[asterisk-users] Understanding how LLDP works with DHCP [SOLVED]
oza.4h07 at gmail.com
Tue Jan 24 02:36:09 CST 2017
2017-01-19 18:19 GMT+01:00 Jose Flores Galicia <flojose at gmail.com>:
> 2017-01-19 4:09 GMT-06:00 Olivier <oza.4h07 at gmail.com>:
>> For years, I used to configure SIP phone VLAN membership through a DHCP
>> Here are the details:
>> - I dedicate a LAN port on a switch to voice VLAN
>> - somewhere else, I configure a DHCP server to serve LAN addresses within
>> voice VLAN
>> - any other switch port connected to an other DHCP server is explicitely
>> excluded from voice VLAN
>> - new SIP hardphones are first connected to the dedicated voice VLAN
>> port: after several reboots, they get an address within voice VLAN address
>> range and save VLAN tag somewhere within their persistent memory
>> - SIP phones are then moved to an other switch port: as they boots, they
>> request a LAN address using previously received VLAN tag.
>> Now I would like to improve this process using LLDP.
>> I ran a couple of tests in my lab and still have some questions:
>> 1. My lab switch sends within LLDP frames, a list of VLANs. One is named
>> "default" and the other is named "voice".
>> Do LLDP-capable phones look for a specific name to elect the VLAN tag
>> they will later use to build DHCPDISCOVER request or do they look for
>> something else (medPolicy) ?
>> 2. With LLDP, do you still need your DHCP server to embed VLAN membership
>> data within DHCPOFFER or is it a thing of the past ?
>> 3. Have you been successfull with LLDP on a KVM guest networked to an
>> LLDP-enabled switch through a linux bridge (see ) ?
>> Where can I find information regarding the line bellow:
>> echo 16384 > /sys/class/net/<bridge_name>/bridge/group_fwd_mask
>>  https://thenetworkway.wordpress.com/2016/01/04/lldp-traffic-
>> Best regards
>> -- Bandwidth and Colocation Provided by http://www.api-digital.com --
>> Check out the new Asterisk community forum at:
>> New to Asterisk? Start here:
>> asterisk-users mailing list
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> Hi Oliver.
> 1. Actually there are 2 protocols which must be supported on switch and ip
> phone, one is LLDP wich inventories both ways. IP Phone <-> Switch, to
> ellaborate on both devices MIB database with switching/routing/app
> capabilities of their partner; second is the LLDP-MED (Media Endpoint
> Discovery) which is capable of sending L2/L3 settings to devices. These
> settings are in several categories, concerning your question is "Network
> Policy" settings wich will be sent to the ip phone based on their app
> capabilities (LLDP).
> "Network Policy" settings can contain VLAN ID for voice and other ID for
> Data, and other for Video, etc. Once the LLDP-MED "Network Policy" settings
> are received on ip phone, will tag the phone traffic on the specified VLAN,
> On switching capable ip phones (2 or more ethernet interfaces), probably
> will only tag phone traffic, and leave the switched traffic on the access
> So ip phone sends DHCPREQUEST on the VLAN ID set by LLDP-MED.
> 2. DHCP VLAN settings will probably being ignored since most of devices
> will prefer LLDP-MED settings.
> 3. With LLDP enabled on KVM guest, you can obtain information about
> network devices attached, their capabilities, brand, model, etc. I have
> never tried but LLDP-MED supposed only to work on next switch device (Link
> Layer), not a propagation protocol.
> I always have deployed LLDP-MED capable ip phones on a LLDP-MED capable
> network is:
> 1.- Enable LLDP on all access switches so they can advertise and receive
> LLDP information.
> 2.- Configure LLDP-MED on all ports where will be connected ip phones and
> set the correct Network Policy, sending LLDP-MED capable voice devices to
> voice VLAN ID
> 3.- DHCP server exists attached to voice VLAN ID, as LLDP-MED will provide
> same VLAN ID, phone will receive at the first boot their DHCP settings.
> Best Regards.
> -- Bandwidth and Colocation Provided by http://www.api-digital.com --
> Check out the new Asterisk community forum at: https://community.asterisk.
> New to Asterisk? Start here:
> asterisk-users mailing list
> To UNSUBSCRIBE or update options visit:
Combining a Yealink phone with a Ubiquiti switch, and thanks to above
explanation,I could at last have my very first working LLDP experiment !
To sum up things: it seems an LLDP-enabled switch port would send a frame
including an LLDP policy. This LLDP policy (which can be specific to each
port) describe which tag to use to "enter" Voice VLAN.
In turn LLDP-enabled phone would tag its DHCP DISCOVER request with
appropriate VLAN tag value and there is no need to include vendor-specific
VLAN data in DHCP OFFER anymore.
The benefit is that with LLDP, any factory-reset phone can be plugged in
any LLDP-enabled network and get appropriate VLAN config.
Thanks for helping.
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