Okay... I'll bite...
Maybe I am just naive but if the IP header did not contain a source
address, how would TCP acknowledgement, windowing, or re-transmission take
How would a request for data be serviced? Would responses always be in
the form of a all-nets/all-hosts broadcast? How else would the response
get back to the originating host?
The point is that the source address is not explicitly *required* in the
*header*. Thus, a source and destination could "setup" an IP session by
negotiating a "session ID" or something - the first packet from source to
destination would include the source's address in the *payload* along with
information to start the negotiation process. I am describing, in other words,
something like an ATM transport layer that would live below IP.
Routing Protocols.... we need source addressing so we know, at the IP
layer, who our sources of information are, and then, who can we accept
information from and who we should refuse information from. In addition,
access-lists, route-filters, and other types of security would be
non-functional without source addresses.
Now you're addressing (so to speak the kind of issues that I am concerned
with: without mandating source information in the header, how can the
destination make decisions about rejecting/accepting traffic? alternatively,
how can middle agents (e.g., routers) do filtering, etc.? how can we
possibly prevent spoofing?
Lastly, how would you accomplish a traceroute on a network with no source
addressing? Where would the ICMP ttl expired messages be directed if
there was no source address in the packet?
I don't know! You tell me! Do we make each intermediate router "aware" of
the negotiated session ID? Doesn't sound tractable to me.
I hope this clarifies this - I don't think it is so strivial as my initial
email led you to believe.