From: Lord, Chris (chris.lord@lorien.co.uk)
Date: Fri Aug 13 2004 - 09:03:25 GMT-3
Bob,
Thanks for the response. I understand that setting the precedence of a packet will be preserved across the switch and it will egress with the ToS in tact. However, if I want the 3550 switch itself to prioritise the traffic and for the egress queues to prioritise the traffic, surely you have to explicitly tell the switch, somehow, to trust the ip-precedence settings??
Usually if packets were arriving with precedence 5 already set you would enter the command "mls qos trust ip-prec" on the switch port. However, if you apply a per-port-per-vlan policy map it won't let you enter the command.
Chris.
-----Original Message-----
From: Bob Sinclair [mailto:bsin@cox.net]
Sent: Friday, August 13, 2004 12:16 PM
To: Lord, Chris; ccielab@groupstudy.com
Subject: Re: 3550 per-port-per-vlan and qos trust
Chris,
If you enable mls qos on the 3550, then all ports will be UN-trusted by
default. However, if you set precedence in an inbound policy-map, you do
not need to also trust inbound precedence. The default precedence-dscp map
will preserve your precedence across the switch.
HTH,
Bob Sinclair
CCIE #10427, CISSP, MCSE
www.netmasterclass.net
----- Original Message -----
From: "Lord, Chris" <chris.lord@lorien.co.uk>
To: <ccielab@groupstudy.com>
Sent: Friday, August 13, 2004 7:07 AM
Subject: 3550 per-port-per-vlan and qos trust
> By default a 3550 will trust cos when using mls qos I believe.
>
> Now, if I create a per-port-per-vlan policy map to set the ip-precedence
for devices attached to a port, do I need the "trust ip-precedence" command
within the policy map to change the default behavior of the switch so that
it will map the precedence value to the internal dscp?
>
> mls qos
>
> class-map match-any QOSCLASS
> match access-group 110
> class-map match-all VLANCLASS
> match vlan X
> match class QOSCLASS
> policy-map QOSPOLICY
> class VLANCLASS
> set ip-precedence critical
> trust ip-precedence ???????
> int f0/30
> service-policy in QOSPOLICY
>
> Thanks,
>
> Chris.
>
>
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