On Jun 25, 2007, at 09:33, Templin, Fred L wrote:
I already gave my use-case in:
http://www1.ietf.org/mail-archive/web/ipv6/current/msg07806.html
The use-case I am most interested in is Mobile Ad-Hoc Networks
(MANETs) in which two or more MANETs can merge (e.g., due to
mobility). If each MANET used ULA-C's, then they could inject each
others' prefixes into their IGPs with no opportunity for
collision. If each MANET instead used RFC4193 ULAs, then they
could *probably* still inject each others' prefixes. But, however
small the risk of collision, RFC4193 ULAs still have one drawback
that ULA-C's do not - uncertainty.
So perhaps another question is whether it is too much to ask for
more certainty (ULA-C) and less mystery (RFC4193 ULA)?
The "no opportunity for collision" thing is really the question here,
as Brian E. Carpenter said in <http://www1.ietf.org/mail-archive/web/
ipv6/current/msg07834.html> and others have said elsewhere. Most of
the pushback is directed at this claim that central registration has
some hope for mitigating an already *epsilon* risk of collision. I
don't think simply reiterating the claim is an appropriate response
to the legitimate rebuttal it's received.
An additional claim we've seen is that ULA-C should offer reverse
delegations from ip6.arpa in the public DNS horizon, whereas ULA-L
(straight RFC 4193) does not. Your use case does not seem to me to
support the argument for ULA-C, but actually demonstrates its weakness.
When two MANET merge by exchanging ULA prefixes (let's forget about
ULA-C vs. ULA-L for now, because the name resolution problem is
common to both), then their DNS horizons must be merged as well. The
networks are *ad-hoc*, so they do not have name servers provisioned
with globally reachable unicast addresses. If they did, then they
wouldn't be *ad-hoc* mobile networks. They'd be *provisioned* mobile
networks.
So, the two MANET may have name servers, but if so, then they're only
reachable at ULA addresses and they contain records that are only
usable inside the merged MANET. What you need to do is exchange the
reverse delegations for the ULA prefixes at the same time you
exchange the prefixes. You already have to merge two private DNS
horizons into a single private DNS horizon. Asking for help from the
public DNS horizon seems like a very questionable thing to propose.
Looking up the AAAA records containing ULA-C addresses for the peer
MANET name servers in the public DNS horizon is prohibitively
expensive for the usage scenario you're proposing. Let me
illustrate. Who will operate the authoritative name servers for the
global public 0.0.c.f.ip6.arpa domain? How will mobile *ad-hoc*
networks get NS records inserted into that zone? How are they
changed? How will registrations be released and made available for
reuse? Do registrations expire if you don't pay your bills on time?
Perhaps most importantly, how do MANET remain *ad-hoc* given such
provisioning requirements? All those questions seem to be pressing
and unanswered.
(p.s. I have long contended with my colleague, Stuart Cheshire, that
Multicast DNS could use to be extended to support organization-local
scope multicast, precisely to support ad-hoc ULA-addressed
internets. Alas, there hasn't been much perception around here of
any burning need to do it-- the subject of rendezvous points always
comes up, and nobody has time to come up to speed on all the latest
technical aspects of the problem. Perhaps additional energy should
be expended there toward those ends?)
--
james woodyatt <[EMAIL PROTECTED]>
member of technical staff, communications engineering
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