From: P729 (p729@cox.net)
Date: Mon May 10 2004 - 22:59:30 GMT-3
Yasser,
'switchport priority extend cos 1' is an interesting command. Taken at face
value, it's supposed to be used to "set the CoS for traffic enterng the PC
port in an auxiliary device." (the only "auxiliary device" I know of is a
Cisco IP Phone) This either implies that the PC port in a Cisco IP Phone
supports 802.1p bits in an (extended) Ethernet frame or it does the same
thing as setting the default CoS on the port for untagged frames (or both?).
CoS is only available in tagged frames, so f0/4 either needs to be trunking
and tagging frames for VLAN 4 (with corresponding support and configuration
on the server's NIC) or the port needs to be setup with a default CoS of 4
so untagged frames entering that port will be treated as such--otherwise a
default CoS of 0 will be used for the untagged frames. If they had said the
server was setting ToS or DSCP or Precedence, then you could trust those
values and then CoS would get mapped and set according to an internal table
or polcy-map. If the frame with CoS set subsequently leaves the switch on a
trunk port, CoS will be preserved and indicated. If it leaves on an untagged
port, it's stripped.
So to answer your 2nd question, the switches would need to be trunked
together and CoS trusted on those trunk ports to "maintain" CoS from
switch-to-switch.
On port f0/8, untagged frames will be treated internally with CoS 1 and as
above, if the frame with CoS set subsequently leaves the switch on a trunk
port, CoS will be preserved and indicated. If it leaves on an untagged port,
it's stripped. If port f0/8 goes into trunking mode, incoming CoS will be
overridden and set to 1.
Regards,
Mas Kato
https://ecardfile.com/id/mkato
----- Original Message -----
From: "Yasser Aly" <blackyeyes00@hotmail.com>
To: <ccielab@groupstudy.com>
Sent: Monday, May 10, 2004 2:38 PM
Subject: End-to-End Switch QoS
> Hello,
>
> Scenario is as follows: VLAN 4 is configured on many ports on the
switch.
> One of the ports is connected to a server providing multicast feeds with a
> CoS value of 4.
>
> Required:
>
> 1) Maintain multicast feed CoS value received at this port as it enters
the
> switch block.
>
> 2) Other ports that belongs to VLAN 4 should be marked with a CoS value of
1
> to avoid getting any better treatment.
>
> Solution Provided:
> ---------------
> mls qos
> !
> int f0/4 ( Where the server is connected )
> mls qos trust cos
> !
> int f0/8 ( Other port belongs to VLAN 4 )
> mls qos cos 1
> mls qos cos override
> -----------------
>
> My questions:
>
> 1) Will there be a difference if I used switchport priority extend cos 1
> instead of using mls qos cos 1 + mls qos cos override on other
ports
> that belongs to this VLAN other than the server port ?
>
> 2) If the scenario has 2 switches and this VLAN has ports on both
switches,
> will there be any configuration needed to the trunk ports to maintain the
> CoS value or I just need to care about the entry point and that's it ?
What
> are the guarantees that the CoS values will be maintained between both
> switches ?
>
> 3) Finally, on the port having the server. Is it possible to assign two
> differnt CoS values on the same port ( One for the mcast feed, and other
for
> the rest of traffic ) ?
>
> Your feedback is highly appreciated.
>
> Yasser
>
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