Date:	Mon, 25 May 2015 16:17:43 -0700
From:	Coroutines <coroutines@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Question: Now that we have IPv6, do we need TCP/UDP port numbers?

I have a potentially dumb question to ask, and I'm posting it here
because out of everywhere on the web I thought I would find the most
experts relating to TCP/UDP's design/handling and its history here.

I've recently started educating myself about Tor, about how you can
bind a service to a local address+port and then host a hidden service
that others can connect to from an onion address like this:

32rfckwuorlf4dlv.onion

Just to be clear: This address provides a single service, you do not
specify a port to "request" a specific service.

I was thinking was that when TCP/UDP were designed, internet port
numbers were thought up because it wasn't practical/easy to just
register/allocate and assign another IPv4 address.  Today those of us
with awesome ISPs are advertised /64's for a network prefix and we can
do whatever we want claiming an address within /64 the gateway router
will pass traffic to/from.  (IPv6 Stateless Address Autoconfiguration
without privacy extensions enabled is evil btw)

My point is this - we have a LOT of room to create addresses as needed
- single-service addresses.  I was wondering if there are any
absolutely necessary reasons we need ports - or if there would be
benefits/advantages to getting rid of them.  Would TCP/UDP be easier
to process in-kernel if it were only addresses?  Would it eliminate
any ambiguities between Linux/Windows/FreeBSD networking stacks?
Would reclaiming 4 bytes from the TCP/UDP structs be worth it (32 bits
isn't usually word-size anymore).  It would definitely make port scans
impractical if you tried to scan the assumed /64 host range of an
address.  It would also mean no more expecting to find a service at a
specific port (which I consider bad because it makes hosts easier to
identify in a scan).

We're used to being able to go to port 80 (HTTP) and port 22 (SSH) at
a single address and "knowing" that we're accessing the same machine.
For typical setups this is true, but for servers running reverse
proxies to pass traffic through to another host this is not so true.
((Imo)) it would be no different having a single, separate address for
each service.

Furthermore, most of domains we go to are single-service - like
navigating to gmail.com in a web browser.

I thought it would be cool to have one address responding to name
queries so DNS servers become more like a port mapper in the current
sense. Asking for smtp.domain.tld would tell you the only address that
would accept SMTP/mail traffic. (example)

Anyway, again I want to say I'm sorry if this is the wrong place to
dream about the future (or talk about the past).  I am new to the list
and I couldn't think of anywhere else I might find experts in this
area so closely related to its history.  IPv6 adoption has been slow
so even if TCP/UDP/SCTP were redesigned to eliminate port numbers I
doubt the revised protocols would be adopted quicker.  I just want to
know the history and the reason for internet ports, if not simply to
multiplex traffic to a limited number of addresses.  Is it just a
convenience or was it a necessity for IPv4?  I'm not going to reply to
anyone who responds (as I believe I'm off-topic), but I will read
everything offered to me to learn from.  I want to know what you all
think, by asking what I consider to be an original question.

(thanks for reading)
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