Re: TCPMUX (RFC 1078) status

[Joe Touch <[e-mail]>]

On 8/15/2013 10:38 PM, Martin Sustrik wrote:
> On 16/08/13 03:23, Wesley Eddy wrote:
>
>>> There are semantics issues to; see draft-touch-tcp-portnames-00 for
>>> information (this is being revised for resubmission shortly, FWIW).
>>>
>> I totally agree.  In fact, in the update to the TCP roadmap [1], we
>> added TCPMUX to the section on "Historic and Undeployed Extensions",
>> though it definitely bears further discussion than is currently in
>> the roadmap.  I think we should add a reference to your portnames doc
>> to explain why this should be Historic plus check a bit more to see if
>> the code that's out there is really being used or whether it's just
>> hanging out like a vestigal limb in the various inetd packages.
>>
>> If it's fair to ask Martin ... I'm kind of curious why you might want
>> to be using it or think it sounds useful?  I think a lot of admins
>> would be concerned that it could be used to get around port-based
>> firewall rules, etc.
>
> Ok, let me explain.
>
> I am coming from enterprise messaging world (think of IBM MQ series,
> JMS, ActiveMQ, RabbitMQ et c.)
>
> Once I was participating on AMQP protocol development (now at OASIS).
> So, what AMQP and other enterprise messaging products do is exposing a
> "message broker" on a single TCP port, which then forwards messages to
> any connected services. As can be seen, single open firewall port can be
> used to access any internal service.

I don't understand that statement.

Services are currently indicated by the destination port. If there is 
only one destination port available, there is only one service provided 
- because very few services can be identified solely by in-band information.

> That being obviously the *wrong* way to do things, I've written ZeroMQ
> later which takes the strict approach: If you want to expose a new
> service, you have to use a separate TCP port number.
>
> Since then it turned out that this as a limitation that people are most
> complaining about.

It would be useful if you could be more specific about the problem you 
are trying to solve.

So far I hear "people want one port that serves multiple services". I'd 
like a pony ;-) I.e., just because they want it, doesn't mean it either 
makes sense or should get it.

> Now, the reason seems to be that ZeroMQ requires you to use different
> TCP connections for doing different kinds of stuff to avoid head-of-line
> blocking et c. (think of SCTP channels simulated via TCP)

Different connections don't have anything to do with the use of a single 
port. A single port can serve multiple connections, and yes - that's a 
useful way to avoid HOL blocking.

> What that means is that you have a lot of fine-grained services and as
> the development of your application proceeds you add more of them,
> remove them and so on.
>
> That in turn requires admins (and the corporate approval process!) to
> get into the deployment cycle and open the TCP ports as appropriate. The
> result is that the development basically grinds to halt.

That sounds a lot like the desires of admins is in conflict with the 
desires of your users. I.e., an admin that wants to block anything they 
don't explicitly allow WANTS to block this sort of mechanism too.

> The solution IMO is to preserve the port-based services functionality
> for those that truly care about security and -- optionally -- support
> some kind of multiplexer such as TCPMUX for those that care more about
> short deployment cycle.

TCPMUX won't do what you're asking - if you're asking to block based on 
the service type. If it did, then the sysadmin would just block TCPMUX 
connections to services they didn't know, and you'd be right back where 
you are now (i.e., without TCPMUX).

Again, what is the goal?

(note: the goal of the portnames approach is NOT to provide a single 
multiplexing port; it's to decouple the dest port's two uses - demux 
info and service identifier. the primary reason for portnames is to 
allow more than 65K concurrent/timewait connections to a single service; 
FWIW, I cited it because of its description of the limitations of 
TCPMUX, not because the approach there was relevant here).

> That being said, IIRC, there's such functionality in WebSockets as well.
> Open a connection to fixed pot (80) and particular URL (string), then
> after the initial negotiation, switch to raw TCP mode and hand the
> connection to whatever application is suppose to handle it. The reason I
> don't like that solution is that you have to have web server installed
> to work as a multiplexer, which is kind of strange.

If you want a multiplexer to serve different connections from a single 
service port, you need a multiplexer server (tcpmux daemon, websockets, 
whatever you want to call it).

Joe