When plugging a IP phone into a network port, how does it know to go to the voice VLAN? 2

[SurferdudeHB]

I'm a bit confused on how a IP phone registers and obtains its IP address from the DHCP server.
I understand the 242 DHCP string scope tells the phone which gatekeeper, file server, directory and voice vlan. But how does the phone on its initial boot up knows where to go after it connects to the DHCP server. How does the DHCP server know it's a IP phone and not a PC or laptop?

 

[mattKnight]

There should be an option 242 on the data scope that tells the phone to use a different vlan

Take Care

Matt
I have always wished that my computer would be as easy to use as my telephone.
My wish has come true. I no longer know how to use my telephone.

 

[SurferdudeHB]

Hi Matt,

But how does the DHCP server know it's a phone registering and therefore provides the voice vlan info to the phone?

 

[kyle555]

242 is a vendor specific option for Avaya. DHCP would send 242:L2QVLAN=100 for VLAN 100 to everything. It's just that only Avaya 9600/1600 phones look at that option and care to start tagging their frames as VLAN 100.

 

[dialtonebone]

The DHCP server doesn't really know it is a phone or laptop (it could surmise it based upon MAC + OUI lookup) -- it just knows a device requested a bunch of specific options and responds with them. In the event of an Avaya phone, it requests Option 242 to get all this data. The phone boots up on data VLAN, gets a message from option 242 saying "Switch to this other VLAN", then the phone starts again on the new VLAN and sends the same request. This time around Option 242 now has all the data needed to get to a PBX and/or fileserver for settings.

 

[mattKnight]

Technically the host does not request an options. The dhcp server receives a request for an up and sends all options. The host then decides which options are relevant to it. That is every host gets all the options set on the scope...

Take Care

Matt
I have always wished that my computer would be as easy to use as my telephone.
My wish has come true. I no longer know how to use my telephone.

 

[SurferdudeHB]

Is the request for Option 242 hardcoded on the Avaya phone?

 

[kyle555]

Yes. The phone is designed to look at option 242 to learn the voice vlan - or LLDP

 

[gwebster]

9600-series can use DHCP Options other than 242. This is set via the SSON setting in the CRAFT menu. With the latest software, they can also use DHCP Option 43 for vendor-specific options. Have a look at

http://support.avaya.com/css/P8/documents/101009361.

 

[dialtonebone]

@mattKnight -- my lab network has option 242 administered, but when I ran wireshark on a release/renew it did not get offered the custom option.

 

[SurferdudeHB]

Thank you all.

 

[mattKnight]

>@mattKnight -- my lab network has option 242 administered, but when I ran wireshark on a release/renew it did not get offered the custom option

Yep, You're correct!

I looked it up and the host actually requests the scope options that it are relevant to it in a DHCP INFORM request.


Thats what I get for spouting off, without checking!

Take Care

Matt
I have always wished that my computer would be as easy to use as my telephone.
My wish has come true. I no longer know how to use my telephone.

 

[SRamjattan]

When you go into the craft menu of the IP phone, there's a option in there that you can tell it what option string to look for.
The setting is SIG or SSON. By default on 96xxand 96x1, it default to 242. This is what's presented to the dhcp server. DHCP server then present the 242 string to the IP phone

Sivan