[Dibbler] Relay Configuration Problem

Tomasz Mrugalski thomson at klub.com.pl
Wed May 11 01:07:11 CEST 2005

On Wed, 4 May 2005 somebody known as Jimmy Ott wrote:

> .. but, i have still a problem with the relay, and now, it doesn't look
> so easy as yesterday.
> same network layout, same config, but new relay from cvs.
> relay log:

> 2005.05.04 09:33:46 Rel Critical  | Dibbler - a portable DHCPv6, version 0.4.0-CVS (May  4 2005 00:24:08) (RELAY)
> 33:51 Notice    Accepting messages.
> 34:03 Debug     Received 80 bytes on the Local Area Connection/5
> interface (socket=1728, addr=fe80::200:39ff:fe10:3aa2, port=547).
> 34:04 Notice    Received SOLICIT on Local Area
> Connection/5,TransID=0x28de, 4 opts: 1 3 8 6
> 34:04 Notice    Relaying message on the Local Area Connection/5
> interface to unicast (fd00:0:0:3::a) address.
> 34:04 Notice    Accepting messages.
> 34:04 Error     sock_recv(1752,...) failed.

1. Ok, I have investigated that problem and I belive I have found cause of 
this. Let me explain:

I get this error when relay tries to forward packet to server, but server 
does not have port open. In such circumstances, server's operating system
sends IMCPv6 Port Unreachable packet, which is being received by the 

I have changed this message to someting more meaningful. It currently says 
"Send failure detected (probably ICMPv6 Port Unreachable message 
received). Are you trying to forward message to an invalid or unbound 
unicast address?". I'll check it in/prepare Windows binary of the CVS 
snapshot soon, propably tomorrow.

You can investigate this issue with ethereal, tcpdump or any other packet 

2. To reproduce this issue, I have used 2 hosts: dexter (relay) and falcon 
(server/client) connected with only one interface. It seems that this 
message appeared only when I had properly configured addresses and 
routing, but had server disabled. As for relay using one interface - it 
works ok, so you can safely ignore following warnings: "There is only one 
interface defined. At least two is a sanite configuration." and "Both 
server and client support is defined on the eth1/5 interface.". Oh well, 
I'm telling users to ignore my own warnings...

3. As I said before, that one-interface relay is weird and not 
recommended. You have said that you are using Cisco routers. Cisco IOS 
supports DHCPv6 relaying. As for Dibbler, it support Cisco relays since... 
well, yesterday :) Andre Stolze from JOIN project has provided me with his 
cisco configuation. Here it is:

1. Relay-Config. I use cisco's relay on a 7206 with IOS  12.3(14)T

Here's the config:
interface GigabitEthernet0/0.200
description RZMITARB
encapsulation dot1Q 200
no ip proxy-arp
no ip route-cache
no ip mroute-cache
no snmp trap link-status
ipv6 address 2001:638:500:200::/64 eui-64
ipv6 enable
ipv6 dhcp relay destination FF05::1:3


Hope that helps.

Ok, it's after 1am. Time to sleep.


Tomasz Mrugalski,              | "I think there is a world market for     |
thomson(at)klub(dot)com(dot)pl |  about five computers."                  |
                                |     Thomas J. Watson (Chairman, IBM) 1943|

More information about the Dibbler mailing list