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New Member

QoS query - mpls exp topmost

Hi Guru's.

Cisco 7609S running 12.2(33)SRE2

Im running a traffic gen to simulate a bit of remarking on the backbone.  I want to remark incoming traffic and then overload it to ensure its dropped on the backbone link.  What im finding is that the default class behaviour when trying to match on EXP value, is to match on topmost.  Even if i dont include the "topmost" command.  Does this mean i need to set topmost too?

I cant seem to see the dropped traffic on the INTER-SITE policy.  I suspect the EXP marking is not happening.

Example config.

class-map match-any EF
  match ip dscp ef
  match mpls experimental topmost 2
class-map match-any REMARK-EF
  match ip dscp af21
class-map match-any AF
  match ip dscp cs2
  match mpls experimental topmost 1
class-map match-any NC
  description Network Control
  match ip dscp cs6
  match mpls experimental topmost 6
policy-map INTER-SITE
  class NC
    bandwidth percent 1
  class EF
   police rate percent 10 burst 5 ms
     conform-action transmit
     exceed-action drop
  class Signalling
    bandwidth percent 1
  class AF
    bandwidth percent 70
  class class-default
     random-detect precedence 0 20 40

policy-map REMARK
  class REMARK-EF
   set dscp ef
   set mpls experimental imposition 2
  class class-default
   set dscp af12
   set mpls experimental imposition 1


Re: QoS query - mpls exp topmost


I'm not sure where you are using your route-maps exactly, but

shouldn't you use

set mpls experimental topmost ...

instead of

set mpls experimental imposition ...

in your policy-map REMARK



New Member

Re: QoS query - mpls exp topmost


Thanks for the response.  Actually the "topmost" match command is the default option, cannot change this.  On the 7609-S running 12.2(33)SRE1 when we specify a match command for EXP, it always seems to change the command to "topmost" but does not do this when setting the EXP.

To cut a long story short, no you dont necessarily have to remark as topmost.

I found the issue and it was a simple one.  I embarrassingly forgot to include the "mls qos" command globally.  After which, all the issues were solved and all the marking is working fine.

Thanks to everyone for their kind assistance.

Re: QoS query - mpls exp topmost

Can you present your complete topology?.

New Member

Re: QoS query - mpls exp topmost

Issue resolved.

Turns out i forgot to include the "mls qos" command globally.  Now the config works great.

Thanks a lot for your responses.