Hi,

Just to add to this.. what you are seeing is the established session between
two routers. In reality (and by default) both routers will be listening on
port 179 - you'll see that with "show tcp brief all numeric". If you're
really interested in the connection you can check it out with "show tcp tcb
[TCB value from first column]".

PE1#sh tc br a nu
TCB       Local Address               Foreign Address             (state)
[ ... ]
6567EEDC  0.0.0.0.179                 10.10.10.122.*              LISTEN
6567E418  0.0.0.0.179                 10.10.10.121.*              LISTEN
[ ... ]

Having 0.0.0.0 for local address means it will accept a connection to any
address it identifies as belonging to the router. You should have one listen
line for each neighbor you've configured (at least on 12.2SB and 12.2SR I
checked it with)

Check out the RFC and earlier mails on why there's only one session instead
of two between the routers :)

There's an ietf draft (draft-ietf-idr-bgp-multisession-04) about having
multiple active sessions between peers - for example one for each
AFI/SAFI.... No need to worry about that for R&S though. :)



Kaj



> From: Taqdir Singh <[email protected]>
> Date: Tue, 18 Aug 2009 06:38:53 -0700
> To: <[email protected]>
> Subject: [OSL | CCIE_RS] BGP listens on TCP port 179
> 
> R0#show tcp | in port
> Local host: 10.10.10.1, Local port: 179
> Foreign host: 10.10.10.2, Foreign port: 23818
>  
> R1#show tcp | i port
> Local host: 10.10.10.2, Local port: 23818
> Foreign host: 10.10.10.1, Foreign port: 179
>  
> BGP listens on TCP port 179 , according to above output I see only router R0
> is listening on port 179.. but R1 is on 2318. Shouldn't be we have separate
> TCP connection on R1 with listening port 179 ?  

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