Subject: RE: [mobile-ip] 0.0.0.0 src address

From: "Lalwaney Poornima (NMP/SanDiego)" <[email-masked]>
Date: Tue, 4 Dec 2001 13:24:24 -0800

Hi,

As already discussed in this thread, the real problem is not with src=
0.0.0.0  but that if you follow RFC2002 by the word, there are cases
where the destination IP agent advertisements and registration replies
is copied from the src IP getting us to the scenario where destination
IP=0.0.0.0. We have run into this issue with some implementations and
have had interoperability concerns on this issue. I diasgree that we
have to change RFC1112 interpretation by allowing 0.0.0.0 as destination
IP; or implement an involved DHCP kind of state machine for dynamic
address assignment. 

This destination IP address (0.0.0.0) is forbidden for anything except
source (see RFC 1700 introduction). RFC1700 has a caveat that appears as
"see note later" . I have not been able to find the note either in
RFC1700 or on the updated IANA web pages. 

I do not believe that Mobile IPv4 (RFC2002 or 2002bis) intended to
create a special case by allowing "0.0.0.0" as a valid destination
address. It seems that  that 0.0.0.0 was an afterthought and all the
RFC2000 bis sections were not updated to reflect the effect of this
case. 

Could we not specify the destination IP of broadcast (255.255.255.255)
on replies for the cases where an agent receives a request with src
IP=0.0.0.0?  This is similar to what DHCP does. Uninitialized host stack
implementations accept broadcast while dropping datagrams with
destinaton IP of 0.0.0.0.  However, I think it would be an overkill to
design Mobile IPv4 clients with the DHCP behavior where the DHCPOFFER
and DHCPACK have as destination IP, the address that is to be bound to
the stack. Rather than allowing destination IP=0.0.0.0 as suggested in
this thread, why can we not use destination IP=255.255.255.255?

Now getting to link layer address on the packets with broadcast
destination IP. Can we have unicast link layer address with broadcast
destination IP as would  be required for registartion replies?

So, the following cases have to be addressed in 2002bis with regards to
dynamic home address assignment:

1) If host stack has no IP address (sends requests with src IP =
0.0.0.0), what is the destination IP on registration replies? Are both
destination link layer unicast and link layer broadcast permitted on the
reply.

2) If the host has another address bound to the interface (either
temporary or non-temporary), could that address be used for source IP
with home-address=0.0.0.0? 

Thanks..
Poornima Lalwaney

-----Original Message-----
From: ext Marc Hasson [mailto:[email-masked]]
Sent: Tuesday, December 04, 2001 10:34 AM
To: [email-masked]
Subject: Re: [mobile-ip] 0.0.0.0 src address

Samita,

(Sorry for the late response, @Home ate my own addressibility
yesterday. :-)   We'll see how my replacement cable company does
today...)

 > > It seems to me that a Mobile Node could accept its newly-assigned
 > > non-zero unicast destination address just as well as the 0.0.0.0,
it
 > > should be well-aware its in an address discovery mode analagous to
 > > DHCPv4 and process the UDP registration reply.
 > > 
 > 
 > Is there any mobile node implementation which accepts UDP
registration
 > reply destined to a newly assigned address and it's own link-layer
 > address while it sends the request with src-addr=0.0.0.0 ? 

Unknown.  This was just a suggestion on how to avoid the apparent 1122
commentary regarding destinations of 0.0.0.0 meaning the local machine
as
opposed to something on the wire.

It seems to me that DHCP implementations (perhaps with kernel stack
assist)
already handle this but I agree that mobile node implementations would
not
unless we specified it.

 > As it was pointed out that it is possible for an implementation
 > to implement this behavior in MN.  

Agreed.  I have no problem with the functionality proposed for the
0.0.0.0
address, my only commentary has been that 2002bis seems to be the first
place where 0.0.0.0 appears as a destination unicast address in a
packet.

 > I think the mobile-ip base draft rfc2002-bis needs to clarify the
 > restriction on having src-addr = 0.0.0.0 and the consequent dst-addr
 > for the registration reply from FA to MN.

100% agreed.

 > 
 > Note that it is also possible that FA may find that the registration 
 > request from  src-addr=0.0.0.0 and home-addr=0.0.0.0 is
poorly-formatted
 > or some other problem, how does it reply back with error then ? ( Due
to
 > the restriction in RFC1122 )
 > Should it drop the packet or send it to multicast addr ?

OK, good point there and perhaps I wasn't fully awake to think about
the error cases.  DHCP presumably responds with a broadcast "nak" and
lets the proper client figure it out based on the ids in the message.
The same could be done with the MN but this doesn't seem as "clean" to
me.  If it was important to avoid the apparent 1122 restriction then
thats what I would recommend but I think I'd agree that for
implementation simplicity the 0.0.0.0 handling is cleaner.

How are apparent conflicts with 1122 handled?  Just highlighted in
2002bis
since these are *mobile* host requirements, not plain hosts?

 > 
 > I wonder, why rfc2002-bis has a MUST in 3.6.1.1, could it be MAY ?
 > 
 > For example, what if any MN configures itself with a temporary
address
 > to send the reg-req with home-addr=0, to get it's newly-assigned
homeaddr? 
 > 
 > >    -  If the mobile node does not have a home address, the IP
source
 >        address MUST be 0.0.0.0.

Yep, I found this confusing too.  I *think* the first MUST "overrides"
this second one when you have a co-located COA but I agree this should
be clarified.

 > 
 > Also the draft needs to clarify that if the source-addr of the UDP
registration
 > request is 0.0.0.0, then what will be the IP dst addr for the
regReply.

Yep.

   -- Marc --

---

From: Behcet Sarikaya <[email-masked]>
Date: Wed, 05 Dec 2001 13:16:31 -0600

Hello Lalwaley,

"Lalwaney Poornima (NMP/SanDiego)" wrote:

> have had interoperability concerns on this issue.

What kind of implementations of MIPv4 you are talking about? Hope you can
share with us this info.

> I diasgree that we

--
Behcet

---

From: "Alper E. YEGIN" <[email-masked]>
Date: Wed, 5 Dec 2001 22:06:14 -0800

Lalwaney,

> destination link layer unicast and link layer broadcast permitted on the

If we don't want to coflict with rfc1122, yes, we can do this. 
255.255.255.255 should be fine. 

> with home-address=0.0.0.0? 

If the mobile node is using colocated care-of address, yes, I think
it can send a registration request using that address as the source.

> Poornima Lalwaney

alper