DHCP Relay: Duplicate packets for DHCPRELEASE and DHCPREQUEST
dhcp1 at thehobsons.co.uk
Wed Apr 18 11:51:06 UTC 2012
Sujata Verma wrote:
>My setup is like this :
> Windows 2003 server (
>192.168.9.2/23)-------------------(192.168.8.177/23) Linux PC(Relay)
>(188.8.131.52/24----------eth0----Windows XP Client ( DHCP client
>getting IP 184.108.40.206/24)
>I am attaching the wireshark capture for both client and server. In
>this we can see that the DHCPDISCOVER is only being sent once to the
>server which relay is forwarding while adding giaddr field as
>When DHCPRELEASE packet is being sent, it is sent directly to the
>server and with other two packets as duplicates with giaddr as of
My guess (I've not actually used the ISC relay) is that it's sniffing
the packets and picking up the unicast packet from the client to the
server both when it enters the relay on eth0 and when it exits via
eth1. That, to my understanding, is wrong.
It would be interesting to see what happens to a unicast DHCP-Request
packet ? The Request packet in your captures is a broadcast packet
which is being relayed by the Relay Agent (correctly). You will need
to (temporarily) tweak your server config down to a short lease time
so that the client will renew in a timescale that's workable.
Based on the above, I suspect you'll see those packets duplicated as well.
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