Subject: what is a site???

From: "Paul Francis" <[email-masked]>
Date: Fri, 23 Mar 2001 08:11:05 -0800

When I presented the near-unique stuff in IETF50 yesterday, Deering stated
from the mike that a site is a location in space (geographical region,
whatever...I don't remember Steve's exact wording).  This had me totally
baffled---and it isn't fun to be baffled in front of a couple hundred
people.

It had me baffled because it doesn't make a lot of sense (it begs certain
nonsensical questions like, how big can it be (in square meters), if you
have five routers, one each in New York, Maimi, Chicago, LA, and San
Francisco, all connected by dedicated links, with only a single ISP
connection point, is this a site, or is it too big or too sparse to be
considered a site, etc. etc.)?

Given that this statement came from somebody as authoritative as Steve, and
that nobody disagreed with it, I naturally assumed that I must have hastily
glossed over some important piece of text somewhere, and felt embarrased for
apparently not having done my homework and for having such a fundamental
mis-understanding of IPv6 (and it isn't fun to be embarrased in front of a
couple hundred people).

So I started doing some homework.  There is nothing about sites in 2460.
There is nothing that defines sites in draft-ietf-ipngwg-addr-arch-v3-03.txt
(though it talks a lot about sites).  draft-ietf-ipngwg-site-prefixes-05.txt
has a section called "What is a Site?".  This section starts by saying that
it "does not attempt to define the concept of a site", but then goes on to
say "A site is an administratively controlled piece of topology that is well
connected".  This is much closer to what I was thinking (though I probably
would have defined it as a connected piece of topology whereby SLA
assignment is coordinated or some such thing).  Erik's definition in any
event clearly has nothing to do with geography.

I could continue to wade through IPv6 specs to find the definition of site.
But at this point I don't think the onus is on me to do so.  Rather Steve I
think the burden is on you to point me to this illusive piece of text that
defines what a site is.

Thanks,

PF

--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page:                      http://playground.sun.com/ipng
FTP archive:                      ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [email-masked]
--------------------------------------------------------------------

---

From: Kevin Wang <[email-masked]>
Date: Fri, 23 Mar 2001 10:40:12 -0800

Hi, Paul,

You had a very good question - a question I wanted to ask but was afraid I would
be considered too careless in IPv6 specs. Seems 'site' in IPv6 is an elastic
concept - it all depends on how big your heart is ;-) . But in reality when I
tried to learn to configure the 6Bone connection, I was baffled too.
Hope you can give us a concise and practical definition very soon.

Best regards.

Kevin

---

From: Steve Deering <[email-masked]>
Date: Fri, 23 Mar 2001 20:08:43 -0800

>baffled---and it isn't fun to be baffled in front of a couple hundred

Sorry, Paul.  It is not at all your fault that you didn't know what
this amorphous "site" thing is, and I apologize for blindsiding you
in the meeting.  (Though I *was* hoping to blindside you with
the flaw I found in your proposal, but you deprived my of that
pleasure by discovering it yourself.  :-)

The lack of a proper description and common understanding of what
"sites" are is indeed a serious oversight (no pun intended).  I sort
of assumed that people would understand what was intended from the
normal English meaning of the word "site", as in building site or
job site.  But that was clearly a flawed assumption on my part.
Perhaps the more recent jargon term "web site" has muddied the
connotation?

>think the burden is on you to point me to this illusive piece of text that

The "IP Version 6 Scoped Address Architecture" draft, the most recent
version of which is draft-ietf-ipngwg-scoping-arch-02.txt, contains
the best definition so far, buried in an itemized list of the three
unicast scopes (in Section 4):

           o Site-local scope, for uniquely identifying interfaces 
              within a single site only.  A "site" is, by intent, not 
              rigorously defined, but is typically expected to cover a 
              region of topology that belongs to a single organization 
              and is located within a single geographic location, such 
              as an office, an office complex, or a campus.  A personal 
              residence may be treated as a site (for example, when the 
              residence obtains Internet access via a public Internet 
              service provider), or as a part of a site (for example, 
              when the residence obtains Internet access via an 
              employer's or school's site). 

I have a hunch that you, and probably many others, will still find this
description less than satisfying, preferring a simple, concrete rule for
defining a site, but perhaps you can at least get a glimmer of the
general notion that has been mostly buried in my mind and inadequately
documented so far.

