DHCP and 2 subnets

Chris Arnold carnold at electrichendrix.com
Mon Apr 7 11:22:13 UTC 2008

On Monday 07 April 2008 03:37:46 am Simon Hobson wrote:

> Your networks are not separate - the above request from the same
> client was received twice, once via the relay agent, and again direct
> via the attached network. Go and check your setup because this
> shouldn't be the case - you don't have both subnets connected to one
> switch do you ?

Kind of...1 router/firewall that has a "secondary ip" on the trust port. Then 
this device connects to a switch that is 192.168.123 network and off of this 
switch is another switch that is the 192.168.124 network. Do i need to use 
shared-network or some other option with this setup?
> And this is your second problem, your server is not authoritative
> (add a simple "authoritative;" statement to the top of your config) -
> so it will not send a DHCP Nack message to a client that is asking
> for an address that isn't valid (such as when it moves from one
> subnet to another).

OK, i can do this.

> >Apr  6 22:12:51 mail dhcpd: ICMP Echo reply while lease
> > valid. Apr  6 22:12:51 mail dhcpd: Abandoning IP address
> > pinged before offer
> >Apr  6 22:12:52 mail dhcpd: DHCPOFFER on to
> > 00:0b:db:c8:f1:71 (Izabella) via
> Right, and it DID make an offer for the right subnet.

Yes, i saw that too but it seems the offer was "beat" to the punch
> Leases are cached by the client, so provided it has persistent
> storage, it can continue using a lease even across restarts until it
> times out or a DHCP server says "Stop" (by sending a DHCP Nack in
> response to a request).

What i have been doing is dhcp -k and then ifup eth0. Is this clearing the 
cache or do i need to do it some other way?

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