From: Bob Sinclair (bsinclair@netmasterclass.net)
Date: Wed Oct 27 2004 - 16:07:04 GMT-3
Andy,
I think that if you are simply trusting dscp, then the incoming cos does not
matter (there is a cos passthru option, but that aside). In this case, the
outgoing cos on a trunk port will be determined by the dscp-cos map. I
think we are on the same page.
Bob Sinclair
CCIE #10427, CISSP, MCSE
www.netmasterclass.net
----- Original Message -----
From: "Edwards, Andrew M" <andrew.m.edwards@boeing.com>
To: "Bob Sinclair" <bsin@cox.net>; <ccielab@groupstudy.com>
Sent: Wednesday, October 27, 2004 11:59 AM
Subject: RE: 3550 qos dscp mutation map question
> Actually it confirms what I read, it just isn't very clear on the
> DocCD... Go figure.
>
> Basically, what I'm hearing you say, is that with "mls qos trust dscp"
> on an access port, the switch trusts incoming CoS values with an
> untagged getting 0 (unless I change the default). Then, the switch
> writes the DSCP value to the packet according to the cos-to-dscp
> mapping. So technically, we aren't dealing with CoS anymore but DSCP.
>
> So if my host is setup to send CoS 3 then the DSCP will be set to 24.
>
> Similarly, I gather, the same holds true for trusting IP precedence.
>
> And just to make sure I really understand, the same holds true for
> access or trunk ports to other switches within my QoS domain.
>
> Now, if that isn't correct please let me know.
>
> Thanks,
>
> andy
>
> -----Original Message-----
> From: Bob Sinclair [mailto:bsin@cox.net]
> Sent: Tuesday, October 26, 2004 8:10 PM
> To: Edwards, Andrew M; ccielab@groupstudy.com
> Subject: Re: 3550 qos dscp mutation map question
>
>
> Andy,
>
> As you say, if you trust CoS, then any unmarked (untagged) traffic will
> get
> the default CoS (0). When that traffic leaves the switch, it will go
> out
> with the DSCP set according to the cos-dscp map. The default cos-dscp
> map
> is as follows:
>
> CoS ->DSCP
> 0 - 0
> 1 - 8
> 2 - 16
> 3 - 24
> 4 - 32
> 5 - 40
> 6 - 48
> 7 - 56
>
> So, if it comes in with cos 5, it will go out with DSCP marked to 40, by
>
> default. The Auto-QoS feature changes this map so that cos3 gets mapped
> to
> DSCP 26 (AF31) and cos 5 gets mapped to DSCP 46 (EF). I believe the
> dscp-mutation map assumes dscp is trusted. If you wanted to convert
> incoming DSCP 40 to outgoing DSCP 46 (EF) you might use this map. Not
> sure
> if this relates directly to your question, but hope it helps.
>
> Bob Sinclair
> CCIE #10427, CISSP, MCSE
> www.netmasterclass.net
>
> ----- Original Message -----
> From: "Edwards, Andrew M" <andrew.m.edwards@boeing.com>
> To: <ccielab@groupstudy.com>
> Sent: Tuesday, October 26, 2004 8:15 PM
> Subject: Re: 3550 qos dscp mutation map question
>
>
>>I haven't been able to drum up a clear answer in my mind on this one...
>>
>> If I set a port to trust cos, I know that the default COS (or 0) is
>> applied to unmarked traffic. What I don't know is if the switchport
>> marks the IP packet with the DSCP value to the cos-to-dscp map?
>>
>> Or, is the DSCP mapping just another way the switch could filter/act
>> on the packet?
>>
>> Any help with this is appreciated.
>>
>> andy
>>
>> ______________________________________________________________________
>> _
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Sat Nov 06 2004 - 17:11:53 GMT-3