kre, | Alain Durand wrote: | Reachability os one thing, but you may have to wait for TCP timeouts. | RFC1122, section 4.2.3.5 TCP Connection Failures | Says that the initial SYN has to wait at least 3 minutes...
> kre wrote: > You're assuming that I am actually using a TCP SYN to > detect reachability. That isn't the way it is done. We want > to make things work well, not arbitrarily slow them down. The problem is that the only way to _really_ test reachability is to actually try. For example, if you can successfully ping a host it does not mean that you can telnet to it (or the opposite: ICMP might be blocked and it might be the best path). Or if you can open an http connection on port 80 it does not mean that you can open an https one on port 443 (because someone forgot to open the port) or the opposite (because the network administrator wants to enforce an https-only web server). Note that I am not suggesting that the reachability discovery should be application specific, but OTOH I don't really see how it can't be. There might be a slippery slope that says to reduce the SYN delay, but I'm not buying into it. Look at SMTP for example: if you open a connection on port 25 to my mail server it is going to check your IP against a number of spam lists before returning the ACK. This takes time; if we put 100ms here it is broken. What Alain refers to is one of the reasons I stated earlier that we will continue to see split or dual-headed DNS, because if an app uses TCP as the transport mechanism, we are looking at either a SYN to detect reachability or at an app failure because the reachability detection mechanism used ICMP or UDP. In either case, we are looking at unacceptable delay. Delay leads to frustration. Frustration leads to split-DNS. Michel. -------------------------------------------------------------------- IETF IPng Working Group Mailing List IPng Home Page: http://playground.sun.com/ipng FTP archive: ftp://playground.sun.com/pub/ipng Direct all administrative requests to [EMAIL PROTECTED] --------------------------------------------------------------------
