The MPLS-OPS Archive

[Christopher Poh <tvpoh@essex.ac.uk>]

Hi again,

Thank you for clarifying about BGP peering. What about if an interior router (non-BGP peer) would want to establish a connection to exterior routes? Would 
the LSPs for those routes be available to the interior router?


5/20/02 1:01:47 PM, Rajiv Asati <rajiva@cisco.com> wrote:

>Christopher,
>
>In a MPLS network, an ASBR, which is learning ipv4 routes via an eBGP 
>neighbor, typically doesn't allocate/advertise any label for those ipv4 
>routes that are advertised to its iBGP neighbors.
>
>         <-------AS#1-------->        <-----AS#2.--->
>         R1-------R2--------R3--------------P1---------------P2
>                 |
>                 R4
>
>So in the above topology, R3 may be learning 10,000 ipv4 routes from P1 
>(which is an eBGP neighbor) and may advertise those 10,000 ipv4 routes to 
>R1 and R4 (R3's iBGP neighbors). From R1 and R4 perspective, R3 is the 
>next-hop for all those 10,000 routes. So, R1 will have a label to reach R3 
>and it will use that single label to reach all those 10,000 routes.
>Similarly, R4 will also have a label to reach R3 and that label will also 
>be applied to any of those 10,000 prefixes.
>
>As far as peering to all the internal routes are concerned, MPLS provides 
>the ability to make core routers BGP free. In other words, R2 above doesn't 
>need to be an iBGP neighbor and so it doesn't need to know about 10,000 
>prefixes.
>
>Please let me know if I could be of more help.
>
>Rajiv
>
>At 09:13 PM 5/19/2002, Christopher Poh wrote:
>>Hi,
>>
>>How does an AS border router advertise and make known to all other routers 
>>within a domain about label/FEC binding information for every exterior 
>>routes it
>>carry? Does the router need to peer with all the interior routers in order 
>>to distribute this information?
>>
>>Hope someone could help me with this.



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