From: Reisner, Tim (TR126568@exchange.DAYTONOH.NCR.com)
Date: Thu Sep 04 2003 - 19:18:23 GMT-3
FYI:
The Cisco Press book "Cisco Field Manual: Catalyst Switch Configuration"
ISBN: 1-58705-043-9
If you can get your hands on one - Section 14-1 explains all of this in
great detail.
Regards,
Tim Reisner
CCIE #10418
-----Original Message-----
From: boby2kusa@hotmail.com [mailto:boby2kusa@hotmail.com]
Sent: Thursday, September 04, 2003 4:06 PM
To: ccie2be; Group Study
Subject: Re: 3550 to IP Phone
No problem. The switch will know since it will not have a dot1p and since
ther eis no dot1p there will be no vlan tag, so if the port is configured
for vlan 10 access it will assume the ubtagged packet is a vlan 10 traffic.
The CDP between the switch and the IP phone will determine whether and tell
the IP phone what is the voice vlan. Remember there is voice vlan under the
interface. The IP phone does not know initially what vlan is the voice
vlan. If you have an IP phone (7960) press setting and then 3 for network
confiugrationa dn then item 19 you'll see Operational vlan this is the vlan
information on that CDP that the switch sent to the Ip phone, in a nutshell.
The tagging happens because of the CDP that this two device understand. If
you connect a non-cisco IP Phone on this device voice vlan will not work,
you'll have to configure dot1q trunk and will have to specify the native
vlan. I believe on AVAYA Ip phones you can specify the vlan for the voice
there. So, all this tagging happens due to the CDP, there is an algorithm
that determines the voice vlan and whether they would be enacapsulated. So
even, if technically and you can verify this with show commands they are not
trunking but because of CDP they kind of are. Confused yet?
----- Original Message -----
From: "ccie2be" <ccie2be@nyc.rr.com>
To: "Group Study" <ccielab@groupstudy.com>; <boby2kusa@hotmail.com>
Sent: Thursday, September 04, 2003 1:22 PM
Subject: Re: 3550 to IP Phone
> Hey boby,
>
> Thanks for getting back to me. Your response helped me understand
> this stuff much better. But, if you don't mind, something is still
> confusing
me.
>
> You point out that the port is an access port which in this case is in
vlan
> 10 and therefore data traffic isn't tagged or encapsulated in any way
> -
it's
> just a normal frame. Therefore, when the switch receives a frame on
> that port, I assume that it handles it the same way that any normal
> switch
would
> ie it looks at the mac addr, does a table look up and makes a
> forwarding decision.
>
> But, how does the switch know whether the frame is a normal data frame
> or
a
> frame carrying voice? It seems to me, based on what you said, that
> the switch would have to look inside each frame it gets to see whether
> or not there's an 802.1q tag in there after the mac address fields.
>
> Also, the switch would have to tag frames leaving the port carying
> voice traffic destined to the IP Phone unless those frames arrived at
> the switch with the 802.1q tag already inside the frame.
>
> Also, according to the 3550 config guide, by default, "the cos value
> is
not
> trusted for 802.1P or 802.1Q traffic. So, with just the command,
switchport
> voice vlan 110, does the switch overwrite the cos value set by the IP
Phone
> to the default for the port?
>
> Thanks again. dt
>
>
> ----- Original Message -----
> From: <boby2kusa@hotmail.com>
> To: "ccie2be" <ccie2be@nyc.rr.com>; "Group Study"
> <ccielab@groupstudy.com>
> Sent: Thursday, September 04, 2003 1:58 PM
> Subject: Re: 3550 to IP Phone
>
>
> >
> > ----- 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
> > >
> > >
> > >
This archive was generated by hypermail 2.1.4 : Wed Oct 01 2003 - 07:24:23 GMT-3