MPLS TE sub-pool oversubscription

[dknov]

Hi,

Are DS-TE LSPs allowed to use more bandwidth than allowed by sub-pool or are they limited similarly to the way LLQ max size is limited by a figure specified in "priority" command?

I presume that LSP setup will fail in this case, right?

Thanks,

David

[Harold Ritter]

TE works at the control plane level only. No admission control is performed on the data entering the tunnel.

Hope this helps,

[dknov]

Hi,

Maybe my analogy to LLQ was a bit misleading, what I actually meant was let's say that you have an interface with sub-pool bandwidth configured as 1000Kb, if you try to signal a DS-TE Tunnel which requires 2000Kb, will a tunnel come up or will it stay down because its bandwidth is limited by 1000Kb specified for the sub-pool?

Thanks,

David

[Harold Ritter]

The tunnel would definitely not come up since the BW requirement can not be satisfied from the specific BW pool.

Hope this helps,

[dknov]

Hi,

I see, so it looks like it's unidirectional, meaning non DS-TEs can use sub-pool pool if needed (will be rerouted/reoptimized if DS-TE needs the sub-pool bandwidth), but DS-TEs can't use global pool, right?

David

[Harold Ritter]

That is correct. The global pool is the total reservable BW, whereas the subpool is a subset of that reservable BW.

Hope this helps,

[Harold Ritter]

Just as a precision, the reroute/reoptimization of the non DS-TE will only occur if the priority of the DS-TE tunnel is lower.

Hope this helps,

[mheusinger]

Hi Harold,

from a control plane perspective the sub-pool bandwidth is just another constraint to be met. Fine. But how do you treat the sub-pool bandwidth during interface overload situation? There is definately less bandwidth for LLQ/CBWFQ when a sub-pool reservation is in place. But will there be a "priority" like behaviour (a policer coming with it)or is the sub-pool treated like "bandwidth" with a minimum bandwith guarantee?

My perception so far is that the latter is true.

Martin

[oettls]

Hi Martin,

TE (and also Diff-Serv aware TE) is a control plane feature only.

There is no enforcement of TE reservations in the data plane. So no 'automatic' queueing mechanisms like in traditional RSVP (non TE) admission control. A way of bringing TE and Diff-serv queueing together would be to reserve the amount of sub-pool bw per interface in a LLQ. Then make sure that only traffic engineered data makes it into the LLQ and enforce the reserved bw at your network edge (ingress policing). This way you can give an end-to-end guarantee for your sub-pool traffic.

hth

cheers,

Stefan

[mheusinger]

Hi,

thanks I already got it from reading

MPLS Traffic Engineering--DiffServ Aware (DS-TE)

http://www.cisco.com/en/US/products/sw/iosswrel/ps1838/products_feature_guide09186a00801b1c0b.html

Happy New Year

Martin