A lot DHCP REQUEST

Peter Rathlev peter at rathlev.dk
Tue May 8 21:49:39 UTC 2012


On Tue, 2012-05-08 at 15:11 -0430, Nelson Perez wrote:
> I use DHCP ISC on my network architecture, but I have noticed that
> some clients are sending a lot of DHCP REQUEST, even if the client
> does ACK for the REQUEST, the log is: 
>  
> May  7 05:15:53 dhcp-isc-01 dhcpd: DHCPREQUEST for 190.72.35.198 from 00:30:67:47:a9:f6 (oriana) via 172.17.49.239
> May  7 05:15:53 dhcp-isc-01 dhcpd: DHCPACK on 190.72.35.198 to 00:30:67:47:a9:f6 (oriana) via 172.17.49.239
> May  7 05:15:58 dhcp-isc-01 dhcpd: DHCPREQUEST for 190.72.35.198 from 00:30:67:47:a9:f6 (oriana) via 172.17.49.239
> May  7 05:15:58 dhcp-isc-01 dhcpd: DHCPACK on 190.72.35.198 to 00:30:67:47:a9:f6 (oriana) via 172.17.49.239
...
> Is there any way to avoid this behavior?

Disconnect the client from the network. ;-)

The ACK is what the server sends as a reaction to the REQUEST, not
something the server sees from the client.

You might be dealing with a retarded client. Do you happen to know what
operating system and DHCP client software you're dealing with?

You might also have some kind of network related problem from the server
to the client, meaning that the ACK never reaches the client. This might
theoretically be a firewall on the client itself.

Since the client keeps retrying at 5 second intervals my guess is that
it's not an ISC dhclient, since that one uses exponential backoff.

If you just want to block this specific client and not log anything then
take a look at this:

https://lists.isc.org/pipermail/dhcp-users/2011-February/013001.html

-- 
Peter




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