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BPX traffic routing and bandwidth 9.2.38

I have question relating to Class of Service (COS) and preferred routing (Pref), which one has the highest priority?

9.2.38 BPX software

If you have a back-up link, say DS3 (96000cps) and across that link you have 8 E1 CBR services (5447cps * 8 = 43576cps) each with their COS set to 0, and across the other trunks in the N/W you have the following COS 0 services;

CBR 17500cps utl 100%

CBR 17500cps utl 100%

CBR 60000cps utl 100%

There is also lots of COS 1 services across the other trunks (not the DS3)..

During N/W failure that takes down all other trunks and the only way for any service to successfully operate is across the DS3.

Will the 8 E1 services stay on that DS3 or will the COS 0 services listed above bump them off the DS3. If so, which COS 0 services will come over 1st, it's my understanding that the bigger the BW and UTL % will determine this.

So with the 60,000cps service going across first, which of the two 17,500cps go across next.

We have 1000cps for statistical reserve, so at least 1 17,500cps service should make it across as well.

If any one can help that would be excellent, otherwise I'll run it through our lab N/W.


David K.


Re: BPX traffic routing and bandwidth 9.2.38

Can you post the results of your lab test here?

Cisco Employee

Re: BPX traffic routing and bandwidth 9.2.38


In this situation, the 8 E1 cons will remain, then maybe the 60K con, then one of the 17.5k cons...let me explain.

It all depends on where the "local" side of the connections are. If they are all on different nodes, then it will be a race to see which nodes first sees the trunk fail, and then trys to reroute first. If they are all local on the same node, and all have the same path (I guess so because this is the only tunk left) then the cons will route from largest to smallest (cps x % util, as you stated). If they are exactly equal, then I'm not sure which one goes first. I'd guess the one with the lower card number, but that's just a guess.

In your situation, if you prefer on 17.5k CBR con over the other, then I suggest setting the COS onthe one you don't want to route to 1.

In 9.3 SWSW, we have re-instituted Priority Bumping, and you can use that to force some of those E1 CBR cons off if that is something you'd be interested in.