[Dibbler] relay server configuration - icmpv6 port unreachable

Tomasz Mrugalski thomson at klub.com.pl
Wed Feb 13 19:05:44 CET 2013

On 13.02.2013 11:07, Salim Engin wrote:
> Hi all,
> I have been trying a setup where  dibbler dhcpv6 server has to assign
> ipv6 via relay .
> dhcpv6 relay is a router between client and dhcpv6 server .
> Without relay, if the client is connected to server directly, it can get
> ipv6 address. But if it is connected through relay, even though dhcpv6
> server receives dhcpv6 relay forw  message, it does not send relay
> reply. Instead, I see "icmpv6 port unreachable"  being sent to router .
> It does not matter if dhcpv6 server is running or not. This message is
> always sent .
> icmpv6 port unreachable message is sent if the port is not available.
> However, as the server provides IP to the directly connected users and
> as we see udp port 547 is open, why the linux sends that message ?
> debian:/etc/dibbler# lsof -i :547
> dibbler-s 706 root    5u  IPv6 12955868      0t0  UDP
> [ff05::1:3]:dhcpv6-server
> dibbler-s 706 root    6u  IPv6 12955871      0t0  UDP
> [ff02::1:2]:dhcpv6-server
What does the relay forward messages to? What's the destination address?

If the relay agent has not been explicitly configured, it MUST use the
All_DHCP_Servers multicast address as the default. See section 20 of
RFC3315. It seems that dibbler properly listens on that port. Perhaps
your relay sends the packets to specific unicast address? That is
allowed behavior, but Dibbler server must be explicitly configured to
listen on that address. See examples of "unicast" in server.conf. They
are explained in Dibbler User's Guide somewhere.

Hope that helps,

More information about the Dibbler mailing list