From: Bob Sinclair (bsin@cox.net)
Date: Wed Sep 08 2004 - 19:32:55 GMT-3
Tom,
The 2950 command reference for 12.1(20)EA2, reads as follows for the command
mls qos trust:
Defaults
The port is not trusted.
Pass-through mode is disabled.
Trusted boundary is disabled.
If no keyword is specified and the switch is running the EI, the default is
dscp.
see link:
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat2950/12120ea2/2950cr/index.htm
This would tell me that, in this version, a 2950 will remark DSCP EF to DSCP
zero BY DEFAULT. This is UNLIKE the 3550, which has mls qos disabled by
default and passes through DSCP. I would suggest you check out the
references for the precise version of IOS you are running. In addition,
check it out in the lab if you can.
BTW, is it really an "XL"? I hope we are talking about the same switch!
HTH,
Bob Sinclair
CCIE #10427, CISSP, MCSE
www.netmasterclass.net
----- Original Message -----
From: "Tom Rogers" <cccie71@yahoo.com>
To: "Scott Morris" <swm@emanon.com>; <ccielab@groupstudy.com>
Sent: Wednesday, September 08, 2004 4:39 PM
Subject: RE: DSCP on router
> Scott,
>
> What I meant was DSCP set to EF, sorry for the wording. So if the voice
device is sending packets set to EF to the 2950XL switches, is the swich
going to remark it to 0 or honor that value and send it to the router? Will
router see those packets marked? Or Do I need to remark it or do some sort
of trust ?
> Thanks in advance
> Tom
>
> Scott Morris <swm@emanon.com> wrote:
> First, I think you mean IP Precedence of 5. :) In DSCP terms, setting it
> to 5 is still IP Prec 0 in the compatibility listing, which won't do much
> for you!
>
> Your switch will rearrange the COS value, which depending on other hops at
> Layer 2 may re-write the IP header TOS field, but by default, the IP
header
> remains untouched and un-looked-at. (Sure, that's a word, ask George W.)
>
>
> Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, CISSP,
> JNCIP, et al.
> IPExpert CCIE Program Manager
> IPExpert Sr. Technical Instructor
> swm@emanon.com/smorris@ipexpert.net
> http://www.ipexpert.net
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Tom
> Rogers
> Sent: Wednesday, September 08, 2004 1:34 PM
> To: ccielab@groupstudy.com
> Subject: DSCP on router
>
> Hi group,
>
> I have a question regarding packet marked as DSCP of 5 for voice.
>
> If a voice device is attached to a switchA and switchA is connected to the
> RouterA. And there is no configuraration done on the the switchA and
RouterA
> and the Voice device is sending packets marked as DSCP of 5,
>
> Q) Is RouterA going to see those packets as DSCP 5 or they will be
remarked
> to 0 ? (Switch A is regular 2950XL switch with no QoS)
>
> Thanx in advance.
>
> Tom
>
>
>
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