Missing option-82 log if "no free leases"

Henrik Sterndorff Jessen hsj at mvb.dk
Tue May 29 19:14:35 UTC 2007


I am using dhcp to dish out fixed addresses to users. All users are
connected to cisco switch ports that act as a relay and therefore add
option-82 information to the dhcp query. I don't know the mac addresses
of the users. 

I am assigning a fixed address to each user using a pool of 1 ip address
(see code below). This gives me the problem, that there are "no free
leases" if the user changes hardware. This is a well known problem that
has been discussed extensively on this list.

I would like to at least see from the dhcp log the option-82 attributes
that have been "dropped" by the server. By I only get a 

"DHCPDISCOVER from 00:0d:da:01:0d:dd via network 10.0.0/24: no
free leases"

And no more log from that mac address. I get log entries from all
addresses that are offered by the server.

The configuration is:

class "myClass" { match if (substring ((option agent.circuit-id),4,2) =
09:02); }

subnet netmask {
	option routers;
	pool { allow members of "myClass"; range; }

## Logging:
if exists agent.circuit-id
        set ClientMAC =  binary-to-ascii (16, 8, ":", substring
(hardware, 1, 6));
        set Vlan = binary-to-ascii (10, 16, "", substring( option
agent.circuit-id, 2, 2));
        set SwitchMac = binary-to-ascii(16, 8, ":", substring( option
agent.remote-id, 2, 6));
        set LeasedIP = binary-to-ascii (10, 8, ".", leased-address);
        set SwitchSlot = binary-to-ascii (10, 8, "", substring ( option
agent.circuit-id, 4,1));
        set SwitchPort = binary-to-ascii (10, 8, "", substring ( option
agent.circuit-id, 5,1));
        log ( info,

I've been troubled by the "no free leases" for a while. And my last
option is writing a script that automatically removes the lease when a
"no free lease" appears in the log. But I need to know the option-82
attributes from the offending client to do that.

Does anyone know a patch to dhcpd that ignores the "hardware" part in
the lease when assigning IP's from a pool? This will of cause also solve
the problem. And yes - I know this is against the RFC's :)

Please help - or I'll have to move to Cisco's CNR :) 


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