From: Shawn Yang (syang@bitfone.com)
Date: Tue Sep 16 2003 - 19:42:21 GMT-3
OK. I have read through the previous discussion threads on this
topic,
here let me gather what i have understood.
Basically the port can work under both configs, i.e, trunk port
config
(my way) and access port config (IPE solution). The trunk port
config
is more obvious and intuitive. But how does the second config also
work?
Should an access port discard all tagged packets?
The answer might be that cat3550 is a "twisted" beast, different
from both a traditional switch and a traditional router. In fact,
its software is a blend of IOS and CatOS. And its many features
are halfway between a router and a switch, like Port ACLs, and
Vlan
ACLs, etc.
For voice, when an access port is configured with a voice vlan, it
starts to recognize/accept dot1Q encapped packets, (only for the
voice
vlan, however.) So it is in fact half way between an access port,
and a trunk port. Think of such ports as access ports with limited
trunking capability ----- again, a twisted feature.
And of course, when regarded as a trunk, the port's access vlan
automatically
becomes the native vlan...
Cisco seems to prefer the second config, because it is obviously
much
simpler and more scalable. In Cat3550 config guide they explicitly
tell you to config voice vlan on access ports.
http://127.0.0.1:8080/cc/td/doc/product/lan/c3550/12112cea/3550scg/
swvoip.htm#85659
How does this sound?
Shawn
---------- Original Message ----------------------------------
From: "McClure, Allen" <Allen.McClure@yum.com>
Reply-To: "McClure, Allen" <Allen.McClure@yum.com>
Date: Tue, 16 Sep 2003 17:00:16 -0500
>Perhaps I shouldn't have assumed a PC. With a phone only it uses
CDP to
>figure it out on an access port, correct?
>
>A repost or link to an authoritative explanation would be helpful
for me
>as well. I've been following the list for a long time and never
felt
>like anyone nailed it. I could've easily missed it however.
>
>Allen G. McClure
>CCNP/CCDP/MCSE
>Yum! Brands, Inc.
>Sr. Network Analyst
>allen.mcclure@yum.com
>
>
>
>
>
>-----Original Message-----
>From: McClure, Allen
>Sent: Tuesday, September 16, 2003 4:53 PM
>To: 'Shawn Yang'; ccielab@groupstudy.com
>Subject: RE: Cat3550 voice vlan
>
>
>They're wrong.
>
>I would add native vlan configuration for untagged data (PC)
packets (a
>reasonable assumption), although the requirement doesn't specify
a PC
>connected to the phone.
>
>I'd love to hear more comments on this... I've been wrestling
with the
>"right" way to answer this question for quite some time.
>
>Allen G. McClure
>CCNP/CCDP/MCSE
>Yum! Brands, Inc.
>Sr. Network Analyst
>allen.mcclure@yum.com
>
>
>
>-----Original Message-----
>From: Shawn Yang [mailto:syang@bitfone.com]
>Sent: Tuesday, September 16, 2003 1:22 PM
>To: ccielab@groupstudy.com
>Subject: Cat3550 voice vlan
>
>
>Hi, people,
>
>Here is one question in Ipexpert 4.0, appendix H.
>
>(For Cat3550)
>There is a Cisco 7960 IP phone connected to fa 0/15, configure
the port
>as if the phone will be forwarding its voice traffic with 802.1q
>information. Voice vlan is 100.
>
>My answer:
>
>mls qos
>
>int fa 0/15
> swi trunk encap dot1q
> swi mode trunk
> swi voice vlan 100.
> mls qos trust cos
>
>The solution:
>
>int fa 0/15
> swi mode access
> swi voice vlan 100
>
>I am having problem accepting this solution. Should a voice port
have to
>be a trunk port? Because it has to carry at least two vlans,
voice, and
>data? also "mls qos" is not enabled...
>
>Anyone can help me?
>
>Shawn
>
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