Relay and Option 82 reports wrong GIADDR address - ISC version 3.0.5-7

Simon Hobson dhcp1 at thehobsons.co.uk
Wed Oct 8 09:50:19 UTC 2008


Martin Hansen wrote:

>I have a dhcp relay on selected VLANs that adds opt 82 string - Then 
>when the value arrives to ISC DHCPd, it has the wrong GIADDR causing 
>the DHCPd to give an error
>The GIADDR is ofcourse the MGMT IP of the Switch there have Relaying enable..

Then the switch is configured wrong. The GI Addr MUST be in the same 
IP subnet as the client, OR in any IP subnet that is part of a shared 
network (which is NOT the same as a VLAN) with the client.

If your switch is using a GI Addr that is NOT in the clients IP 
subnet then your switch config is wrong.



However, it looks like you are trying to do things the hard way !

>shared-network lab-besteffort-vlan-10 {
>         subnet 172.16.10.0 netmask 255.255.255.128 {
>                 pool {
>                         allow members of "lab-besteffort";
>                         max-lease-time          120;
>                         default-lease-time      120;
>                         range 172.16.10.32 172.16.10.63;
>                         option routers 172.16.10.1;
>                         option broadcast-address 172.16.10.127;
>                         option subnet-mask 255.255.255.128;
>
>                         log(info,concat("lab-best-effort-vlan-10: 
>",binary-to-ascii(10,8,".",option agent.circuit-id)));
>                 }
>         }
>} # shared-network lab-besteffort-vlan-10

The shared network here is redundant - there's only one subnet so no 
shared network.


You then proceed to match clients to subnet using option 82. This can 
be done automagically by simply configuring the switch to use the 
right GIAddr for each VLAN - then the server will match clients with 
the right IP subnet automatically.


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