Subject: [mobile-ip] 0.0.0.0 src address

From: Sivasundar Ramamurthy <[email-masked]>
Date: Thu, 29 Nov 2001 17:15:41 -0800 (PST)

Hello,

This is regarding draft rfc2002 bis-8 wrt using 0.0.0.0 as the IP
source of registration requests. I have only recently joined this
email group so please bear with me if this had been discussed earlier.

Section 3.6.1.1 states that the Mobile Node must use 0.0.0.0 as the IP
source address of the registration request if it does not have a home
address. Section 3.7.2.3 states that the FA must use the
IP source of the request as IP destination address when forwarding
replies. 

Thus there might be cases where the FA must forward replies to the
address 0.0.0.0. This task appears "impossible" since rfc1122 defines
0.0.0.0 as something like "this machine on this network", like
loopback. So a packet with destination address 0.0.0.0 might never go
out of the FA.

Am I in the right here? Can someone please clarify the usage/handling
of 0.0.0.0 as the source address of registration requests?

Thanks in advance!

Siva

---

From: "Alper Yegin" <[email-masked]>
Date: Fri, 30 Nov 2001 13:36:08 -0800

Hi Siva,

The foreign agent should use the link-layer address of the incoming (from
MN) packet
to send back the responds to the MN. So, FA can send a packet with 0.0.0.0
IP destination
address and MN's link-layer address as the destination MAC address.

For that, foreign agent should note the source link-layer address of the
incoming packet.

The same can also happen with simple rotuer discovery (sending router
solicitation, and
receiving router advertisement). Please see rfc1256.

alper

---

From: Sivasundar Ramamurthy <[email-masked]>
Date: Fri, 30 Nov 2001 14:05:47 -0800 (PST)

Hi Alper,

thanks for responding to my email.

> receiving router advertisement). Please see rfc1256.

I agree with you regarding the usage of the link-layer address, which
is standard means to forward replies to the MN. However, from the
dicussions I have had with my "Transport" collegues regarding the
usage of 0.0.0.0 as a dest address of a IP packet, it seems that:

  The destination of 0.0.0.0 means "this machine on this network". So
  by definition we CANNOT send a destination address of 0.0.0.0 onto
  the network. This address is also used as a special address for DHCP
  as a _source_ address. However it is not used as a destination.

I was given RFC 1122 as a reference regarding the definition of
the destination address 0.0.0.0. 

And for the same reason, an arp entry cannot be made at the FA to bind
the MN's link-layer address to the IP address 0.0.0.0, which is
required to forward the reply.....

Am I still missing something here? :-)

thanks!

Siva