From: Alexei Monastyrnyi (alexeim@orcsoftware.com)
Date: Sat Oct 07 2006 - 07:06:11 ART
Hi.
You may find this URL helpful.
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3560/12225see/scg/swvoip.htm
You can check "Cisco IP Phone Data Traffic" section as well as two
examples in the end.
switchport priority extend...
===
Set the priority of data traffic received from the Cisco IP Phone access
port:
*cos* /value/bConfigure the phone to override the priority received from
the PC or the attached device with the specified CoS value. The value is
a number from 0 to 7, with 7 as the highest priority. The default
priority is *cos* 0.
*trust*bConfigure the phone access port to trust the priority received
from the PC or the attached device.
===
So if PC sends an untagged traffic (neither 802.1q nor 802.1p), this IMO
will not affect the data traffic and it proceeds untagged towards switch
port on your Catalyst.
If there are tags in data traffic, the phone will either override them
(con _value_) or leave as is (trust). Cisco says Catalyst will instruct
the phone to do so via CDP.
Second line of defense is "mls qos ... " on interface level. Catalyst
either trusts CoS values "mls qos trusu cos" (this time regardless of
its source) or overrides them all "mls qos cos override". With latter
you can actually say which CoS value should be used to override "mls qos
cos _value_".
To sum up, if we have the following config
mls qos
in fa 0/1
sw priority extend cos 1
mls qos cos 3
mls qos cos override
"sw priority extend ..." will not make any sense, cause Catalyst is to
override whatever value was set by the phone to CoS value 3.
Hm... have just read what is written and found some doubts if it is
clear enough.. :-)
SW2(config-if)#do sh run in fa 0/1
Building configuration...
Current configuration : 104 bytes
!
interface FastEthernet0/1
_ switchport priority extend cos 1
mls qos cos 3
mls qos cos override_
end
SW2(config-if)#do sh int fa 0/1 sw | in Appl
_Appliance trust: 1_
SW2(config-if)#do sh mls qos inter fa 0/1
FastEthernet0/1
trust state: not trusted
trust mode: not trusted
trust enabled flag: ena
_COS override: ena
default COS: 3_
DSCP Mutation Map: Default DSCP Mutation Map
Trust device: none
qos mode: port-based
This URL is also helpful.
http://www.cisco.com/univercd/cc/td/doc/product/lan/cat3560/12225see/scg/swqos.htm#wp1042819
Sections
Configuring the CoS Value for an Interface
Configuring a Trusted Boundary to Ensure Port Security
HTH
A.
Chee Chew Leong wrote:
> As you know the PC connect to the phone is not a trunk port.
>
> The phone will set the CoS value from the PC traffic if we are using
>
> switchport priority extended cos cos_value
>
> If we would to trust the CoS value of the PC traffic by using
>
> switchport priority extended cos trust
>
> My question is how does this phone trust the CoS from the PC as the
> connection between phone and PC is not a trunk. I am a bit blurred on this
> part.
>
>
>
>
>
>
>
>
>
>
>
> "Roberto Fernandez" <rofernandez@us.telefonica.com>
> Sent by: nobody@groupstudy.com
> 09/30/2006 04:51 AM
> Please respond to
> "Roberto Fernandez" <rofernandez@us.telefonica.com>
>
>
> To
> "Tony Paterra" <apaterra@gmail.com>, "Cisco certification"
> <ccielab@groupstudy.com>
> cc
>
> Subject
> RE: switchport priority extend...
>
>
>
>
>
>
> Tony,
>
> It is definitely A.)
>
> Priority extend is an instruction the switch extends to the phone. The
> phone is the one who actually sets de CoS (anyone correct me if I'm
> wrong)
>
>
> Best Regards,
> Roberto
>
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Tony Paterra
> Sent: Friday, September 29, 2006 3:56 PM
> To: Cisco certification
> Subject: switchport priority extend...
>
> From reading the DocCD I'm not clear on what this command does...
>
> A.) It either trusts or overrides all traffic sent from a PC
> connected to the back of an IP Phone
>
> B.) It either trusts or overrides all traffic sent from a device
> connected to a switchport
>
> My gut tells me that it is B.) and all traffic entering that port (be
> it from an IP Phone or a PC) will be re-tagged or trusted.
>
> Thoughts?
>
> Thanks,
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