From: Chris Lewis (chrlewiscsco@gmail.com)
Date: Thu Apr 13 2006 - 10:18:09 GMT-3
Nick,
I posted this before, but pasting it in here will save one of those arduous
searches througuh the archives :)
The following is an exchange between myself and an internal subject matter
expert on this topic. I'm asking the questions, and he is answering in-line.
Hoppe this clears it up. If not, I think the documentation at
http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12225see/scg/swvoip
.htm
is not all that bad.
Chris
What is the "right" way to configure voice vlan on a 3550, I see differing
recommendations. For example in Maurilio Gorito's book, I see the following:
In practice lab 2, configurations are shown for connecting a 7960 that does
trunking, and a 7905 that does not do trunking.
The port connecting to a 7960 is configured for trunking, and the port
connected to the 7905 is not. This is given on p96
3550 config for 7960 phone
int fa0/16
switchport access vlan 2
switchport trunk encapsulation dot1q
switchport trunk native vlan 2
switchport mode trunk
switchport voice vlan 50
no ip address
duplex full
speed 100
spanning-tree portfast
3550 config for 7905 phone
int fa0/17
switchport access vlan 50
no ip address
duplex half
speed 10
The explanation is given as follows:
The 7960 has the capability to trunk to the 3550 as it has an on-board 3
port switch and can separate the voice and data traffic
appropriately.The7905 phone only has 10 base T and needs manual
insertion in to the voice
vlan. Ensure that the port connecting to the 7960 is configured as a trunk
using dot1q and that the native vlan is 2.
*This is an older method of configuring the Voice VLAN (VVLAN) and the
native Data VLAN (DVLAN).*
However, if I search newsgroups, I see lots of recommendations that list the
following:
mls qos
! interface FastEthernet0/7
switchport access vlan 20
switchport voice vlan 10
switchport priority extend cos 0
mls qos trust cos
spanning-tree portfast
*Yes - this is the newer way. The "switchport voice vlan" command was
introduced in 12.1(9)EA1. Basically, it allows the config to be shortened by
a few lines, as it automatically sets up the dot1q trunk (by default), and
assosciates the DVLAN as a native VLAN, etc.*
I guess my main question is if you have a 3550 connected to a 7960 phone,
should the 3550 port be configured for trunking or not? If the answer is
both are valid configurations, are there any differences in operation?
*Both configs will set up the VVLAN/DVLAN via dot1q trunking. It's just an
administrative preference to enter the full set of commands or just
"switchport access vlan" coupled with "switchport voice vlan".*
In maurilio's example, why would the 3550 port be configured both for accees
and trunking?
*Because the port is configured to operate as an access-port for the native
VLAN (the DVLAN); trunking only applies to the VVLAN. Yes, it's a bit
confusing, but that's how they coded it.*
In Maurilio's example, is this analysis correct?
For the 7960 phone to encapsulate in to .1q packets, it needs to know the
vlan ID to use, and you do not configure the 7960. What you do configure is
the 3550 port and that uses CDP to tell the 7960 what the voice vlan number
should be, in this case 50. Now nothing has told the 7960 what vlan header
to encapsulate the data traffic in to, so it does not encapsulate it in to
anything. So if we want to get the non .1q packets coming from the PC
attached to the 7960 phone in to a specific vlan, our only choice is to make
that the native vlan, so the 3550 will say, a hah, a non .1q packet,
therefore it is in the native vlan and off we go.
*This seems about right to me. *
On 4/12/06, Nick Griffin <ngriffin@sio.midco.net> wrote:
>
> Should the "switchport voice vlan dot1p" be used in conjunction with
> this configuration listed below? Whats happens with the priority of
> voice over data in the configuration listed?
>
> Thanks
>
> Chris Lewis wrote:
> > Brad,
> >
> > That used to be the case a long time ago, but configuring the port to be
> a
> > trunk port is not necessary any more if you are connecting to a Cisco IP
> > Phone.
> >
> > The following is a configuration from Larry Letterman from a switchport
> in
> > the Cisco network.
> >
> > interface FastEthernet0/1
> > switchport access vlan 5 >>>data vlan
> > switchport mode access
> > switchport voice vlan 10 >>>>voice vlan
> > no ip address
> > spanning-tree portfast
> >
> >
> > On 4/12/06, Brad Ellis <brad@ccbootcamp.com> wrote:
> >
> >> Are you connecting a phone to the switch port? If so, you'll want to
> >> configure the port for trunking mode, and NOT access mode.
> >>
> >> thanks,
> >> Brad Ellis
> >> CCIE#5796 (R&S / Security)
> >> CCSI#30482
> >> brad@ccbootcamp.com
> >> www.ccbootcamp.com (Cisco Training and Advanced Technology Rental
> Racks)
> >> CCIE Voice Lab Workbook - Now Shipping!
> >>
> >> ----- Original Message -----
> >> From: "Melwani, Manoj J" <melwanim@citigroup.com>
> >> To: "CCIE Group Study (E-mail)" <ccielab@groupstudy.com>
> >> Sent: Wednesday, April 12, 2006 1:52 PM
> >> Subject: Leaving the switchport to dynamic for Voice VLANS or making
> >> itaccess on 3550 [bcc][faked-from]
> >>
> >>
> >> Can some one suggest if we should leave the switchport in dynamic mode
> or
> >> change it to access while configuring Voice VLAN's or it doesnt matter?
> >>
> >> interface FastEthernet0/11
> >> switchport access vlan 5
> >> switchport mode dynamic desirable
> >> switchport voice vlan dot1p
> >> switchport priority extend cos 3
> >> mls qos trust cos
> >> spanning-tree portfast
> >>
> >>
> >> OR
> >>
> >> interface FastEthernet0/11
> >> switchport access vlan 5
> >> switchport mode access
> >> switchport voice vlan dot1p
> >> switchport priority extend cos 3
> >> mls qos trust cos
> >> spanning-tree portfast
> >>
> >>
> >>
> >> thanks,
> >> Manoj.
> >>
> >>
> >>
> >> Manoj J. Melwani
> >> Citigroup - Extranet Network Integration
> >> Phone: (212) 291-3189
> >> Email: melwanim@citigroup.com
> >>
> >> _______________________________________________________________________
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> >>
> >> _______________________________________________________________________
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> >>
> >
> > _______________________________________________________________________
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