Steve

---

From: Joe Abley <[email-masked]>
Date: Sat, 24 Mar 2001 09:56:21 -0500

> baffled---and it isn't fun to be baffled in front of a couple hundred

Steve's reference notwithstanding, I don't really understand why it helps
to have a site defined in (admittedly vague) geographic terms, as opposed
to referring only to network topology.

Seems to me that the geographic reference just adds confusion, since there
will always be cases where it is perfectly legitimate to consider a network
which spans cities (or countries, or continents) a single site.

The fact that the majority of sites might fit within a single building or
residence only seems relevant if there is some technical reason for
delineating a subnetwork based on geography (and if there is, I'm not
seeing it :)

Joe

---

From: Robert Elz <[email-masked]>
Date: Sun, 25 Mar 2001 17:54:33 +1000

Date:        Fri, 23 Mar 2001 20:08:43 -0800
    From:        Steve Deering <[email-masked]>
    Message-ID:  <v04220802b6e1c6d1bdbb@[10.83.97.214]>

  | I have a hunch that you, and probably many others, will still find this
  | description less than satisfying, preferring a simple, concrete rule for
  | defining a site, but perhaps you can at least get a glimmer of the
  | general notion that has been mostly buried in my mind and inadequately
  | documented so far.

I find it less than satisfying, but not for that reason, in fact, for
exactly the opposite reason, that definition is far too precise.

A site should be whatever I want it to be.   About the only requirement
should be that it is internally connected (somehow, including using tunnels).

No more than that is needed - it is just a collection of nodes that the
administrator defines are a site, and then configures the routers at the
borders of the collection of nodes to mark them as site boundary routers.

I can't imagine why any relationship with buildings, geography, campuses,
or anything else like that should be necessary - they add nothing.

Just as the routing architecture, etc, don't impose any requirements on
just what the thing is that gets a /48 routing prefix, beyond that it needs
to be a connected network, we also don't need any specific definition of
what is a site - all that can possibly do is to constrain thinking into
the future.

kre

---

From: Randy Bush <[email-masked]>
Date: Sun, 25 Mar 2001 13:50:19 -0800

so all <name of arbitrary big isp>'s global backbone, aggregation, and
servers are one site?

randy

---

From: "Paul Francis" <[email-masked]>
Date: Mon, 26 Mar 2001 01:17:14 -0800

> pleasure by discovering it yourself.  :-)

The latter would've been ok.  One deserves to be blindsided with ones own
flaws.

I think it wasn't so much the blindsiding that bothered me, but the fact
that, unknown to me at the time, you continued to use the word "site" in its
common English sense rather than in the rigorous sense I was assuming.  It
should have been clear to you that I was attempting to speak in a rigorous
sense (like when I suggested that two office networks in two cities
connected by a dedicated link with only a single ISP connection surely would
be considered a single "site" in the networking sense.  Obviously at that
point in time we couldn't have been discussing the dictionary meaning of the
word "site".)

Anyway forget about it...apology appreciated and accepted.

Thinking back, I remember you started that thread with the statement that
many people equated a site-local with an IPv4 net-10 address, and that this
was incorrect.  Other than the fact that an individual site-local address
has a higher probability of being globally unique because of the EID field,
what else is different?  I can't re-create your argument in my head.

By the way, I can certainly see that nailing down the definition of "site"
would be difficult.  I think the problem is that we use site in two
different contexts:  One for "site-local", and the other for SLA (Site Level
Aggregator).  It is not necessarily the case that the boundaries of a
site-local "site" match those of a globally aggregatable SLA "site".  In
fact, I suspect that if you decoupled the assignment of SLAs for a
site-local prefix from that of SLAs for a globally aggregatable prefix, you
could in fact achieve smooth renumbering when merging two "sites" (if you
had near-unique site-local addresses).

But I'll save that for version two of the internet draft.

PF

---

From: Margaret Wasserman <[email-masked]>
Date: Sun, 25 Mar 2001 21:54:07 -0500

Hi Steve,

>general notion that has been mostly buried in my mind and inadequately

If I understand correctly, you will also be adding another
restriction to the definition of "site" -- specifically that
the routing structure of site (and/or a link) must be
"convex".  That is to say that the shortest routing path
between two nodes within the site must stay entirely within
the site.

This restriction is required in order for the packet sending
rules defined in the scoping architecture to be correct.

Right?

Margaret

---

From: "Brian Haberman" <[email-masked]>
Date: Wed, 28 Mar 2001 10:53:19 -0500

Margaret,

> rules defined in the scoping architecture to be correct.

Yes.  I have made a note to add this to the document.

Brian