From: Antonio Soares (amsoares@netcabo.pt)
Date: Fri Jan 26 2007 - 10:42:01 ART
Hello GS,
May I have some comments about this ? I would like to be sure about the
options we have when configuring voice vlan and associated QoS.
Thanks,
Antonio
-----Original Message-----
From: Antonio Soares [mailto:amsoares@netcabo.pt]
Sent: terga-feira, 23 de Janeiro de 2007 23:40
To: 'ccielab@groupstudy.com'
Subject: Voice Vlan, Associated QoS Options and CCIE Level Task
Hello GS,
After failing my first attempt on the ccie lab in 5-sep-2006, i decided to
go back to the basics and to go deeper in the topics. These last days i've
been working on the Voice Vlan topic and i would like to have your opinion
about some conclusions i have:
1) When you have an IP Phone connected to a switch, you may not configure
the port as a trunk. It works but Cisco says that Voice Vlan in only
supported on access ports. Is this correct ?
2) So if the previous is correct, and if we are faced with this type of
setup in the lab, we may leave the default mode (switchport mode dynamic
desirable in the 3550's or switchport mode dynamic auto in the 3560's) or
statically configure the port as an access port (switchport mode access).
3) Then we have 5 options when configuring the Voice Vlan feature:
A) Data traffic untagged in and out, Voice traffic tagged in and out with
VLAN ID=200
interface GigabitEthernet0/7
switchport access vlan 100
switchport voice vlan 200
B) Data traffic untagged in and out, Voice traffic tagged in and out with
VLAN ID=100
interface GigabitEthernet0/7
switchport access vlan 100
switchport voice vlan 100
C) Data traffic untagged in and out, Voice traffic untagged out, tagged in
with VLAN ID=0
interface GigabitEthernet0/7
switchport access vlan 100
switchport voice vlan dot1p
D) Data traffic untagged in and out, Voice traffic untagged in and out
interface GigabitEthernet0/7
switchport access vlan 100
switchport voice vlan none
E) Data traffic untagged in and out, Voice traffic untagged in and out
interface GigabitEthernet0/7
switchport access vlan 100
switchport voice vlan untagged
Do we have any other options ? Regarding the taggings, my conclusions are
based on sniffer traces.
4) The option "switchport priority extend {cos value | trust}" only makes
sense when the device attached to the IP Phone sends tagged frames, either
in 802.1Q, or in 802.1p formats, which is usually not true. And 802.1p is
the same as 802.1Q, the only difference being the Vlan tag=0.
5) Now it comes into play the several QoS options we have.
A) If we want to set the CoS for untagged frames we need:
mls qos
interface GigabitEthernet0/7
mls qos trust qos
mls qos cos cos_value
B) If we want to set the CoS for untagged and tagged frames we need:
mls qos
interface GigabitEthernet0/7
mls qos trust qos
mls qos cos cos_value
mls qos cos override
I'm not sure about this one. Do we really need to trust first then apply the
CoS we want ? Is it possible to set different values for the tagged and
untagged frames ?
6) Finally, a ccie level question related to this topic:
Configure Voice Vlan 200 and Data Vlan 100. The IP Phone will use 802.1Q
encapsulation. Don't trust the Voice Traffic Cos received from the IP Phone
and mark it with CoS=1.
My solution would be:
mls qos
interface GigabitEthernet0/7
! May leave default port more or statically configure as access
switchport mode access
! Assign Data Vlan
switchport access vlan 100
! Assign Voice Vlan. It will use 802.1Q encapsulation with tag=200
switchport voice vlan 200
! We are changing CoS so we need to trust first
mls qos trust qos
! Tagged and untagged traffic will have CoS=2
mls qos cos 2
! Override CoS already assigned by the IP Phone since we have 802.1Q frames
arriving to the Switch
mls qos cos override
Thanks.
Antonio
This archive was generated by hypermail 2.1.4 : Thu Feb 08 2007 - 23:46:57 ART