Excessive DHCP requests in /var/log/messages: DHCPINFORM, DHCPACK and DHCPREQUEST repeated

Looks like you have clients connected to multiple subnets (or routers that are relaying dhcp helper to each other). Since I am not privy to your topology, I can't say for sure.

A few things to check:

1. Does this happen to all clients? Or just those located on a specific network segment?
2. Are those clients connected to multiple subnets?
3. Have you verified that there's no bridging between your subnets?

And you should look at each of your clients, perhaps with ethreal, and determine if they are receiving multiple DHCPACK from multiple routers (they probably are).

Some clients (notably Windows 7) constantly sends DHCPINFORM messages if there is no WPAD option specified in the DHCPACK response.

You can fix this for ISC DHCP by adding the following lines to your config:

option wpad code 252 = text;

subnet xxx {
    option wpad "\n";
}

You can fix this for dnsmasq by adding the following to the dnsmasq.conf file:

dhcp-option=252,"\n"