[ppml] IPv4 swamp, mh end-users & IP architectural solutions: LISP/APT/Ivip

Robin Whittle rw at firstpr.com.au
Sun Aug 19 22:03:35 EDT 2007

In "Re: [ppml] Policy Proposal: IPv6 Assignment Guidelines" Brian
Dickson wrote, in part:

> The *only* problem with the IPv4 swamp, was that there were
> multiple assignments to ASNs, that couldn't be aggregated by the
> ASNs. If we place up front, the requirement that all assignments
> must always be aggregateable, by virtue of the fact that there
> isn't anything to aggregate, the problem never comes into
> existence.
> There will undoubtedly be cases of acquisition and mergers, where
> as a consequence of the joining of ASNs, that a single ASN has
> more than one PI block.
> But, if the rule is "once you *have* a block, you can't request
> another", rather than "you're only allowed one at any point in
> time", the result is suitably similar - growth only occurs at the
> rate of ASN assignments, which are gated by the rate at which new
> multihomed-via-BGP networks enter the DFZ universe.

I disagree with the statement that the only problem with IPv4
routing is that some or many end-user networks (or ASNs in general -
providers and end-users combined) have more than one BGP advertised
prefix which are numerically separated and so can't be aggregated
into a single advertised prefix.  There are also problems with
stability, excessive updates for some prefixes and the projected
growth in the number of end-user networks which must be multihomed.

I believe the same problem will afflict IPv6 if and when it is
widely adopted, now that ARIN, AfriNIC and RIPE are assigning /48s
of PI space to end-users.

My understanding of the consensus on ROAP (Routing and Addressing
Problem) is that the biggest single problem is the inability of the
BGP control plane to cope with the growth in the number of
multihomed end-user networks, which could reach into the millions -
even if every network only had one advertised prefix.

The discussions on the RAM list, resulting from the IAB RAWS
workshop last year:


lead me to think that the currently proposed solutions are of two
types.  Firstly, moderate improvements to BGP to improve stability
and therefore to reduce some of the problems of having more and more
advertised prefixes.  Secondly, a "locator-ID" separation scheme
involving tunnel routers, a mapping database etc. at the IP level to
enable multihoming, traffic engineering and what I call "portable
address space" for large numbers of end-user networks, without each
such network adding to the number of BGP advertised prefixes.

The schemes for doing this are LISP-NERD, LISP-CONS, eFIT-APT and my
own proposal Ivip:  http://www.firstpr.com.au/ip/ivip/ - which also
supports mobility with nearly optimal path lengths for IPv4 and IPv6.

It seems that a scheme such as one of these will be required,
despite the fact they are all kludges with significant problems due
to tunneling overhead, MTU limits -> fragmentation, disrupting Path
MTU Discovery etc.

All this effort is based on the notion that the problem is with the
future number of end-user networks requiring multihoming - and that
even if each required only a single advertised prefix there would
still be such a scaling problem that some drastic architectural
change (LISP/APT/Ivip etc.) would be required.

 - Robin

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