Multi-6 [WAS: OT - Vint Cerf joins Google]

Sat Sep 10 14:17:55 UTC 2005

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  
in shim6.

> 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.

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.

3. Every PI assignment/allocation takes up a routing slot in every  
router in the DFZ.

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  
updates, etc).

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.

The goal in shim6 is to find a mechanism which provides all the  
functional benefits of multi-homing without holding all the state in  
DFZ routers.

There seems to be some ongoing perception that various protocol/ 
research organisations have no idea about the value of multi-homing  
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.

The real problem is that there is no simple answer that doesn't have  
potentially nasty consequences.

Joe