BGP LABEL LSP

Hi

I have a topology like this

                           ____________ibgp______________

   R5------------------R1-------------------R2-----------------------R3
             ibgp ebgp ebgp

R1 and R3 are running iBGP in AS 100 and R1 and R2 are running eBGP with R2
in AS 200 and respectively R2 and R3 are eBGP neighbors.

There is no physical connection between R1 and R3 . There is an iBGP peer
between R1 and R3 via R2 which is a eBGP peer with both R1 and R3

Now R1 is a RR and R5 and R3 are clients

MPLS is enabled between R1 and R2 and R2 and R3. But there is no LDP or
RSVP enabled on those interfaces.I have just enabled the forwarding place
saying that this interface can receive labelled packets.

R3 is learning R5's routes via R1's iBGP connection with a next hop as R5.

R5's loopback is advertised as ebGP route to R2 from R1 and it is passed to
R3 from R2 as eBGP route.

Now when R1 is sending as Ipv4 Unicast routes with Labels on it. ( with
Send label option ) to R2.

R2 is also having the send label in the eBGP peering with R3 .

So now for R3 to reach R5s loopback there it should use a label sent from
eBGP neighbor R2.

So now here is the problem part. I dont have a label for the prefixes ( ie
R5 advertised prefixes ) and i only have the next hop which is R5 loopback
label ( ie advertised by R2 to R3 ) .

So when R3 is sending traffic to R5's prefixes, will it use the BGP label
to R2 and R2 will use the BGP label to reach R1 and then R1 will strip the
label and do a normal routing lookup to send traffic to R5

Will BGP label forms an LSP ?. When a next hop in a BGP table is again
learned by BGP, will it use the BGP label to send the traffic ?

Without the prefix label , will only the next hop BGP label will work to
form LSP ?

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Received on Mon Dec 10 2012 - 22:41:13 ART