DHCP Relay & Option 82

Alan Bryant alan at gtekcommunications.com
Tue Aug 24 22:29:15 UTC 2010

Hello List. This is my first time posting here. I'm not real familiar
with DHCP setups beyond the basic one subnet & one pool design, so I'm
asking for some assistance with my current project.

We currently have a flat network that we are redesigning into a routed
network. We would prefer to have only one DHCP server and a failover,
so we are looking into the DHCP Relay & Option 82 configuration.

I have built a test configuration, however it is not working like I
had expected it to. Here is my config:

ddns-update-style none;
option domain-name "domain.com";
option domain-name-servers,;
default-lease-time 300;
max-lease-time 7200;
log-facility local7;
stash-agent-options true;

shared-network "Tower1" {
 subnet netmask {
  option broadcast-address;
  option routers;
  option subnet-mask;

  class "AP1" {
    match if option agent.circuit-id=0a:00:3e:24:92:78;
    spawn with option agent.remote-id;
    lease limit 1;

  class "AP2" {
    match if option agent.circuit-id=0a:00:3e:92:b6:15;
    spawn with option agent.remote-id;
    lease limit 1;

  pool {
    allow members of "AP1";
    allow members of "AP2";



Once I set our access points up to point to our DHCP server for relay,
I see the request come in on the server with the response "unknown
segment segment".

I did a little searching and found it was because the network that the
request was coming from (A RFC1982 network), did not have a subnet
declaration it would not work. SO I added this to my config:

shared-network "Private" {
 subnet netmask {

Once I added that, the response is now that the subnet does
not have any free leases. I do not want the lease to be given from, but I'm not sure what to do at this point. Any
pointers or advice would be greatly appreciated.

Alan Bryant | Systems Administrator
Gtek Computers & Wireless, LLC.
alan at gtekcommunications.com | www.gtek.biz
O 361-777-1400 | F 361-777-1405

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