Re: [BEHAVE] (no subject)

[Mark Andrews <[e-mail]>]

In message <[e-mail]>, Simon Perreault writes:
> Le 2013-06-27 15:44, ivan c a crit :
> >> I still haven't seen any explanation why the following excerpts do not
> >> apply.
> >>
> >> RFC 4787:
> >>
> >>      REQ-3:  A NAT MUST NOT have a "Port assignment" behavior of "Port
> >>         overloading".
> >>
> >> RFC 5382:
> >>
> >>      REQ-7:  A NAT MUST NOT have a "Port assignment" behavior of "Port
> >>         overloading" for TCP.
> >
> > Because some NATs would like to do port overloading, which is in
> > contradiction with these requirements.
> 
> "Would like to" is not a valid reason. We need technical arguments.
> 
> > See section 4. of
> > http://tools.ietf.org/html/draft-ietf-behave-requirements-update-00 .
> > You're mentioned as an author on this draft by the way.
> 
> I'm not disagreeing with myself. I am only observing that this 
> discussion still has not yielded any good technical argument that we 
> could add to our draft.
> 
> I have suggested that one condition where port overloading could be used 
> is when the NAT knows that it will not disrupt the application protocol. 
> For example, the protocols running on TCP port 80 and UDP port 53 (HTTP 
> and DNS) are purely client-server and therefore would not be affected by 
> port overloading. Allowing NATs to do port overloading for those ports 
> only would probably solve the scalability problem since they account for 
> a large portion of the traffic.

And overloading DNS could potentially defeat the port randomisation
done by the server even though nameservers do port overloading
themselves to send traffic out a large set of ports choosen at
random and reselected from at random.

> Do we really need anything more complex?
>
> > In this post I explain why port overloading can be somewhat desirable:
> > http://www.ietf.org/mail-archive/web/behave/current/msg10896.html
> > I make the same point across a large number of my posts.
> 
> We know that port overloading is desirable for a number of reasons.
> 
> What we need to argue is why the undesirable effects of port overloading 
> do not apply or can be ignored.
> 
> Simon
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Mark Andrews, ISC
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