[PATCH] Implemented support for stateless DHCPv6. Udhcpc6 will send Information-Request to request configuration parameters without IP address if using 'l' option.

[Nicolas Cavallari]

On 22/08/2019 15:53, Denys Vlasenko wrote:
> So, this looks similar to send_d6_discover() when no -d options was given,
> and "-r no" was given to suppress IP address request.
> The only difference in the packet will be D6_MSG_SOLICIT message type
> instead of D6_MSG_INFORMATION_REQUEST, right?
> 
> What happens on your network if you just use "no -d, -r no"
> with non-patched udhcpc6?

A server configured to only do stateless DHCPv6 will simply refuse your request.

>> +                               if(opt & OPT_l) /* no lease timeout will be received, use stateless timeout */
>> +                                       timeout = stateless_timeout;
> 
> So, you will be re-requesting D6_MSG_INFORMATION_REQUEST every ~12 hours,
> unconditionally (not configurable). I don't see why we can assume user
> wants this behavior.
> Users may want to have a different repetition rate. They may even want
> to do it just once.

Normally, RFC 8415 21.23 indicates that the client should request a
INFORMATION_REFRESH_TIME option and the server should indicate the maximum
refresh period. Which may be infinity for no refresh.

> 
> Overall, I think this needs a bit more thought. We seem to have
> several possibilities
> here with use cases:
> (1) user may need to request D6_MSG_INFORMATION_REQUEST after the
> usual negotiation.

This does not make sense. Per RFC 8415 5.1 this should be only used when you do
not use the DHCP server to get an IP address.

> (2) user may have e.g. static IPv6, and thus want to request
> D6_MSG_INFORMATION_REQUEST
>     *instead of* the usual negotiation...

This should also happen on a network that uses SLAAC, if the router
advertisement contains the 'O' flag ('Other configuration', RFC 4861 4.2).
In that case the client uses SLAAC to get an address and DHCPv6 inform to
get all the other information.

In fact, this is probably the most common usage of DHCPv6 information-request.