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Re: Multi-6 [WAS: OT - Vint Cerf joins Google]
- From: Daniel Senie
- Date: Tue Sep 13 14:59:59 2005
At 10:17 AM 9/10/2005, Joe Abley wrote:
Could the IPv6 proponents get their stories straight?
On 10-Sep-2005, at 09:18, Patrick W. Gilmore wrote:
[Perhaps this thread should migrate to Multi6?]
multi6 hasn't existed for some time. The "level-3 shim" approach to
multi-homing that was the primary output of multi6 is being discussed
Suppose they not only have no plan but couldn't really put together
a plan to support 200 customers? Does this mean Google, or any
other content provider, is "unworthy" of globally routeable space?
Yes, according to the current RIR policies. [So the determination of
"unworthy" above has been made, in effect, by RIR members.]
IPv6 is a nice idea, and as soon as people realize that ISPs are
not the only organizations who have a need to multi-home - and I
mean really multi-home, not stupid work-arounds - then it might
actually start to happen.
It's not as though this line of thinking hasn't been followed many,
many times before. The counter-argument goes like this:
1. There is more v6 space than there is v4 space, by virtue of the
fact that the address is 96 bits wider.
On the one hand, the talk is of 128 bit address space, then on the
other hand the talk is of security-by-obscurity by handing out /48's
to everyone and having networks really sparsely populated. So given
the address space is so massive that 1/2 of the bits are effectively
a local subaddress, perhaps the talk should be of doubling the number
of bits, not quadrupling. Yes, I understand you can slice and dice
however desired, but it sure seems like the proponents play fast and
loose with the numbers when making their arguments, and it's tiresome.
The rules today have not resulted in and overly huge number of
multihomers. The IPv6 crowd evangelists on the one hand insist
there's no need for NAT, while on the other hand provided no solution
to multihoming, and what's been evolving in the various "fixes" for
that are less palatable than running a multiport NAT box. The choice
is simple: live with NAT or provide portable address space. The
marketplace is not likely, IMO, to accept shim6.
2. Because there is vastly more v6 space than v4 space, if
entitlement to PI space in v6 was opened up the chances are many more
people would have v6 PI space than currently have v4 PI space.
End systems should not be making decisions on where packets go beyond
the local network segment. This has been tried before. It was called
Token Ring Source Route Bridging. It was a bad idea then, and it's a
bad idea now to have end stations deal with routing. SRB came into
being to save the network elements from the burden of keeping track
of the functioning of the network. Then Ethernet switches came along,
spanning tree, and so forth.
That's true today. Router memory complement has increased over time.
So what? Cost of processing power and memory are a tiny fraction of
what they were when the routing table was in the 20,000 prefix range.
3. Every PI assignment/allocation takes up a routing slot in every
router in the DFZ.
Processors in current routers are well below the fastest on the
market. There's plenty of horsepower headroom. There's plenty of
opportunity to expand the amount of memory.
4. Given 2 and 3, there is potential for the amount of state in the
DFZ to exceed the capabilities of the network to hold and process it
(e.g. enormous RIBs, soaring processor requirements for dealing with
What floodgates? Are we flooded today? The rules today for getting
portable space are NOT all that difficult to meet.
It's possible that the number of PI assignments might not be that
high, and the scaling properties in practice might not be so bad.
However, you only get to find this out after you've opened the
floodgates, and if it turns out that it doesn't scale, it's hard to
push the water back into the reservoir.
That multihoming was not properly addressed as a core goal to solve
in IPv6 is one of the failings in the whole effort. The shim6
approach is, IMO, not going to fly. A multiported NAT box for $179 or
less (present product in the marketplace) provides a simple solution
without the end stations being involved. Sure, it uses NAT.
The goal in shim6 is to find a mechanism which provides all the
functional benefits of multi-homing without holding all the state in
There seems to be some ongoing perception that various protocol/
research organisations have no idea about the value of multi-homing
Sadly, because folks wouldn't listen then, IPv6 lacks a useful
multihoming solution beyond what we have in IPv4. Gluing on band-aids
is not going to solve it. Relying on Moore's Law to continue to make
routing equipment keep up is going to be a necessity.
for enterprises in the real network, and hence ignore it. While that
might have once been the case (I certainly remember thinking so
around 1997 whilst shouting on the ipng list), I don't believe it's
the case today.
Correct. And so we will see multiport NAT boxes for the forseeable
future for smaller sites, and PI space for larger ones.
The real problem is that there is no simple answer that doesn't have
potentially nasty consequences.