From: Pavel Bykov (slidersv@gmail.com)
Date: Fri Dec 12 2008 - 10:23:49 ARST
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> 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>
> 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
> > >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>
> 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 139.1.2.101 255.255.255.0
> > >>>>
> > >>>> 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 ? 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
> > >>>
> > >>>
> _______________________________________________________________________
> > >>> Subscription information may be found at:
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> > >
> > >
> > > Blogs and organic groups at http://www.ccie.net
> > >
> > > _______________________________________________________________________
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> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> >
> > --
> > Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>
-- Pavel Bykov ---------------- Don't forget to help stopping the braindumps, use of which reduces value of your certifications. Sign the petition at http://www.stopbraindumps.com/Blogs and organic groups at http://www.ccie.net
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