From: Kay D (krsna83@gmail.com)
Date: Thu Jun 15 2006 - 07:30:59 ART
Hi ,
I carried out a test on an alcatel ip phone ,which wanted me to use
the sw mode trunk .
,,,again its not the same with other phones too .
But over configuring "sw mode trunk " does not cause an issue
,,,,,i guess :)
Kay D
On 6/15/06, Shanky <shankyz@gmail.com> wrote:
>
> Thanks Roberto, for taking out your time and explaining it so well.
>
> Shanky
>
> On 6/14/06, Roberto Fernandez <rofernandez@us.telefonica.com> wrote:
> >
> > Sami,
> >
> > Let break it down to the components you will find then all the
> > combinations. Here we have two things:
> >
> > 1- The actual indication to the switch of the presence of a "special"
> > VLAN (the voice VLAN)
> > 2- The QoS treatment the switch will give to that port (both for the
> > data and the access VLANs)
> >
> > The simplest way for a switch port to work is having a VLAN configured
> > and dumb host connected to it. In this case the switch's default
> > behavior would be trying to convert the port to a trunk, issuing a few
> > DTP (Dynamic Trunking Protocol) frames. But as said before, the host is
> > dumb and doesn't care for DTP. The switch quickly gives up and the port
> > becomes "dynamic access" in the mean time the switch also tries CDP
> > hoping to find a Cisco cousin at the other side.
> >
> > Let bring now a phone and connect it to that switchport. Down to the
> > basics a phone could be no different to the dumb host, but the phones we
> > care about are a little bit more; must phones are small switches. And if
> > you look at them you will see, they usually have two Ethernet ports: One
> > for the uplink and one to connect a device (commonly the PC). From now
> > on we will speak fo phones that can talk to the switch, (Cisco phones of
> > course)
> >
> > When you connect one of those Cisco phones to the switch, you will
> > clearly have now two devices originating traffic. The phone itself,
> > originating voice traffic; and the PC originating data traffic. Having
> > two kinds of traffic usually leads to the requirement of differentiating
> > them and treating them differently through some QoS technology. When the
> > switch recognizes the Cisco phone the will engage in some exchange of
> > configurations.
> >
> > Summarizing, we have now:
> >
> > 1- A fairly smart Layer3 Switch
> > 2- A no so dumb IP phone which in turn connects another device
> > 3- The need to differentiate at the switch, traffics originating on the
> > phone and the PC.
> >
> > Well, let start recognizing which traffic belongs to the phone and which
> > to the PC. Cisco has two methods
> >
> > a) 802.1q
> > b) 802.1p
> >
> > a) The 802.1q is really straight forward, when you issue the "switchport
> > voice vlan XX" command it is actually a command aimed to the phone. The
> > switch is telling to the phone: "tag the voice traffic you are sending
> > with XX 802.1q VLAN header" the phone will follow the instruction and by
> > default will assign also a CoS of 5 to those frames. The traffic coming
> > from the PC will come untagged and the switch will need to know which
> > VLAN assign to it, well this is the "switchport access vlan YY"
> >
> > b) The 802.1p works in principle very similar "switchport voice vlan
> > dot1p" is similarly an instruction to the phone, and the default values
> > are the same (data on VLAN 0 and Cos of 5 for the 802.1p
> >
> >
> > Now let add the QoS options, remember we have two traffics already
> > recognized and the configuration until now is as follow (using 802.1q):
> >
> > Interface Fastethernet 0/1
> > switchport access vlan XX
> > switchport voice vlan YY
> >
> > Well, by default the switch won't care about what is coming and will
> > apply assume a CoS of 0 of everything coming into the port be it tagged
> > or not, this command "mls qos trust qos" will trust what the phone is
> > applying to tagged frames (this is the same for 802.1q or 802.1p kind of
> > tags. To be able to use mls qos commands at the interface we need to
> > enable it globally also. We have now:
> >
> > !
> > mls qos
> > !
> > Interface Fastethernet 0/1
> > switchport access vlan XX
> > switchport voice vlan YY
> > mls qos trust qos
> > !
> >
> > and the switch now cares about what the phone is tagging as voice. If we
> > do not care about the PC hanging from the phone, we could are done; but
> > we do... let say this is an important PC a VP's PC and we want to give
> > him something better than the default CoS of 0, well we can change the
> > default CoS of the switchport:
> >
> > mls qos cos 3
> >
> > now let say the VP is smart enough to make his PC mark traffic as CoS 5,
> > but 5 is only voice and maybe the CEO... then you can instruct your
> > phone to override his marks
> >
> > switchport priority extend cos 3
> >
> > and no matter what he does his data will come as Cos 3
> >
> > or it could be the CEO, then you let them mark himself as he wants
> >
> > switchport priority extend trust
> >
> > So depending the treatment you want to give to the PC you can finish
> > your configuration with a combination of changing the default CoS for
> > the port and a remote trust of override option for the PC port. Let say
> > it is the CEO and we trust his marks, but if he forgets to mark, we will
> > give him CoS 3.
> >
> > !
> > mls qos
> > !
> > Interface Fastethernet 0/1
> > switchport access vlan XX
> > switchport voice vlan YY
> > mls qos trust qos
> > mls qos cos 3
> > switchport priority extend trust
> > !
> >
> > Well, this is a little bit long, and doesn't cover other options fur
> > trusting (DSCP, IP-Precedence, Cisco-Phone) but HTH with the basics,
> > going through the configuration guide and then the command reference
> > (for more options) will give you the rest.
> >
> > http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12225see/scg/s
> > wvoip.htm#wp1034347
> >
> >
> > http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12225see/cr/cl
> > i1.htm#wp1862788
> >
> >
> > Best Regards,
> > Roberto
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > Sami
> > Sent: Wednesday, June 14, 2006 4:07 AM
> > To: ccielab@groupstudy.com
> > Subject: Voice VLAN
> >
> > Group,
> >
> > Voice VLAN story is really giving me hard time. We have so many experts
> > on
> > this list , can't somebody explain what is the right way of configuring
> > Voice VLAN. I read three different workbooks CCO doc site and each has
> > their own solution.
> >
> > This one from InternetworkExpert,
> >
> > interface FastEthernet0/7
> > switchport access vlan 7
> > switchport voice vlan 10
> > switchport priority extend cos 1
> > mls qos trust cos
> >
> > these guys say since 3550 port is in dynamic mode , switch automatically
> > form a trunk with Cisco Phone and don't require to configure port as a
> > trunk
> > or access mode and no spanning tree portfast.....
> >
> > I know in real life things work in a diffrent way , could some one
> > please
> > calrify which way Cisco expect us to configure Voice VLAN stuff in lab
> > so we
> > don't loose point in tussel of Trunk /Access/Advanced CDP/portfast
> > etc...stuff.
> >
> > Many thanks !!
> >
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