[c-nsp] catalyst 6500 not rewriting CoS / 802.1p bits

[Phil Bedard]

If the port is marked as untrusted, the PFC still marks the packet  
with an internal DSCP value of 0 on ingress, so the "mls qos cos 5"  
command in this instance won't do what you want.   You can configure  
the "mls qos marking ignore port-trust" command, then the PFC will not  
rewrite the port cos value you set.  Another option is to use a policy- 
map to set certain traffic to trusted.  You could also set the ingress  
DSCP value with a policy-map and use the dscp-to-CoS map to set the  
correct egress cos.  The default map sets DSCP 40-46 to 5 (divides by  
8).

There may be another way as well that I'm missing.  I don't know that  
setting the port to trusted state will work, I believe for a trunk it  
will ignore the mls qos cos value.

Phil


On Feb 9, 2008, at 6:20 PM, Vladimir Ivashchenko wrote:

> Just to make sure I'm clear: "802.1p value for packets going out  
> from Gig2/1 is set to 0" - I mean packets received
> from Gig2/1, going to the Linux box on another interface, have CoS  
> bits set to 0, despite "mls qos cos 5" on the
> Gig2/1. The sniffer is running on the Linux box.
>
> On Sun, Feb 10, 2008 at 12:31:37AM +0200, Vladimir Ivashchenko wrote:
>
>> Hi List,
>>
>> We cannot get Cat6500 to rewrite CoS values (802.1p bits).
>>
>> Configuration is
>>
>> mls qos
>> no mls flow ip
>> no mls flow ipv6
>> no mls qos rewrite ip dscp
>> no mls acl tcam share-global
>> mls cef error action freeze
>>
>> interface GigabitEthernet2/1
>> switchport
>> switchport trunk encapsulation dot1q
>> switchport mode trunk
>> no ip address
>> load-interval 30
>> wrr-queue queue-limit 40 30
>> mls qos cos 5
>> no cdp enable
>> spanning-tree portfast trunk
>> no mls qos trust
>>
>> We have a sniffer connected to dot1q trunk on another port. The  
>> sniffer shows that 802.1p value for packets going out
>> from Gig2/1 is set to 0. We have tried searching Cisco site and  
>> playing with various commands, but did not succeed. IOS
>> 12.2(18)SXF5.
>>
>> Catalyst 3560 has "mls qos cos override" command, which seems to do  
>> the trick, but this command is not available on
>> Catalyst 6500.
>>
>> -- 
>> Best Regards
>> Vladimir Ivashchenko
>> Chief Technology Officer
>> PrimeTel, Cyprus - www.prime-tel.com
>> _______________________________________________
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>
> -- 
> Best Regards
> Vladimir Ivashchenko
> Chief Technology Officer
> PrimeTel, Cyprus - www.prime-tel.com
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