How traffic is directed in MPLS network? Via ldp LSPs or via RSVP LSPs

Unanswered Question
Aug 1st, 2012

My question is basicly to understand how traffic is treated.

Lets assume our topology is :


1-) if we just enable MPLS under all interfaces, LDP labels are exchanged with each peer. At that moment   RIB, LIB, FIB and LFIB are created on all routers. So LDP LSPs are created dynamicly. but  If i ping "loopback D"  from router A, there will be IP routing or LABEL switching.  will routing make routing by looking IP address at each hop or labels will be swapped at each hop ?

2-) If we enable MPLS traffic engineering capability and create a tunnel interface between router A and router D, vice versa. At that moment, Router A will have :

-simple IGP reachability to Router D,

-Dynamic LDP LSP  and

-RSVP tunnel.

what about now, Which one of the paths above  my traffic will follow ? do I have to direct my traffic to tunnel interface signaled via RSVP. Is there any precedence for choosing the path that traffic will be addressed ?

I have this problem too.
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Ivan Krimmel Wed, 08/01/2012 - 05:47


1. ip lookup will be made at the first and last hops only, everywhere in the middle of the network datagarms will be label-switched(if you have consistent LSP from A to D).

2. it is really better to set up and look/understand yourself, however to your attention I would like to bering the following doc:

which will shed some(if not all) light on that matter.


enderkaran Wed, 08/01/2012 - 06:05

for second secenario, i have found that I have to write

"tunnel mpls traffic-eng autoroute announce " other wise traffic will always follow LDP signaled paths. In order to get all traffic inside "tunnel" we should execute that command.  once you write that command you see that ;

Before executing command;

R1#sh ip route


O [110/129] via, 00:07:08, serial0/0

R1#show mpls forwarding-table

18     18        0          Se0/0      point2point

After executing command;

R1#sh ip route


O [110/129] via, 00:07:08, Tunnel0

R1#show mpls forwarding-table

18     Pop tag [T]        0          Tu0        point2point 

Hope you see my point, router doesnt decide to use RSVP signaled LSP itself, we shoud trig router to use RSVP signalled LSP.


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Posted August 1, 2012 at 5:34 AM
Replies:3 Avg. Rating:
Views:1519 Votes:0
Tags: mpls, ldp, rsvp-te

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