Re: 2 Voice vlan questions: 1) Testing the config 2) Dot1p

From: Carlos G Mendioroz (tron@huapi.ba.ar)
Date: Fri Dec 12 2008 - 10:53:44 ARST

Ouch, that hurts... (I'm a very sensitive person, and
that "you are not correct" bounced into my ego shield :)

May I ask how did you got the trace ?
Cause if you are using SPAN, it might be adding tags.

At least for me, monitoring using a hub between phone and switch,
with a 2950 running 12.1(22)EA12, frames from switch to phone are
not tagged when using voice vlan dot1p.

-Carlos

Pavel Bykov @ 12/12/2008 10:23 -0200 dixit:
> Ok. Because this interested me I sniffed the behaviour.
> Carlos, you are not correct - see the sniff output below
> The stup was very simple SW---PHONE---PC
>
> 1. Switch config:
> interface FastEthernet0/13
> switchport access vlan 600
> switchport voice vlan dot1p
> spanning-tree portfast
> end
>
> 2. Switch sends CDP packet to the phone with "VoIP VLAN Reply" field set
> to 0, and "Native VLAN: 600"
>
> 3. IPPhone encapsulates all traffic that it sends with 802.1Q with VlanID=0:
> 802.1Q Virtual LAN, PRI: 3, CFI: 0, ID: 0
> 011. .... .... .... = Priority: 3
> ...0 .... .... .... = CFI: 0
> .... 0000 0000 0000 = ID: 0
> Type: IP (0x0800)
>
> therefore, it can use 802.1p inside 802.1Q
> Switch accepts this traffic.
>
> 4. All traffic from PC is being forwarded untagged to the switch
>
> 5. All traffic that is going from switch to the IPPhone, or PC behind
> that IP Phone is TAGGED WTIH VLAN600 (because in this case it's access
> vlan 600)
> 802.1Q Virtual LAN, PRI: 0, CFI: 0, ID: 600
> 000. .... .... .... = Priority: 0
> ...0 .... .... .... = CFI: 0
> .... 0010 0101 1000 = ID: 600
> Type: IP (0x0800)
>
> This is not what I expected at all
>
> So basically:
> IPPhone --> SW = 802.1Q with VLAN ID 0
> PC --> IPPhone --> SW = No 802.1Q tag
> SW --> IPPhone --> PC = 802.1Q tag with VLAN ID 600
> SW --> IPPhone = 802.1Q tag with VLAN ID 600
>
> wow....
>
> On Mon, Dec 8, 2008 at 11:08 PM, Hobbs <deadheadblues@gmail.com
> <mailto:deadheadblues@gmail.com>> wrote:
>
> Thanks Carlos. That's what I was looking for.
>
> On Mon, Dec 8, 2008 at 3:05 PM, Carlos G Mendioroz <tron@huapi.ba.ar
> <mailto:tron@huapi.ba.ar>> wrote:
>
> > Hobbs,
> > VLAN 0 is not a VLAN, is just a filler for the VLAN ID that is not
> being
> > used. The port is an access port, the VLAN is whichever you
> assigned to it.
> >
> > Traffic being sent to the phone is not tagged.
> >
> > -Carlos
> >
> > Hobbs @ 8/12/2008 19:41 -0200 dixit:
> > > Thank you Alexei.
> > >
> > > But how does traffic get TO or FROM this port with vlan 0 tagged?
> > > How does it learn MAC addresses on this vlan? Does it send it
> out all
> > trunk
> > > ports?
> > > "Show interface trunk" does not show vlan 0 as allowed or active...
> > >
> > >
> > > On Mon, Dec 8, 2008 at 2:17 PM, Alexei Monastyrnyi
> <alexeim73@gmail.com <mailto:alexeim73@gmail.com>
> > >wrote:
> > >
> > >> Hobbs,
> > >> as per 3550/3560 configuration guide:
> > >>
> > >> "Instruct the switch port to use 802.1P priority tagging for voice
> > traffic
> > >> and to use the default native VLAN (VLAN 0) to carry all
> traffic. By
> > >> default, the Cisco IP phone forwards the voice traffic with an
> 802.1P
> > >> priority of 5."
> > >>
> > >> HTH
> > >>
> > >> A.
> > >>
> > >>
> > >> Hobbs wrote:
> > >>
> > >>> Disregard the first question...I had a freakin' ACL on R2. So
> the test
> > is
> > >>> GOOD.
> > >>>
> > >>> My question number 2 still remains...
> > >>>
> > >>> thank you,
> > >>>
> > >>>
> > >>> On Mon, Dec 8, 2008 at 2:04 PM, Hobbs <deadheadblues@gmail.com
> <mailto:deadheadblues@gmail.com>> wrote:
> > >>>
> > >>>
> > >>>
> > >>>> Hello my friends,
> > >>>>
> > >>>> I have 2 questions regarding voice vlans:
> > >>>>
> > >>>> 1) Is it possible to test voice vlan by using subinterface
> and dot1q
> > >>>> encapsulation on a router port:
> > >>>>
> > >>>> R1----SW1----SW2----R2
> > >>>>
> > >>>> R1 has a subinterface with "encap dot1q 2".
> > >>>> SW1 has "voice vlan 2" on port to R1.
> > >>>> Link SW1-SW2 is a trunk with all VLANs allowed.
> > >>>> R2 is in vlan 2.
> > >>>>
> > >>>> R1's config:
> > >>>>
> > >>>> interface Ethernet0/0
> > >>>> !
> > >>>> interface Ethernet0/0.2
> > >>>> encapsulation dot1Q 2
> > >>>> ip address 139.1.2.101 <http://139.1.2.101> 255.255.255.0
> <http://255.255.255.0>
> > >>>>
> > >>>> SW1:
> > >>>>
> > >>>> interface FastEthernet0/1
> > >>>> switchport access vlan 11
> > >>>> switchport mode access
> > >>>> switchport voice vlan 2
> > >>>> spanning-tree portfast
> > >>>>
> > >>>> Should R1 be able to ping R2 at 139.1.2.2 <http://139.1.2.2>
> ? As of right now, I am not
> > >>>> able
> > >>>> to. When I debug icmp, packets from R2 reach R1, but packets
> from R1
> > >>>> never
> > >>>> get to R2. Looks like SW1 is not sending packets from the
> voice vlan
> > over
> > >>>> its trunk to SW2.
> > >>>>
> > >>>> 2) What vlan # is used when you configure "switchport voice vlan
> > dot1p"?
> > >>>> How does the switch know when to send traffic TO this port on the
> > voice
> > >>>> vlan.
> > >>>>
> > >>>> thank you,
> > >>>>
> > >>>>
> > >>>
> > >>> Blogs and organic groups at http://www.ccie.net
> > >>>
> > >>>
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> > >
> > >
> > >
> >
> > --
> > Carlos G Mendioroz <tron@huapi.ba.ar <mailto:tron@huapi.ba.ar>>
> LW7 EQI Argentina
>
>
> Blogs and organic groups at http://www.ccie.net
>
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> --
> Pavel Bykov
> ----------------
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-- 
Carlos G Mendioroz  <tron@huapi.ba.ar>  LW7 EQI  Argentina

Blogs and organic groups at http://www.ccie.net

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