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New Member

Duplicate AS number question

Hi I have a basic question about the duplicate AS number. 

Here is the topology, features like as-override or remove-private-as has not been enabled on PE. CE has default route pointing back to PE.

10.0.0.0/24 CE1(AS number 65100) - (AS number 65999) PE1 -- MPLS cloud -- PE2 (AS number 65999) - (AS number 65100) CE2 20.0.0.0/24

I want to know if site 1 can talk to site 2, thanks.

 

Cheers, Leo 

  • MPLS
1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Blue

LeoApologies, i may have

Leo

Apologies, i may have misunderstood your question.

I was assuming the default route was being sent via BGP from one site to the other but on rereading it you may not be talking about that. 

If you mean each site has it's own default route poiting to it's PE and this is the route used to send traffic to the other site then yes they can communicate.

The AS PATH attribute check is only relevant if the routes are being exchanged between PEs and then passed on to the CEs.

Jon

3 REPLIES
Hall of Fame Super Blue

LeoWithout extra

Leo

Without extra configuration no they cannot talk to each other. 

The reason being an EBGP router will drop a route if it sees it's own AS in the AS PATH.

You can however on the CE configure -

router bgp 65100

neighbor <PE peer address> allowas-in <x>  <-- where x is the number of times the CE's own AS can be seen in the AS PATH attribute.

There is the possibility of causing routing loops in certain topologies although from the topology in your diagram it should not be a problem.

Jon

Hall of Fame Super Blue

LeoApologies, i may have

Leo

Apologies, i may have misunderstood your question.

I was assuming the default route was being sent via BGP from one site to the other but on rereading it you may not be talking about that. 

If you mean each site has it's own default route poiting to it's PE and this is the route used to send traffic to the other site then yes they can communicate.

The AS PATH attribute check is only relevant if the routes are being exchanged between PEs and then passed on to the CEs.

Jon

New Member

Thanks Jon, that's what I

Thanks Jon, that's what I want to confirm. 

 

Cheers, Leo

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