[c-nsp] MPLS QoS at SPA-5X1GE-V2, SIP 400, 7604RSP720 (Ruzhanskaya Olga)

[Nigel Roy]

Hi Olga,

Came across the same problem as you recently on some of our 7600 PE routers.

Like you I raised it as a TAC case as I thought it was a bug but after a couple of weeks the TAC engineer discovered exactly what you say.

For locally routed packets (IP-IP) the set mpls exp overwrites the DSCP value. Works fine when going from IP-MPLS though! Because you can never be certain whether packets are going to be locally or MPLS switched the command becomes useless.

They did say they would try and find an alternative but they never cam up with anything.

The alternative I have tested is what we are thinking of using. This uses the global dscp-exp mutation map.

This is enabled by default but obviously is overridden by the policy-map set mpls exp command.

This worked in the tests I have done but the documentation states "“This command is supported in PFC3BXL or PFC3B mode only.” This is not a problem for us as the hardware we are using matches the requirement.

The following is used in global config to modify the default setting for the dscp-exp map:

mls qos map dscp-exp 46 to 5
mls qos map dscp-exp 10 18 26 40 45 to 2
mls qos map dscp-exp 1 2 3 4 5 6 7 8 to 1

The only other possibility I started to look at was "table-maps" however they were not supported in the IOS we use and I am not even sure if there is an IOS for the 7600s that supports them.

Regards Nigel


> Hello List!
>
> In our MPLS network we use 7604RSP720 with SPA-5X1GE-V2 installed
> in SIP 400 as PE router, where clients services terminates. As in
> MPLS edge, we perform "typical" traffic classification and marking.
> Standart policy-map looks like this (matching based on DSCP,
> marking with MPLS EXP): Policy Map Network-VoIP-In Class qos-
> realtime set mpls experimental imposition 5 ... Class class-default
> set mpls experimental imposition 0 Class Map match-any qos-realtime
> (id 21) Match ip  dscp ef (46)
>
> For example, we have two subinterfaces, gi3/0/0.210 and
> gi3/0/0.211. Both of them have policy-map looks like described one.
> If packet enters gi3/0/0.210 with DSCP=EF and go to gi3/0/0.211, it
> appears with DSCP=CS5. Is this normal?
> For 76x, it is.
> Because of 76x platform QoS realization traffic local for router
> (IP-IP), router overwrites DSCP value of packet when such policy-
> map in use:
> http://www.cisco.com/en/US/docs/routers/7600/ios/12.2SR/configuration/
> guide/mplsqos.html#wp1475897
>
> I've even opened a case, but the best proposed approach was to
> distinguish with ACL IP-IP traffic and IP-MPLS traffic. This is a
> bad solution for us: increased load on router, many hand-work and
> we have hundreds of such circuits..
>
> We are trying to resolve this problem from April - and no
> sufficient solution.. Maybe someone have resolved this?
>
> P.S. "no mls qos rewite ip dscp" doesn't work properly on PFC MPLS,
> already tried.
>
> Best regards,
> Olga
>
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp archive at
> http://puck.nether.net/pipermail/cisco-nsp/