Re: soft state (was Re: shim6 and bit errors in data packet headers

[marcelo bagnulo braun <marcelo@it.uc3m.es>]

Hi Iljitsch,

El 14/05/2005, a las 14:46, Iljitsch van Beijnum escribió:
> > The above assumption is based in that i think this is needed to 
> > properly protect from flooding attacks.
> > I mean, the goal of reachability tests in a shim protocol can be 
> > two-folded:
> > - to explore if a given address pair is working
> > - to determine if a given host is willing to receive packets at a 
> > given address (i.e. to prevent flooding attacks)
>
> > the first goal can be achieved with a kind of ping (enhanced ping in 
> > order to determine unidirectional reachability) but it may not 
> > require that the reachability test is associated with a given 
> > context. I mean, the goal here is just to obtain reachability 
> > information
>
> > The second goal is somehow different, and since what is being queried 
> > is the willingness of the node to receive traffic through a certain 
> > address, it is needed to inform the node which traffic are we talking 
> > about.
>
> The thing is, that you need some kind of semi-reliable communication 
> to accomplish all of this, and to do the negotiation too. (In the case 
> of the reasability testing, it would be useful if the receiver of a 
> probe would have a semi-reliable way of telling the sender that the 
> probe was received.) There is also some circularity: you need 
> connectivity to negotiate locators, but you need to know the locators 
> already to discover connectivity.

Well, i was thinking in retrying a couple of times, just to keep it 
simple. I don't know yet if this would provide all that we need though

> I'm thinking we could come up with a kind of "UDP on steroids" that 
> similarly to SCTP works over multiple addresses. Such a semi-reliable 
> multi-address datagram protocol would be very useful for the 
> negotiations and similar exchanges, and it would supply reachability 
> information as sort of a by-product.

this sounds quite more complex that what i was thinking about... (maybe 
it only sounds complex though :-)

> Separating this layer also has the advantage that a simple unprotected 
> multi-address datagram protocol can be used for other purposes as 
> well, and it allows us to layer the solution so that we can work on 
> different aspects independently.
>
> > :-)
> > Context state AND path failure AND unidirectional connectivity.... 
> > this seems amusing enough
>
> Since the situations where context state doesn't exist (= before the 
> start of a session) and unidirectional reachability (caused by ingress 
> filtering) will be very common, we really need to cover this case.

I guess this depends on what solution for ingress filtering 
compatibility is available i guess

Regards, marcelo