Re: address pair exploration, flooding and state loss

[Iljitsch van Beijnum <iljitsch@muada.com>]

On 27-mei-2005, at 16:35, marcelo bagnulo braun wrote:

> > However, it gets even better if we also include ids and address  
> > pair info for probes we recently sent or maybe even are about to  
> > send.

> i don't see how this is useful... see below

> > So if A sends out 6 probes using 6 address pairs and puts a  
> > "manifest" for the whole batch of probes into each of them, then B  
> > can, after waiting a bit, determine that there is reachability  
> > from A to B for 3 pairs and, presumably, unreachability for the  
> > other 3 pairs. B then includes this information in its replies to  
> > A and A then knows exact reachability information for all address  
> > pairs in the A -> B direction. (Well, probably want to send more  
> > than one probe per pair when you need to be absolutely sure.)

> the relevant information here is that B send A what probes B has  
> received. A informing B about whta probes A sent does not provide  
> any help, AFAICT.

You're mostly right: it doesn't provide the benefits I thought it  
would: B doesn't really need to know about reachability from A to B,  
and A can already determine from what it knows it sent and what it  
gets back from B what doesn't work in the A -> B direction.

However, if we assume that bidirectional connectivity is the most  
common, the fact that A sent something and B didn't get it is a good  
hint for B that this address probably won't work in the opposite  
direction either.

Since we want to arrive at one or two "good enough" pairs as quickly  
as possible, such hints could be valuable.

Something else:

Sometimes, the sender may want to receive a positive reply  
immediately, while in other cases it may prefer that the other side  
wait for a while and send a report that covers a number of probes.  
Most likely: A sends some probes to B, and it wants an immediate  
reply from B when B receives the first probe, and then a second reply  
for all the other probes after sufficient time has passed for B to  
have received them all.

It's probably useful to include a field that governs the reply  
immediacy.