On Thu, 4 Feb 2010, Robin Whittle wrote:
All that is happening with IPv4 is that the last fresh paddocks of
unused land are now being built upon. There's plenty of scope for
squishing houses closer together - and then for building multi-storey
houses (NAT). Without NAT, some kind of crunch would occur with
IPv4 if there was ever a need to connect more than about 3 or 3.5
billion hosts at any one time. With NAT, there's no limit.
NAT is not the ideal of any-to-any Internet connectivity, just like
the crowded suburbs with multi-storey dwellings don't provide all the
benefits of living in an uncrowded piece of countryside. But just as
crowded cities get more crowded, so will IPv4. The attraction is the
same for cities as for the choice of which Internet use - most people
want and need to be where all the other people are.
If we're thinking in terms of analogies, it's important to note where
they break down. The "build up, cause can't build out" analogy breaks
down in 2 ways:
1. Earth isn't Trantor yet, many urban areas are still expanding.
(Indeed, in europe, urban areas in many cases have gotten /less/
crowded precisely through outward expansion and rehousing people
from congested slums of the industrial revolution to developments
and "new towns" in the country side, what we know think of as
suburbs.)
2. There is no definite limit to building up, though it does
become more costly to engineer whereas there are definite limits
to 'building up' in IPv4.
I.e. we /can/ make bigger and bigger buildings, for a given
footprint. Whereas there are fixed, fundamental limits to IPv4
that hard-constrain how many of todays ULPs can go through.
You might respond that the internet would adapt by changing the ULPs
to better make use of IPv4. E.g. we could make NAT friendly
transport protocols:
- Add a "Internal host ID" field to ULP headers, like TCP.
- Increase the range of the flow^Wport ID
So that a transport address on the internet then becomes some kind
of 3 tuple:
(public IP of the concentrator, network specific host ID, flow/service ID)
The core internet routing tables are then constrained to O(|public IP
space|).
Concentrators can be stateful or stateless at their discretion. If
concentrators are stateless, you could even have anycast
concentrators and have a number of concentrators service a single
concentrator ID.
So basically, your argument is that the locator/identifier split
should be done by changing transport protocols - retaining IPv4
compatibility - rather than done by shimming something in to make it
all transparent to ULPs (map and translate/encap).
I have to say, I kind of agree that changing the transport is the
best way to go in the long run. It's simpler than map-encap and it
seems we could as easily upgrade the transport layer on the internet
as we could move the internet to IPv6 (needed for some map
translate/encap proposals). Plus, it'd work with either v4 or v6.
Anyway, I guess I'm stating the obvious :)
NB: The upper-layer adaption could also be done without touching the
transport layer, through higher-level application specific
multi-plexing. But then we definitely no longer have anything
resembling the internet, and I assume no one here wants that.
regards,
--
Paul Jakma [email protected] Key ID: 64A2FF6A
Fortune:
"The medium is the massage."
-- Crazy Nigel
_______________________________________________
rrg mailing list
[email protected]
http://www.irtf.org/mailman/listinfo/rrg
