DPT, MPLS and QoS

[p.jestin]

Hello,

I have some question about the support of MPLS over DPT on GSR plattform. DPT is supported since 12.0(9)ST.

Can DPT understand the EXP fied, and recopy it in the SRP Priority field?

Can DPT face congestion problem, in case of mismatch in the next hop? I mean that routing protocol can decide to use a next hop which might not be the closest at the SRP level, thus resulting in unefficient use of Bandwidth. As IP is not aware of the L2 topology, hos SRP can prevent from this?

Thanks for your advice,

Patrick.

[bwalchez]

Check out http://www.cisco.com/go/metroip

It has a lot useful info on DPT

[richardwatson]

No solution I'm afraid but a very similar question...

The only QoS command for SRP/DPT seems to be the "srp priority-map" which maps IP Precedence to the SRP Priority. This can't possibly work with MPLS tagged packets so would the command use the MPLS EXP bits instead?

I find it hard to believe there is not a MQC command for matching or setting SRP priority levels!

[danhut]

Guys,

On the GSR we do copy the MPLS EXP into the SRP priority field (not this is not the case on the c10720 which uses 0 for everything except packets in the priority queue).

There is a "set srp-priority" command in MQC to override this behaviour. From memory MQC for SRP on the GSR was coming around 12.0(26)S depending on the Engine type - you would need to check.

As for IP choosing the wrong path around the SRP ring, it will not since the whole ring has the hop count / cost. So the path around the ring will be determined by the STP protocol and distance a layer 2.

cheers