From: boby2kusa@hotmail.com
Date: Thu Sep 04 2003 - 14:58:38 GMT-3
----- Original Message -----
From: "ccie2be" <ccie2be@nyc.rr.com>
To: "Group Study" <ccielab@groupstudy.com>
Sent: Thursday, September 04, 2003 8:35 AM
Subject: 3550 to IP Phone
> Hi all,
>
> I'm trying to understand what's going on between the 3550 and the IP Phone
> under different circumstances, but the more I look into this, the more
> confused I get.
>
> Consider this example from the Cisco DQOS book, page 737 where a 3550 is
> connected to an IP Phone which is connected to PC. It says, "Assuming
that
> the voice vlan has been configured for 110 and the data vlan has been
> configured for 10, Example 10-34 shows the configurations necessary on the
> 3550."
>
> 10-34
> CatIOS (config)# interface FastEthernet0/11
> CatIOS (config)# switchport access vlan 10
> CatIOS (config)# switchport voice vlan 110
> CatIOS (config)# spanning-tree portfast
>
>
> Then the book says, (I paraphrase) this configures a 802.1Q trunk from the
IP
> phone which tags voice traffic in vlan 110 and untagged traffic in vlan
10.
>
> Question 1: Does the switchport voice vlan # command automatically create
the
> 802.1q trunk? Or, did that have to be configured previously but that's
shown
> in this example?
It says FROM the IP Phone, there is no mention that the port will do
trunking, technically the IP Phone will use Dot1p for CoS and vlan tag. The
Ip Phones and the switch uses the CDP to id the voice vlan. The IP Phone
will not encapsulate the data packet therefore when the data packet reaches
the port it will be assume by the switch that it's origin is from vlan 10
since the port is an access port for vlan 10.
>
> Question 2: How can a port be both a trunk port and an access port at the
> same time? Aren't they mutually exclusive?
It is not trunking - show int fa 0/1, you will see it's not trunking,
however, it will know there is voice vlan and access vlan.
>
> Question 3: Isn't untagged traffic, by definition or by default, in the
> native vlan? And, isn't the native vlan vlan 1 by default?
True but the native vlan concept is only when the port is trunking.
And, therefore,
> traffic in vlan 10 is tagged as vlan 10 unless vlan 10 was previously
> configured as the native vlan? Does it matter whether or not the data
traffic
> is carried in the native vlan?
The port is an access port that belongs to vlan 10.
>
> Question 4: Would the above config work whether or not the native vlan
was
> manually set to 10?
Yep, since it is not trunking it will not even care for the Native vlan.
>
> Question 5: Does any particular configuration need to be done on the IP
Phone
> to make it compatible with the above configuration on the switch? If so,
> what?
The IP PHone uses CDP to id the voice vlan. No configuration needed other
than what you configure on that CM such as extension, VM received LED,
forwarding, etc.
>
> As you can tell from all the questions above, I'm really confused about
all
> this. I'm not even sure if I'm asking all the right questions, so I would
be
> extremely appreciative to anyone who could clear out all the fog from my
brain
> on this topic.
>
> Thanks in advance, dt
>
>
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