dhcrelay over wireless mesh

Simon Hobson dhcp1 at thehobsons.co.uk
Wed Jul 11 15:13:23 UTC 2012

Luca Tavanti wrote:

>Now, my setup is as follwos:
>((( 0 ))) ((( 1 ))) ((( 2 ))) ((( 3 )))
>I put the dhcp server on node 0, and both a dhclient and a dhcrelay 
>on nodes 1,2,and 3.
>In this way both nodes 1 and 2 gets an IP from the server (directly 
>for node 1, through the relay on node 1 for node 2).
>Yet, node 3 never gets an IP.

Use <your preferred packet sniffer> at the various network points to 
see what's being transmitted. In particular, see if a packet from 
node 3 is reaching node 0 at all, and if so, what it's GI Addr field 
contains. Also, look at how nodes 1 and 2 are getting their addresses.

My guesses at what's going wrong ...

The relay agent on node 1 is changing the GI Addr value in the 
packet, hence the reply doesn't go back to node 2 and so doesn't get 
broadcast back to the client.

The server is getting confused by the GI Addr being on a locally 
connected network, is broadcasting the reply, and the relay agent on 
node 1 is relaying it to node 2 (for node 2 getting it's address).

Simon Hobson

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