DHCP Relay: Duplicate packets for DHCPRELEASE and DHCPREQUEST

Simon Hobson dhcp1 at thehobsons.co.uk
Wed Apr 18 09:08:55 UTC 2012

Sujata Verma wrote:

>I am using dhcp-4.2.2rc1. I have started the dhcp relay with options
>dhcrelay -d -i eth0 -i eth1 serverip
>everything is working fine except that when client release the ip 
>and send DHCPRELEASE packet on server side i get 3 packets for each 
>One is directly sent to server ( which is valid packet) the other 
>two are duplicate of this packet which is generated by relay agent 
>with giaddr as address of eth0 and eth1 interface.
>Is this normal behavior? The same is observed with unicast DHCPREQUEST .

Are you sure about the unicast packets ? On a switched network, the 
packet should only ever bee seen by the server - it shouldn't reach 
the relay agent.

For any boradcast packets, I'd expect to see two copies - one picked 
up directly by the server, and one picked up by the relay agent. This 
is inherent in the way the relay agent needs (due to the way it's 
built) to listen on both interfaces. I wouldn't expect to see a 
packet with the relay's eth1 address in it - they aren't connected to 
the same network are they ?

Simon Hobson

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