hope that helps

-David

[Joseph W. Doherty]

David correctly states what split horizon does, i.e. it suppresses advertising a network back out the interface it was learned on.

The reference I provided in my prior reply shows how a DV routing protocol not doing this can get into a routing loop.

I suspect there's more you might be trying to understand the way your OP is worded (asking about star topology and first to know).  One point that can confuse, routing protocols try to avoid creating routing loops but during a topology change, temporary routing loops, or black holes, can be formed until the network fully reconverges.

[Richard Burts]

As others have commented the description of the environment is pretty vague. How do you have this star? Pretty clearly there is a center router and some number of other routers. Do the other routers connect just to the central router (so that the spoke routers each have a single connection)? Or do spoke routers connect to neighboring spoke routers?

And can we get clarification about what it means to be "broken"? I am assuming that essentially it means that a router stops communicating.

Despite all the things that we do not know I believe that there is a pretty simple answer to the question in the OP. "Which router will come to know first" and the answer is that the first to know would be the router(s) to which the broken router connected and with which it has stopped communicating.