dhcpd responding to unicast?

Martin Garbe monomartin at opennet-initiative.de
Tue Nov 10 20:35:53 UTC 2015

On 11/10/2015 11:07 AM, Simon Hobson wrote:
> Martin Garbe <monomartin at opennet-initiative.de> wrote:
>> Once the client has determined the address of a server
> How does an unconfigured client know this ?

With IPv6 devices can have many IP addresses. When clients have
predefined private IPs (ULA) they can communicate with each other. But
these IPs are not routable in the Internet. We want to use DHCPv6 to
assign dynamic public IPs.

>> , it may under
>>   some circumstances send messages directly to the server using
>>   unicast.
>> ------
>> Our scenario here is one of these "some circumstances".
> Actually, I don't think your situation is one of those circumstances envisaged.
> In the IPv4 world, once a client is configured (which requires broadcast packets), then it may unicast packets (eg to renew a lease) to the server - it knows the server address because it's part of the information supplied to it. I'm not familiar enough with IPv6 to say if this is (effectively) the same.

For IPv6 it is similar. Only broadcast is substituted by multicast.
It seems that the cited words from RFC can be interpreted in very
different ways. The usual syntax-semantic problem :)

I am/was assuming that implementing unicast-only support should be easy.
For what reason does the dhcpd not accept unicast traffic for initial
requests? In which situations is this a problem?

Kind regards,

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