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Cisco 7200s / MPLS EXP Bits / TOS / Default Mapping

I found the following information while researching this topic.

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"The edge LSR that imposes the MPLS header needs to set the experimental field to some value. By default, Cisco IOS® Software copies the three most significant bits of the DiffServ code point (DSCP) or the IP precedence of the IP packet to the EXP field in the MPLS shim header. This action happens when the MPLS header is initially imposed on the IP packet. Another option is to define a mapping between the DSCP or IP precedence and the EXP bits. This mapping can be configured using the set mpls experimental or the police commands in the Modular QoS CLI (MQC)."

http://www.cisco.com/warp/public/cc/pd/iosw/tech/mpotc_qp.htm

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We tested this functionality and it works as advertised (ie. IP Precedence of 7 maps to EXP Bit 7).

Is there a way to turn off this default behavior? Ideally, we would like to mark EXP bits based on our network policies instead of our customers DSCP/IP Precedence bits.

Right now, it looks like we would need a service-policy on every customer interface in our network. Most customer interfaces would have a generic service-policy that sets the EXP bits on their traffic to 1 for example. High priority customers would have a service-policy thats set the EXP bits to 5. We are looking for a way to forgo the generic service-policy on every customer interface so that only priority customer interfaces require a service-policy statement.

Anyone found a creative solution for this type of setup?

Thanks.

Jeff Chambers

1 REPLY
Cisco Employee

Re: Cisco 7200s / MPLS EXP Bits / TOS / Default Mapping

As far as I know, you need to explicitly reset the EXP bits if you want to prevent the customer to arbitrarly setting its value.

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
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