Subject: how many locators?

From: Andrew Partan <[email-masked]>
Date: Thu, 13 Nov 2003 15:47:33 -0500

How many locators should hosts have - or - how big is the global
routing table - or - where do you get your locators from?

As the number of locators per host goes up, the complexity of
choosing a pair of locations to use for a onnection goes up even
faster (probably as n**2).

So we probably want to limit the number of locators per host to a
smallish number.

Now hosts end up getting their locators from their upstreams (and
their upstreams' upstream?).  The question is how far up you go.
The further up you go, the more local paths out you have (probably
on the order of n**2), so the more locators per host you have.

If you go to the upstream's upstream's upstream, then you are
approaching approx the Tier-1 core, so the size of the global routing
table is approx the size of the Tier-1 core -- but at the cost of
having lots of locators per host.

If you go just one hop to the upstream to get the locator, then you
have just a few locators per host (basically the number of transit
connections per site), but you have a much larger global routing
table - approx the number of ISPs in the world.

Is this a reasonable size with reasonable growth factors?
	--asp

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From: Brian E Carpenter <[email-masked]>
Date: Thu, 13 Nov 2003 23:04:15 +0100

Andrew Partan wrote:
...
> table - approx the number of ISPs in the world.

This is the model I have always assumed for IPv6.

> Is this a reasonable size with reasonable growth factors?

This is what I have assumed.

If these assumptions are false, I think it affects more than just
multi6.

   Brian

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From: Iljitsch van Beijnum <[email-masked]>
Date: Thu, 13 Nov 2003 16:25:54 -0600

> faster (probably as n**2).

Actually at some point the complexity goes down again. If we take 
getting an address from each ISP to its extreme at some point hosts 
will have addresses for each aspect of our existence. So at some point 
two people at opposite ends of an ocean are each going to have an 
address from the provider of the intercontinental cable. The regular 
"longest match first" rule in the address selection mechanism will then 
select those addresses for both ends. Then we simple add a preference 
to each address and it's going to be the best possible address, too.

But in reality the average number of addresses for multihomers would be 
very close to 2, exactly because having many addresses would stress the 
selection mechanisms (that we have to come up with) too much.

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From: Masataka Ohta <[email-masked]>
Date: Fri, 14 Nov 2003 08:08:12 +0900

Andrew Partan;

First, thank you for initiating a real engineering discussion,
with quantatative analysis possible.

> How many locators should hosts have

At Vienna, I said 9 (=3*3) is a proper upper limit.

> - or - how big is the global
> routing table

1K~8K.

> - or - where do you get your locators from?

Anyway, though DNS is suggested.

> faster (probably as n**2).

No. It is n. We have code of our protocol to do so.

Moreover, global routing table small enough to be held on hosts
can optimize the order of try that n can, in most cases, 1 or 2.

> So we probably want to limit the number of locators per host to a

Still yes, though 16 or 20 may be tolerated.

> their upstreams' upstream?).  The question is how far up you go.

Two levels of ISP is reasonable.

But, note that lower level ISPs can peer with a lot more than
3 other ISPs.

A site may directly negotiate with upper level ISPs to have
9 upper links.

Depending on a policy to assign TLAs, big companies may get
its own TLA and be multihomed with IPv4 style. But, it should
cost a lot.

> having lots of locators per host.

The cost should be paid by those wanting to have lots of locators
or their peer.

> Is this a reasonable size with reasonable growth factors?

Currently, ISPs are assigned address blocks, primarily if they
are multihomed to other ISPs, which is inevitable with multihoming
issues unsolved.

As the number and density of ISP grows, more and more ISPs qualify
to have its own address blocks. Note that, with dark fiber, cost
of local peering is almost zero.

Suppose that an ISP, in average, serves 1K people mostly singly
homed and world population is 5G, there will be 5M ISPs.

Do you think it small enough?

						Masataka Ohta

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From: Brian E Carpenter <[email-masked]>
Date: Fri, 14 Nov 2003 03:40:20 +0100

Masataka Ohta wrote:

<snip>

> homed and world population is 5G, there will be 5M ISPs.

I think 1K subscribers is a very low average. Even 10k seems low to me.
So I think 500k ISPs is more likely than 5M.

   Brian

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From: Masataka Ohta <[email-masked]>
Date: Fri, 14 Nov 2003 20:45:25 +0900

Brian;

> I think 1K subscribers is a very low average.

In countries, such as GB, where PTT is still strong, maybe,
it is.

But, we are talking about the future.

It won't, or, at least, it is safe to assume it won't.

Note also that I assumed people will use ISPs not only
as home users but also as mobile and corporagte users.

> Even 10k seems low to me.

Just 4 or 5 times more than the current number of routes?

It, surely, is too optimistic.

Moreover, even it costs a lot, not only for memory and bandwidth
but also for operational costs such as BGP convergence time,
possibility of route flapping, possibility of bogus route
and so on. 100K is already too much.

						Masataka Ohta