Philip Guenther | 6 Nov 23:15
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Re: Service vs. Port vs. SRV (following Eliot's presentation)

On Mon, 6 Nov 2006, Ned Freed wrote:
>> This is in response to Eliot's presentation this morning, in the 
>> AppsArea and it is merely intended to solicit comment:
>
>> I have always understood the construct of Well-Known Ports as being a 
>> means of standardizing an efficient rendezvous mechanism, for clients 
>> to find servers. -- without quibbling about the terminology that might 
>> better cover use in peer-to-peer scenarios.
>
> I think you're talking past each other here. You're referring to our 
> practice of saying things like "SMTP servers listen on port 25 by 
> default" or "HTTP servers normally listen on port 80". Eliot is talking 
> about ports with numeric values less than 1024 being handled distinctly 
> from those above 1024.

Elliot was talking about both in his presentation.  The first bit was this 
whole thing involving ports 0 to 1023 (which the registry calls "Well 
Known Ports").  The second bit was the recommendation that new protocols 
should consider using SRV instead of having a particular port number.

> I am complete agree with Eliot that the "below 1024 are special" 
> notion's time has long since past. It made sense back in the mainframe 
> era, but it was over the minute we started putting machines directly 
> under the control of random users.

I agree.

> I certainly don't want to abandon the practice of defining ports 
> associated with specific services and I don't think Eliot is saying that 
> either.
(Continue reading)

Stig Venaas | 7 Nov 15:41
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Re: Service vs. Port vs. SRV (following Eliot's presentation)

Philip Guenther wrote:
> On Mon, 6 Nov 2006, Ned Freed wrote:
>> I wasn't entirely clear on what Eliot was trying to say about SRV 
>> records.
>> Perhaps someone could recap that here?
> 
> 
> SRV records good:
>  - provides fallback/load-balance location mechanism
>  - avoids tight port # binding
>  - namespace of assignments is strings (that can be a DNS label) instead
>    of 16bit numbers
> 
> SRV records bad:
>  - add dependency on DNS
>  - add latency on first connect, maybe later
>  - complexity

Another issue is that there is no standardised API (AFAIK) for
retrieving SRV records. It would be good to have some standard
API to make it easier to write portable applications using SRV.

Not sure if IETF is the right place, but we have done things
like getaddrinfo()...

Stig

> 
> 
> Philip Guenther
(Continue reading)

Ned Freed | 6 Nov 23:16

Re: Service vs. Port vs. SRV (following Eliot's presentation)

> On Mon, 6 Nov 2006, Ned Freed wrote:
> >> This is in response to Eliot's presentation this morning, in the
> >> AppsArea and it is merely intended to solicit comment:
> >
> >> I have always understood the construct of Well-Known Ports as being a
> >> means of standardizing an efficient rendezvous mechanism, for clients
> >> to find servers. -- without quibbling about the terminology that might
> >> better cover use in peer-to-peer scenarios.
> >
> > I think you're talking past each other here. You're referring to our
> > practice of saying things like "SMTP servers listen on port 25 by
> > default" or "HTTP servers normally listen on port 80". Eliot is talking
> > about ports with numeric values less than 1024 being handled distinctly
> > from those above 1024.

> Elliot was talking about both in his presentation.  The first bit was this
> whole thing involving ports 0 to 1023 (which the registry calls "Well
> Known Ports").  The second bit was the recommendation that new protocols
> should consider using SRV instead of having a particular port number.

> > I am complete agree with Eliot that the "below 1024 are special"
> > notion's time has long since past. It made sense back in the mainframe
> > era, but it was over the minute we started putting machines directly
> > under the control of random users.

> I agree.

> > I certainly don't want to abandon the practice of defining ports
> > associated with specific services and I don't think Eliot is saying that
> > either.
(Continue reading)

Dave Crocker | 6 Nov 23:32

Re: Service vs. Port vs. SRV (following Eliot's presentation)


Ned Freed wrote:
> ..., but I also think there's a point past which they'd be overused.

Can you characterize that limit in some technical or administrative terms?

d/
--

-- 

   Dave Crocker
   Brandenburg InternetWorking
   bbiw.net

Ned Freed | 6 Nov 23:50

Re: Service vs. Port vs. SRV (following Eliot's presentation)


> Ned Freed wrote:
> > ..., but I also think there's a point past which they'd be overused.

> Can you characterize that limit in some technical or administrative terms?

I think Phillip's pro and con lists are a start at expressing the criteria for
making a selection between the two mechanisms. There are some clear cases at
the edges, e.g. services that run "below" DNS or which have real time response
requirement cannot use SRV, and services that need lots of redundant servers
with fallback and prioritization should use SRV instead of a bunch of A
records.

We specified use of SRV records in the MSGTRK work and it seems entirely
appropriate to use them in that case. I don't have a candidate protocol
currently being developed in mind where I'd like to see SRV records used, but
sooner or later there will be one.

				Ned


Gmane