From: Eli Kosharovsky (eli_kosh@netvision.net.il)
Date: Mon Jan 15 2007 - 18:13:40 ART
Hi,
After spending the last day, trying to understand how Classification&Marking
on 3550&3560 switches work, I still miss some peaces in the puzzle, if
someone could help a bit this would be highly appreciated:
From what I could understand DSCP-mutation maps are applied at ingress
traffic in the case of 3550 ( 10/100 ports) are shared in groups of ports
1-12 13-24. But you can also achieve the same effect of remarking packets
using the MQC:
Class EF
match ip dscp 46
!
Policy-map in
Class ef
set ip dscp 0
!
Interface fa0/1
Mls qos trust dscp
Service policy input in
The configuration displayed above supposed to mark down EF packets to DSCP
0. this is done in a per port configuration and will not influence fa0/2 for
instance.
The same configuration using DSCP-mutation will look like this:
mls qos map dscp-mutation Prec0 46 to 0
!
Interface fa0/1
Mls qos trust dscp
mls qos dscp-mutation Prec0
But in this case this configuration will be applied to ports 1-12. Which
will make this method much less flexible.
What is the deal, is it really the same, or there differences I am not aware
off.
==========
The second thing I cant figure out is at which point the remarking takes
place ingress or egress. On a router I am completely flexible, I can do
pretty much everything on every port, but seems with switches this is not
the case, If I understand correctly most of the manipulation of the packet
is done at ingress, the egress takes care of queuing.
Meaning all the marking has to be done at ingress - is that really so ?
==========
That's it for now,
Thx in advance for you help
Eli
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