DHCP RENEW on Multi homed client

Chris Buxton cbuxton at menandmice.com
Wed Nov 25 08:13:13 UTC 2009

On Nov 24, 2009, at 2:15 PM, Jolynn Schmidt wrote:

> Hello,
> I am trying to understand a problem we are seeing and understand what options are available to me.
> We have servers that are dual homed
> eth0 - 10.114.10
>         default gateway on host is out eth0 to
> eth1 - 10.114.12
> DHCP Server on 10.114.100
> We have DHCP helpers in place for both 10.114.10 and 10.114.12 to point to our DHCP server on 10.114.100.
> Eth0 and Eth1 have no problem getting their initial dhcp request, but we are having problems when dhclient for eth1 renews it's lease.   The default gateway points out eth0 so the renew for eth1 is being sent out eth0, I see the request and ack transaction occur between the server and the client on eth0 but dhclient for eth1 never sees it, and just keeps send out a request over and over again. 
> Is this just not going to work, do I need to static address my eth1 interface or should this be working?

Correct, this is not going to work. DHCP depends on determinate routing, and you're breaking that with this scenario.

Either statically configure eth1, or else set up different DHCP server addresses for the two sides, on different subnets, and reconfigure the affected relay appropriately.

Chris Buxton
Professional Services
Men & Mice

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