DHCP Relay over transit-network

Muenz, Michael m.muenz at spam-fetish.org
Tue Dec 30 13:34:50 UTC 2014

Am 30.12.2014 um 14:20 schrieb Muenz, Michael:
> Am 30.12.2014 um 14:13 schrieb Simon Hobson:
>> Same thing, different names. Check on FW2 that the packets are going 
>> through, and whether there is any reply at all from the server. Then 
>> look at the server logs. And assuming FW2 isn't the default gateway 
>> for the server at that end, check that the server (or the default 
>> router) has a route to the transit network.
> Packets are leaving FW2's internal interface, but no reply. I'm not 
> the dhcp crack, but in the dump I'm missing the Option 82 field. 
> Should there be the GIaddr?
> If I start dhcrelay with "-a -m append" I can see the Option 82 field 
> with the value "vlan20", which is the internal interface name.
Forget it, I found the error. The customer has multiple subnets on the 
IF, the IP in the relay agent is from vlan20, but theres a vlan20:2 
interface which dhcrelay can't bind to:
Bind socket to interface: No such device

Thats why the server doesn't replay, because the scope configured 
doesn't match the relay ip :(

Any idea how to change the GIaddr on the fly or to bind to a subinterface?


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