On Tue, Oct 30, 2007 at 03:40:06PM -0700, Templin, Fred L wrote:
> At the risk of further diversion on what may/may-not be
> a problem:
> 
> > > It's just a proposal, and I haven't studied the problem
> > > (if there is one) in detail. But, I don't agree wrt the
> > > simplicity aspect.
> > 
> > - An additional mechanism would be needed for DHCP client and DHCP
> > relay/server to know the IP-in-IP capability as well as 
> > the tunnel endpoint address of the peer.
> 
> I was thinking that IP-in-IP would be used IFF messages
> that support authentication are used. So, the use of the
> authentication messages implies the use of IP-in-IP encaps.

In that case, how the DHCP client can know that authentication
messages needs to be used?

> 
> > - Use of IP-in-IP with IPv4 Link-Local address for DHCP would
> > introduce not only potential for collision in the server/relay's
> > reassembly cache,
> 
> But, much less so than for the unspecified source address.
> and any collisions would be detected by udp checksums and
> dropped. Result is that client simply retries.   

I think that a collision must not happen.  If not, it's not the right
approach, IMO.

> 
> > but a requirement for DHCP server/relay to maintain
> > mapping between hardware address and IPv4 L-L address of DHCP client,
> > because hardware address is no more sufficient to deliver DHCP message
> > to DHCP client. 
> 
> I'm not entirely sure this is true, and if it were I don't
> necessarily see a problem; the server could just echo the
> LL in 'yiaddr'.

I don't think DHCP server is supposed to include in 'yiaddr' an
address that is not allocated by the server

> 
> > These issues would affect the following requirement
> > in RFC 3927 on IPv4 L-L address: "A host MUST NOT alter its behavior
> > and use of other protocols such as DHCP because the host has assigned
> > an IPv4 Link-Local address to an interface."
> 
> There are two interfaces in question: 1) the interface
> connected to the physical link over which the client is
> attempting to configure a global address,  and 2) the
> virtual interface used for IP-in-IP encapsulation. The
> RFC3927 address would be assigned to interface #2; not
> interface #1. By my read of the RFC3927 text you quoted,
> the concern is specific to the case of both LL and global
> being assigned to the same interface; not different ones. 

I am not sure if I understand your comment.  Isn't RFC3927 address
assigned to the physical interface?

Yoshihiro Ohba



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