[Dnsmasq-discuss] dhcp doesn't work with dnsmasq in multi ip environment

Simon Kelley simon at thekelleys.org.uk
Sat Aug 13 20:37:13 BST 2016


On 09/08/16 08:23, Kolmann Philipp wrote:
> I have checked the isc-dhcpd man page and found there a switch for dhcp-server-identifier. I have tested my power-socket with isc-dhcpd with the following setup:
> 
> shared-network eth1 {
>   subnet 172.18.92.0 netmask 255.255.255.0 {
>   }
> 
>   subnet 172.17.32.0 netmask 255.255.255.0 {
>   }
> }
> 
> host fh-tuck-1p {
>   hardware ethernet 00:19:32:00:8f:90;
>   fixed-address 172.17.32.8;
>   option host-name "fh-tuck-1p";
>   option dhcp-server-identifier 172.17.32.1;
> }
> 
> Now I see in the DHCP-ACK Message the source-ip of the packet and the server identifier both set to 172.17.32.1.
> 
> I suspect, that the power-socket dhcp client has a problem, if the packet source ip and the server-identifier are not set the same.
> 
> Would it be possible to set the packet-source ip and server-identifier to the same ip address?
> 
> Thanks
> Philipp
> 

That's not something that can be done in general: there are
circumstances where the server-id is not an address which belongs to the
host sending the DHCP packet. For instance is the DHCP reply is returned
by a DHCP relay, then the server-id will be the address of the server,
but the packet will be sourced by the relay agent, which won;t have an
interface with that address. If your DHCP client is really rejecting
packets where source address != server_id, then it's broken.

I thought about modifications to set the source address when possible,
but I fear that it will just provoke a different set of bugs in
different clients.


Cheers,

Simon.


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: OpenPGP digital signature
URL: <http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/attachments/20160813/c028fb5c/attachment.sig>


More information about the Dnsmasq-discuss mailing list