[e2e] 100% NAT - a DoS proof internet

Joe Touch touch at ISI.EDU
Mon Feb 13 08:18:04 PST 2006

Hi, Jon,

Jon Crowcroft wrote:
> So there's three things here
> 1/ a mad idea for a DoS proof internet - This goes like this:
> What if 100% of hosts were behing a NAT (a bit like mark handley and
> adam greenhalgh's idea on a dos proof internet in fdna a while back, 
> but taken to extreme, or also like default off paper in hotnets)
> So how would you ever reach someone (like most NAT traversal stuff is
> tricky - viz skype - see also below:)
> Meanwhile, here is how: Distributed Hashed Time.
> So we all know about DHTs - they hash an object to a node id, then use
> some p2p route to get to the node id (e.g. MIT's chord finger table
> etc etc).
> So if we want to talk to a set of known people, we hash their
> identifier (name) to TIME. We then send to each other at that agreed
> time - no-one else can send to us or from us to them, and the hash key
> can be a shared secret....

How do you "send to each other"?

You need to talk to a host behind a NAT. You need to reach the service
on that host that runs this DHTime protocol. You can have more than one
host behind the NAT. A NAT basically makes everything behind it look
like one host.

There are two options:

	a. the host behind the NAT tries to reach the other host first
		this works only if the 'other host' is NOT behind
		a NAT, so we're out of luck

	b. you 'register' your host somewhere as owning a unique
	way to demultiplex packets to it

A DHT does both of these - (a) to reach a node somewhere else that is
NOT NAT'd first, then (b) to register in that infrastructure so other
nodes can find it using its node ID.

Two killer questions:

	1. if everything is NAT'd, how do you perform step (a)?
		i.e., where is the first place you register?

	2. (b) assumes hosts have unique node-IDs, but you
	went through a lot of trouble to remove that property (NATs)

		for every reason you had a NAT in the base net,
		why is it now acceptable to not NAT the node-IDs?

		- if you NAT node IDs, you're back where you started

		- if you're OK with not NAT'ing node IDs, why did you
		NAT the base net?
			i.e., non-NAT'd node IDs now become susceptible
			to every message on the DHT

> there you go...the details should be simple (apart from how you
> provide sufficiently accurate synchronized time without a globally
> reachable adddress betweewn the NTP servers, which, I admit, is
> probably a mite tricky - i guess you need to have them agree a set of
> rough times or something:)

Time, IMO, is the least of your concerns...


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