LLDP Question

[pakman]

Hello,

I'm trying to understand more about the phone boot up process and vlans. When I watch a phone boot up it goes through 802.1x, LLDP, DHCP, Vlan 100, Option 125 and Minet before starting up.

In our DHCP options we don't have vlan info set and so I'm wondering how exactly LLDP plays a role in the phone getting on the voice vlan? Ultimately, when troubleshooting some phones I show the phone registering in both our data vlan and voice vlan and I don't get how that's possible.

Thanks,

[johnp]

LLDP can set priority and vlan. Most phones can take this and move to the assigned vlan. As you see this happens before the DHCP request. In your case they move to vlan 100 and are provided an address and other options contained in the 125 string.

[acejavelin]

LLDP may or may not have anything to do with this, the phones could be moving to the desired VLAN in other ways such as Cisco SmartPort as well. The fact they seem to be on two vlans at once is odd... I would start at the switch level and look at the ports and they uplinks to other switches. Hard to say from the given information what the cause could be.

[VinceWhirlwind]

LLDP is a protocol that runs on various networking devices. It sends regular advertisements out ethernet interfaces which a neighbouring device also running LLDP will receive. These advertisements contain a few details about the device sending it.
For the phones running LLDP, the thing they are looking fo rin the LLDP advertisements from the switch they are connected to is a line to the effect, "VLAN20 VOICE".
The phone sees this and configures its LAN-facing interface to be tagged in VLAN20.
Then, the phone can send a DHCP request out VLAN20 and get assigned an IP address in the Voice VLAN subnet.
 
Alternatively, if there is no LLDP, the phone will not learn any VLAN ID, so it will send a DHCP request out its LAN-facing interface within untagged frames. This request will go to the Data VLAN DHCP scope, and the phone will be assigned an IP address within the Data subnet. The DHCP offer will contain Option125, including the correct VLAN ID for the Voice VLAN. The phone will assign the Voice VLAN ID to itself and add it as a tagged VLAN to its LAN-facing interface, and then reboot itself, coming up in the Voice VLAN, and then sending a DHCP request off into the Voice VLAN so it can get a Voice VLAN subnet IP address.

If you're seeing the phone in both scopes on the DHCP server, it could be either the second process is what's happening, or your DHCP server is patched to a switchport that is misconfigured with multiple VLANs assigned to it.

[iboyd]

LLDP is cool to get you up and running when your in a time crunch, but if you have time, configure you switchports so you know what is where.  That also gives you a good time to document your switchports, so when things go belly up, you have a reference point of what should be where. 

-Ian

[v2win]

LLDP is cool to get you up and running when your in a time crunch, but if you have time, configure you switchports so you know what is where.  That also gives you a good time to document your switchports, so when things go belly up, you have a reference point of what should be where. 

-Ian

pffffftttt documentation.... if it was hard to put in it should be hard to troubleshoot.

[VinceWhirlwind]

LLDP is cool to get you up and running when your in a time crunch, but if you have time, configure you switchports so you know what is where.  That also gives you a good time to document your switchports, so when things go belly up, you have a reference point of what should be where. 

-Ian

I think you are thinking of Cisco VTP. Don't use Cisco VTP.
 
LLDP doesn't configure your switchports - it configures your phone. You don't want to manually configure every single handset to tell it what its Voice VLAN is. You can let DHCP configure your phone, but the phone will need to boot up twice to get onto the Voice VLAN if you do it that way, so LLDP is better.

[iboyd]

Virtual Trunking Protocol (VTP) shouldn't be in the discussion  .  I know LLDP deals with Network Discovery, along the same lines of CDP. I may have described VTP, my point being is that I do not want either a Cisco Protocol (CDP) or an open-source Protocol (LLDP) telling my VoIP device which vLAN is which.

and v2win: it helps also when people move ports thinking they can without calling the Helpdesk first  , that way when the port dies, and i can point out that they moved ports without telling IT they get very bashful.  I have sites in Utah, Idaho, etc, I can't just walk over and move the port back.

