From: Sami (sy1977@gmail.com)
Date: Thu Jun 15 2006 - 18:42:25 ART
Thanks Roberto for nice explanation. Keep it up !!!
On 6/15/06, Kay D <krsna83@gmail.com> wrote:
>
> 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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