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MPLS EXP-BIT

class-map X

match ip dscp af41

!

policy whatever

class-map X

police 312000 24000 48000 conform-action set-mpls-exp-transmit 6 exceed-action set-mpls-exp-transmit 2

!

Question:

does the "set-mpls-exp-transmit" remark or encapsulate this AF41 to MPLS-EXP 6? My objective here is maintain "transparency" of the DSCP marking that is coming, meaning I would like this AF41 marking to remain untouched across my mpls backbone. My research tells me to do that I need to use set-mpls-exp with the "topmost" keyword which will give me DSCP Tunneling.

Can you guys clarify that for me? Am i reading this thing right?

1 REPLY

Re: MPLS EXP-BIT

Hi,

setting the MPLS exp bits does leave the IP DSCP bits untouched. The default behaviour by the way is to copy precedence to MPLS exp bits anyhow. With the policer you can remark in your MPLS network according to the SLA negotiated.

On some platforms you might have to use for example

policy-map CustomerIn

class business

police cir percent 25

conform-action set-mpls-exp-imposition-transmit 4

exceed-action set-mpls-exp-imposition-transmit 0

violate-action set-mpls-exp-imposition-transmit 0

Be aware that on the output from PE to CE you will have IP packets again. The exp bits are not copied to IP precedence by default. So either you use DSCP in the output policy on the PE with the customer values.

The other option is to map exp bits to a qos group and use this for the output policy. The advantage of the latter approach is that you do have consistent qos policies on a PE not refering to (different) customer markings.

Hope this helps

Martin

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