7600: changing mpls experimental bit

Unanswered Question
Apr 26th, 2010
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is it possible to change mpls exeperimental bit

for traffic that enters a 7600 interface ?

i've tried with  "no mls qos mpls trust experimental"

configured under the input interface
but my attempt was unsuccessful
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Overall Rating: 3 (2 ratings)
lamav Mon, 04/26/2010 - 09:30
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I have not done it before, but from my understanding, you would have to do so as part of an MQC-based policy that you would configure and apply to the interface. Again, this is my understanding, not Gospel. Try doing it this way to see if you are successful.


Edison Ortiz Mon, 04/26/2010 - 09:31
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What do you want to change it to?

You can apply an input service policy to match on the MPLS EXP and set it to another MPLS EXP value.

If you want to clear any MPLS EXP value to 0, then simply enable MLS QOS globally and do not trust the port.



lamav Mon, 04/26/2010 - 10:06
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I believe he tried not trusting but ran into an issue, thats why I recommended what you did -- setting another policy to change it.


p.falconi Tue, 04/27/2010 - 00:05
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thanks Victor,

i've tried,unsuccessfully, with the following configuration

input interface is  WS-X6516-GBIC


policy-map SETEXP

  class class-default

   set mpls experimental imposition 3

interface GigabitEthernet3/1


switchport trunk encapsulation dot1q

switchport mode trunk

no mls qos mpls trust experimental

service-policy input SETEXP


sh policy-map interface GigabitEthernet3/1


  Service-policy input: SETEXP

    class-map: class-default (match-any)

      Match: any

      set mpls experimental 3:

      Earl in slot 5 :

5612026684 bytes

30 second offered rate 837104 bps

aggregate-forwarded 5612026684 bytes

Giuseppe Larosa Tue, 04/27/2010 - 00:24
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Hello Pierluigi,

if the input interface is a L2 trunk you may be able to set 802.1p CoS but not MPLS exp.

if you had used that service policy on a layer3 interface with MPLS enabled then you would be able to match packets on MPLS EXP bits and to set MPLS EXP bits

the reason is that on wire the frame will appear as an 802.1Q frame with next protocol MPLS

eth Header | 802.1Q 4 byte tag | MPLS 4 byte tag| IPv4 packet or other upper layer PDU

I would expect to be able to change MPLS EXP on a L3 MPLS enabled interface, not on a L2 802.1Q trunk.


I've checked on Config guide it should be possible to match on L2 ports I would try with only the input service policy applied


there are also EXP mutation maps but these are not supported on layer2 interfaces.

Hope to help


p.falconi Tue, 04/27/2010 - 23:52
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ok, thank you Giuseppe

since 7600 is able to change dscp even for l2 switched packet, i would expect it could change mpls experimental too,

but i was wrong



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