Re: ARP and DHCP: one more question

Rogier Wolff (
Wed, 21 Jan 1998 10:38:42 +0100 (MET)

Sergei Viznyuk wrote:

> I think I might have seen this question here already but I missed
> the answer if any.

> According to RFC 2131 a DHCP client after receiving DHCP_ACK message
> from DHCP server but before configuring network interface must
> verify the validity of offered IP address supposely by broadcasting
> ARPOP_REQUEST message and reading ARPOP_REPLY in a case the offered
> IP address already exists.

It is the normal "gratuitous arp" (or some such). What you do is:

10:30:27.187875 <new-ozon-hw-addr -> broadcast> arp who-has ozon tell ozon
10:30:27.187875 <old-ozon-hw-addr -> new-ozon> arp reply ozon is-at x:y:z:u:v

if there is a host with IP address "ozon" it will reply to the new
ozon-hw-addr, at which point, the new ozon should reject the new IP
address it got using DHCP (or through whatever other means).


** ** +31-15-2137555 ** **
Florida -- A 39 year old construction worker woke up this morning when a
109-car freight train drove over him. According to the police the man was 
drunk. The man himself claims he slipped while walking the dog. 080897