[c-nsp] Preserving CoS with xconnect on ME3600X

[Lobo]

I was under the impression that the "rewrite ingress tag pop 1 
symmetric" was required in order for the xconnect to work?  Removing it 
seems to break the xconnect as traffic no longer goes across it.

So is MQC with qos-groups is the only way to preserve the markings with 
this platform?

Jose

On 11/6/2012 3:14 PM, Pshem Kowalczyk wrote:
> Hi,
>
>
> On 7 November 2012 08:04, Lobo <lobotiger at gmail.com 
> <mailto:lobotiger at gmail.com>> wrote:
>
>     Hi everyone.  I was hoping I could get some help with an EoMPLS
>     config I'm working on between an ME3600X and an ME6524 and being
>     able to preserve the CoS field values.
>
>     The xconnect pseudowire it actually up and able to pass traffic so
>     that's not a problem.  The issue is that any CoS values I assign
>     to the data packets seem to get overwritten on the ME3600X in the
>     service instance config.  This is a rough topology of what I'm using:
>
>     Traffic generator --- 3750 --- ME3600X ---pseudowire over mpls
>     cloud--- ME6524 --- 3750G --- Traffic generator
>
>     What I see happening (going from left to right) is that the 3
>     different CoS values (5,3,0) all get overwritten to zero as soon
>     as the traffic goes over the xconnect.  LDP labels are also sent
>     as exp zero.
>
>     In the opposite direction where the xconnect starts on the ME6524,
>     the CoS values are copied over to the exp values all the way to
>     the ME3600X until it passes through the service instance config.
>      Once I inspect the traffic on the 3750 switch, I see all my
>     traffic arriving with CoS 0.  Note that DSCP is preserved in both
>     directions.
>
>     I'm curious if there is some global command for the ME3600X or
>     some additional config that I need to do on the service instance
>     in order to somehow copy the CoS value to EXP bit.  Or do I have
>     to do more inspection and writing of values via MQC?
>
>     Here is the config I have for the xconnect on the two platforms.
>
>     ME3600X
>
>     interface GigabitEthernet0/8
>      switchport trunk allowed vlan none
>      switchport mode trunk
>      load-interval 30
>      speed 100
>      duplex full
>      service instance 3801 ethernet
>       encapsulation dot1q 3801
>       rewrite ingress tag pop 1 symmetric
>       xconnect 172.28.110.2 666 encapsulation mpls
>      !
>
>     ME6524:
>
>     interface GigabitEthernet1/1.3801
>      encapsulation dot1Q 3801
>      xconnect 172.28.110.2 666 encapsulation mpls
>     !
>
>
> Your problem is caused by the following line in 3600x config:
>
> rewrite ingress tag pop 1 symmetric
>
> that line removes the vlan tag and the COS bits with it, so when the 
> frame hits the PWE3 there is no information about what class the 
> traffic belonged to originally, just plain ethernet frame.  One way to 
> make it work is to create a set of policies on both 3600x and 6524 
> that inspect the incoming packets and copy the COS bits into EXP/QoS 
> bits of the MPLS label and then have a symmetric set of policies on 
> egress to copy bits from EXP/QoS back to COS (AFAIK 65xx does it 
> automatically, if not configured otherwise). I believe you have to use 
> qos-groups on egress, as MPLS markings do not survive till the egress 
> policy processing.
>
> Between two 3600x you can make it also work if you do not pop the VLAN 
> tags (then PWE3 carries ethernet frame with VLAN tags).
>
> kind regards
> Pshem
>