udhcpc6 missing source address

[Denys Vlasenko]

On Fri, Dec 9, 2022 at 5:09 PM John Lemonovich
<john.lemonovich at foresys.com> wrote:
> Hello Denys,
>
> I am working on an embedded Linux project using an intel Arria 10 FPGA and have been using IPv4 for a long time, and now need IPv6.  I found your email online searching for help.  I have many things working with IPv6, but the one thing I can’t get to work is udhcpc6 – it will not acquire an IP address via DHCPv6 (tried with multiple servers).  I’m really stuck and looking for any help – even a pointer to documentation maybe I’m missing?

Sorry, I myself have no DHPCv6 server to test against...

> If I look at the tcpdump output – the solicit packets go out with a null source address (all 0’s  - just as  ::  )

Which kind of makes sense, if you think about it. DHCP client does not
_have_ an IP address yet,
this is the whole point of DHCP: to obtain an address...

> and the server doesn’t know how to reply (unreachable).

I would imagine server can/should reply with a broadcast, right?

> My link local address is set to:
> inet6 fe80::da80:39ff:fed8:90a0  prefixlen 64  scopeid 0x20<link>
> but yet udhcpc6 seems to put just  ::  in for the source address.

But what if the iface has no link-local address either?
Then udhcpc6 would have no choice but leave it not filled.
And a good server implementation should deal with such incoming packets.

> If there’s a better place to post this - please let me know.

CCed to busybox ML.