On Wed, 19 Jan 2005 19:16:44 +0000, Toad <[EMAIL PROTECTED]> wrote: > Are you saying that hosts are required to support MTUs of at least 576 > bytes? People have said that some dialup connections use 256 byte > MTUs...
Hrm. Dialup. The MTU includes the PPP header is max. 30 bytes, IP header can be a maximum of 60 bytes and UDP is a further 8 bytes.. That's 98 bytes of header, leaving 158 bytes of data. So the header is 38% of the packet? That sounds absurd... Of course, PPP can use header compression on the PPP and IP headers, leaving the PPP header at ~4 bytes and IP at ~20, leading to a 38 byte header (14%), but it's still a small packet, considering that an uncompressed header set over an ethernet (1500) MTU is 6%. On Windows the lowest possible MTU is apparently (http://techrepublic.com.com/5100-6268-1061241.html) 68 bytes, but that's absurd. Since you're supposed to send 576 byte packets anyway if PMTU discovery doesn't work then I'd go for that figure. If things start dropping, or more likely the client's ISP starts sending must-fragment ICMP packets, then throttle back. Of course, if the computer you're trying to connect from has a stupidly low MTU, AND a stupid firewall that blocks incoming ICMP then the user really deserves what they're getting. I've been known to be particularly unpleasent to individuals who think blocking an essential control protcol is a good idea. -- Phillip Hutchings http://www.sitharus.com/ [EMAIL PROTECTED] / [EMAIL PROTECTED] _______________________________________________ Support mailing list Support@freenetproject.org http://news.gmane.org/gmane.network.freenet.support Unsubscribe at http://dodo.freenetproject.org/cgi-bin/mailman/listinfo/support Or mailto:[EMAIL PROTECTED]
