1. Kireeti Kompella Juniper Networks
ECMP with RSVP-TE
Kireeti Kompella
Juniper Networks

2. Outline Current situation LDP vs. TE ECMP NxTE LSPs vs. TE ECMP MLSP
Signaling
Next steps

3. Current Situation
An MPLS network relies on an underlying LSP mesh connecting all edge devices
In principle, this could be IP tunnels
This may be based on LDP or RSVP-TE, or sometimes a combination of LDP on the edge and RSVP-TE in the core
There are a number of attributes that dictate the design

4. LSP Design Attributes Attribute RSVP-TE LDP Ease of configuration ✖ ✔
FRR
TE, CAC, BW guarantees
ECMP

5. Either/or … Why Not Both?
Can one create an underlying mesh of tunnels that has both TE and ECMP?
Yes!
Introduce the notion of a “multi-path” TE LSP signaled using RSVP
Several “sub-LSPs” under one container tunnel
Note that the state required for RSVP-TE is still higher (O(N^2)) than that for LDP (O(N))

6. Illustration (LDP vs. TE ECMP)
200 Mbps LSP from A to B
100 25
160 40 A B

7. NxTE LSPs vs. TE ECMP MLSP
200 Mbps MLSP from A to B vs. 5 40Mbps TE LSPs A B

8. Discussion
NxLSPs requires N things to provision and manage; an MLSP is a single object with N sub-objects
An MLSP with N sub-LSPs may (depending on the topology) have significantly less state than N LSPs
The use of equi-bandwidth sub-LSPs can also significantly reduce state

9. Discussion Computing the NxLSPs is done pretty much independent
The number and placement of the LSPs may not be optimized for the purpose of ECMP
Failure of one of the N LSPs means that the overall bandwidth drops (e.g., by 40Mbps)
Failure of one sub-LSP can be compensated by the head end bumping up the bandwidths of the rest

10. Signaling The current draft talks a little bit about signaling
Basic idea: signal N sub-LSPs, and tie them together via a Session object to form an MLSP
Introduce the idea of “equi-bandwidth” sub-LSPs
If this draft is of interest, the signaling piece would probably need more work
Have to work out how FRR and DiffServ-awareness work in the context of MLSPs

11. Next Steps
Get a sense of how useful this is