Subject: [RAM] Re: server referrals

From: RJ Atkinson <[email-masked]>
Date: Wed, 31 Jan 2007 10:32:40 -0500

Earlier Thomas Narten wrote:
> IMO, this assertion needs to be shown to be true.
> I suspect its very much not.

Well, if one is looking to prove assertions, let us please start
with proving the unsubstantiated assertion that server referrals
necessarily are broken by moving to an ID/Locator split.

I've asked for a concrete example of a case where server referrals
would be broken.  So far, not one single concrete example has appeared
on this list and there's been ample time.

Now on that point, let me observe that anything that works today
with an "address" can trivially work going forward with an I/L
architecture, since an "address" is merely the combination of
an "identifier and a locator".  To give a trivial example from
O'Dell, and this is MERELY one example, the same 128 bits would
get passed around for existing IPv6 or I/L split IPv6.

In fact, SHIM6 would have challenges in this area if anything did,
because an application only knows the "IPv6 address misused as
Identifier" value and does not knwo the "IPv6 address used as locator"
value.  So the application (or even the transport-layer) would
not know the "locator" value to pass to the other end in the referral.
Despite this issue, SHIM6 seems to have some IETF support and
"server referrals" don't seem to be a barrier to SHIM6 standardisation.

> A few years back, I was dealing with a sysadmin that blocked ssh
> logins from IP addresses for which there was no reverse DNS mapping. I
> found that when I was on the road, I often couldn't log in.  When
> talking about this with some folk at (I believe) RIPE, they observed
> that the reverse tree was becoming less and less usefully
> populated. I'm pretty sure there is data around about this from folk
> that walk the tree as part of checking delegations and such

Clearly your experience and mine vary.  It is useful to understand
that there are a range of data points.  Certainly for the (US, JP,
and EU) places where I can check existence of reverse DNS, it is
there in all cases.  It is generally of the form I described before,
in the ISP's chunk of DNS, rather than having PTR records being
in some end-user's domain -- no surprise since my example was
with residential broadband ISPs rather than with a commercial service.
For commercial services, my employer has had no problems getting
suitable forward and reverse DNS entries -- even for globally routable
IP addresses that belong to our sundry uplinks.

(Internally, by policy, we always use private addressing and NAT,
which actually works fine for our uses, as near as I can tell.)

Yours,

Ran

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From: Geoff Huston <[email-masked]>
Date: Thu, 01 Feb 2007 12:32:39 +1100

>"server referrals" don't seem to be a barrier to SHIM6 standardisation.

I'm reluctant to get into a digression into the details of the shim6 
approach, but the characterization above is not exactly correct in 
that the shim6 referral token is the initial locator, which is(*) a 
valid locator, and in this model the referral mechanism is no 
different to the way things happen today.

(*) my description is also not quite correct here, and there are 
failure cases for the referral token that could only be resolved back 
into a candidate locator set by a backward and then a forward DNS 
query pair, but unless folk want me to dive further into details I'll 
leave the description at this (terse) approximation.

Geoff