Re: Questions about server's use of giaddr

["Michael J. Lewis" <[e-mail]>]

Awhile back, there was some activity regarding DHCP servers handling 
multiple subnets on the same physical wire.  The included note suggested 
that there may be an update to the DHCP specifications to cover this 
case although the consensus seemed to be that individual servers should 
handle this case.  Was there ever a resolution to this issue regarding 
whether the specifications will be updated or whether we need to contact 
vendors to get them to handle these cases?  As we roll out DHCP in 
Chevron, we are finding more and more situations where we have multiple 
subnets per physical wire and we've been having difficulties getting 
DHCP services to perform properly.

Thanks.

Ralph Droms wrote:
> 
> At 11:05 AM 1/29/96, Jim Fletcher wrote:
> >There are some statements that lead me
> >to assume that a server uses giaddr to decide which subnet
> >to assign addresses from for clients.  If this is true, then how
> >are clients handled which live on a LAN which has multiple subnets
> >assigned to it?
> 
> Good question.  Your're not the only one with this question - we discussed
> just this issue at the last IETF meeting.
> 
> It seems that, because the initial DHCPDISCOVER message is broadcast, some
> piece of code somewhere is going to have to a) be aware of the network
> architecture that has multiple subnets on a physical segment and b) allow
> the local netadmin to describe how to handle DHCP clients from that
> segment.  Keeping in mind the goal of "mechanism not policy", we need to
> give netadmins the ability to choose the strategy for allocating addresses
> among logical subnets on a wire.
> 
> I think the prevailing opinion is that this function will need to be
> provided by DHCP servers.  The relay agents could also make a choice of
> which address to insert into 'giaddr'; to date, we've tried to make the
> requirements on relay agents as simple as possible and so relay agents
> don't look like good candidates.
> 
> The idea, then, would be to include with DHCP servers some knowledge of how
> to select a client address based on 'giaddr'.  I.e., given a specific
> 'giaddr', the server has a pool of available subnets to choose from (all of
> the logical subnets that share the wire with the address in 'giaddr') and a
> policy for how to choose from that pool.
> 
> If the WG is in agreement about this solution, perhaps it should be written
> down in the DHCP spec somewhere.  I've posted this note back to the DHCP
> mailing lists in case there is any further comment on the issue...
> 
> - Ralph