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jskfanFlag for Cyprus asked on

split horizon in hub/spoke

can someone explain to me better than the explanation in the attached a file ?
Thanks
network.bmp
Routers

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Don Johnston

8/22/2022 - Mon
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Don Johnston

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ASKER
jskfan

-in hub and spoke,is it always one physical interface is connected to FR ?
-they mentionned "Instead of multiple interface" what did they mean by that?
Don Johnston

-in hub and spoke,is it always one physical interface is connected to FR ?

Usually. But it's not a requirement.

-they mentionned "Instead of multiple interface" what did they mean by that?

Instead of multiple "physical" interfaces.
ASKER
jskfan

in you example if we had 2 physical interfaces going from the HUB to site A and B, would this work just like having subinterfaces?
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fblack61
Don Johnston

Yep. But you'd never really do that. It would defeat one of the big cost benefits of frame-relay.
ASKER
jskfan

<<Yep. But you'd never really do that. It would defeat one of the big cost benefits of frame-relay.>>
what do you mean?
Don Johnston

One of the benefits of frame-relay is being able to terminate multiple locations on a single interface. That means a single local loop. So you can have 12 remote offices connected to the HQ office and only need a one local loop.

Why would you want to spend all the additional money on 1) a router with 12 serial interfaces and 2) 11 additional local loops?
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ASKER
jskfan

even whe using no ip split horizon?
Don Johnston

You're over complicating it.

Sub interfaces allow a router to take a single physical interface and treat it as if it were multiple interfaces. That way, the split horizon rule does NOT cause a problem with distance vector routing protocols.
ASKER
jskfan

what I understand is:
Split Horizon is telling the interface or subinterface if you a network is learned from interface A don't re-advertize through interface A,but advertize it through interface or Subinterface B,
in this case I don't see why the local loop will occur if you have may physical interfaces or just one interface with many subinterfaces.
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William Peck
Don Johnston

Local loop is a term that refers to the physical circuit that connects your router to the frame-relay provider POP (Point Of Presence). This can be a DS0, fractional T-1, full T-1, fractional T-3 or even a full  T-3.