-Ian

[pakman]

Thanks for all the responses.

I have a couple of follow up questions which will hopefully solidify all this for me.

VinceWhirlwind what you posted makes since to me but I also was reading something about how Cisco phones boot up and the bold text is what I read. If this isn't the same for Mitel and it's how you described it with the phone waiting around for an LLDP message from the switch to tell it that it's voice is there any documentation out there on this? Not that I'm questioning your knowledge I just like to learn and understand things to the best of my ability. I have not come across any really good articles explaining LLDP and VOICE.

Thanks, 

Do Mitel phones have a small switch in them andunderstand 802.1Q, when the phone sends the first packet to the switch the port knows if it's configured with a voice vlan since the packet was tagged it can then send a LLDP message saying here is your voice vlan? If not, I know the phones have LLDP enabled on them does the phone advertise to the switch here's all my info and btw I'm a phone so put me in the voice vlan? If that's the case what exactly in the LLDP advertisement says I'm a phone?

To iboyd....if you don't use LLDP or CDP I assume you program everything in DHCP then? I use 802.1X with MAB so it doesn't matter to me where end users move devices to just so that my wall jack numbers match my patch panel life is good...

[pakman]

I did do a packet capture with WS and saw that my BIA of my switchport was the source for the LLDP packet so the phone waits for an LLDP packet with the correct vlan info before proceeding like you mention below.

Thanks,

[VinceWhirlwind]

.... does the phone advertise to the switch here's all my info and btw I'm a phone so put me in the voice vlan? If that's the case what exactly in the LLDP advertisement says I'm a phone?

Well, it might depend on the phone, but I see no reason why the phone needs to send any LLDP, it just needs to listen.
The phone needs to be running LLDP, as well as the network switch.
When you connect the phone to the switch, the phone will see LLDP advertisements from the switch.
Those advertisements contain info about the Voice VLAN.
The phone now knows how to tag its voice traffic.
 
But I already explained all this, so not sure what you are asking really.

[pakman]

Since I did the packet capture and verified for myself that the phone receives the LLDP info from the switch no further questions on this.

I do however have another question since were talking about phone boot up process. I ran across this just this morning so its good timing. I found a particular switchport that didn't have 802.1X settings nor was it  setup on the voice vlan. When I looked at the mac table It showed a phone and pc registered. I confirmed the PBX had this phone in the all IP phone inventory and had an IP address from our data side.

I'm wondering how this phone is working since only PBX's hand out DHCP info to our phones and we have a separate DHCP server on our domain controllers for data. I was under the impressing that phones had to have option 125 in order to work properly? I don't have any phone options on the DC related to phones.

Thanks,

[Dogbreath]

I was under the impressing that phones had to have option 125 in order to work properly? I don't have any phone options on the DC related to phones.

If you put a handset in teleworker mode it will work without any DHCP options [it doesn't care the if IP you gave it is an MBG or an MCD if there's no NAT]. I have used this as quick fix a number of times.

[Dogbreath]

Do Mitel phones have a small switch in them andunderstand 802.1Q, ... If that's the case what exactly in the LLDP advertisement says I'm a phone?

Yes, basically a 3-port switch.
The LLDP capabilities field indicates that it's a phone.
If you didn't already know, look at the neighbours table on your switch - you will see the DN of each device. Very handy.

To iboyd....if you don't use LLDP or CDP I assume you program everything in DHCP then?

Yes, or do it manually, but nobody wants to do that!

[johnp]

If you put a handset in teleworker mode it will work without any DHCP options [it doesn't care the if IP you gave it is an MBG or an MCD if there's no NAT]. I have used this as quick fix a number of times.

Wouldn't call it a fix, maybe a work around for a misconfigured network. I too have had to do this and find it is often because the L2 device isn't setup properly or they only have L1