From: Victor Cappuccio (cvictor@protokolgroup.com)
Date: Mon Jul 17 2006 - 19:17:43 ART
Hi Thomas,
This is my interpretation of what the Cat 3550 does when MLS QOS is enabled
At the ingress port if is set to trust COS for IP and Non-IP Traffic, it
checks the packet (ptk) to see if it came with a TAG (Cos), if the pkt came
with a TAG it generates the DSCP Value by using the Cos-To-DSCP Maps, if the
pkt did not came with a COs Value, it assignees the default port COS and
generates a DSCP from the COS-DSCP Map
If we configure the switch to Trust IPP for IP Traffic, it would generate
the DSCP based on the IPP in the pkt, by the mapping of IPP-to-DSCP.
if we set the switch to Trust the DSCP, it would assign the same internal
DSCP, that the pkt has, you can optionally configure DSCP-DSCP Mutation.
If the port is configured as default, it would check the COS label and if
the pkt has a cos label it would use the cos of the frame, if not it would
assign the cos configured in the port.
For both 2 it would use the internal COS-DSCP Map.
Something to have in mind is that when you enable QOS MLS in the 3550 you
must disable flowcontrol
Sw1(config)#int range f0/1 - 24
Sw1(config-if-range)#flowcontrol receive off
Anyways there is a warning generated by the switch when you enable QOS
Sw1(config)#mls qos
QoS: ensure flow-control on all interfaces are OFF for proper operation.
To the different mappings u can use
Rack7Sw1#show mls qos maps ?
cos-dscp Show COS to DSCP map
dscp-cos Show DSCP to COS map
dscp-mutation Show dscp-mutation map
dscp-switch-priority Show DSCP to switch priority map
ip-prec-dscp Show IP precedence to DSCP map
policed-dscp Show DSCP to policed mark down DSCP map
| Output modifiers
<cr>
HTH and please correct me if I'm wrong
Victor.
Good luck to both in September, and please sorry my English I know it sucks
:D
-----Mensaje original-----
De: nobody@groupstudy.com [mailto:nobody@groupstudy.com] En nombre de TAM
Enviado el: Lunes, 17 de Julio de 2006 05:32 p.m.
Para: GSCCIEML
Asunto: Summary of 3550 markings
Hi All,
In an effort to get my head around the 3550's QoS features I was
wondering if someone could read and confirm/correct my summary below
regarding the marking of a packet during its time with the 3550, Or
perhaps provide a reference to similar matter.
(assume defaults config unless specified, and by 'Packet' I mean L2/3
frame/packet as appropriate).
<START>
Without mls qos (no concept of trust here):
Packet is sent best-effort.
No marking of packets occur (no change to any Layer2/3 bits within the
packet)
With 'mls qos' enabled and ingress port untrusted:
At ingress the Packet is marked with the default cos value (0,
configurable per port) and default DSCP 0 (not the Internal DSCP value,
but the actual L3 DSCP value of the packet is changed)
At Egress the packet is assigned to wrr queue #1 (default for COS 0 &
1), the packet now has a COS value of 0 and a DSCP value of 0
With 'mls qos' enabled and ingress port trusted:
At egress packet will exit with same incoming value of COS/DSCP/IPP as
it arrived with, i.e.
-if port is trusted for COS, outgoing COS value= incoming COS value
-if port is trusted for IPP, outgoing IPP value= incoming IPP value
-if port is trusted for DSCP, outgoing DSCP value= incoming DSCP value
This is due to the use of the internal DSCP value which allows for the
consistency throughout the packet's lifetime
** think I might be missing something here!
<END>
Thanks in advance,
Thomas.
P.S. First post in Groupstudy! Be lurking silently for months,
thoroughly enjoying the list, makes for excellent reading. Aiming for
Lab in September in Brussels.
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