3550 to IP Phone

From: ccie2be (ccie2be@nyc.rr.com)
Date: Thu Sep 04 2003 - 12:35:53 GMT-3

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?

Question 2: How can a port be both a trunk port and an access port at the
same time? Aren't they mutually exclusive?

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? 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?

Question 4: Would the above config work whether or not the native vlan was
manually set to 10?

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?

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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