udhcpc6 missing source address

[David Laight]

From: John Lemonovich
> Sent: 13 December 2022 20:35
> 
> How are you getting a solicit message through with  ::  as the source address, which I've found no
> server likes as I've tested 3 of them?  Or is mine not using the link local address because I'm not
> doing anything with the default.script?
> 
> The kernel is 5.4.13

I've just run a quick test.

strace of uhdcpc6 shows it doing something with a routing socket,
creating an IPv6 UDP socket, binding (probably to the interface)
and then doing s sendto() that specifies the multicast MAC.
(It puts the mcast address in the bind as well - probably ignored?)

The kernel is providing the source IPv6 address as part of its
normal UDP routing operations - the same as it does for any
other outbound packet.

tcpdump then shows the packet being sent from the link-local
address - as expected.

Three messages are sent, no reply received (I don't have a server
here and there is absolutely nothing else on that network segment).
The script is run 'leasefail' and it all retries a short time later.

On a network with a server it gets a response.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)