ibuprofin

1191 Path MTU discovery. J.C. Mogul, S.E. Deering. November 1990.
(Format: TXT=47936 bytes) (Obsoletes RFC1063) (Status: DRAFT
STANDARD)

1435 IESG Advice from Experience with Path MTU Discovery. S. Knowles.
March 1993. (Format: TXT=2708 bytes) (Status: INFORMATIONAL)

2923 TCP Problems with Path MTU Discovery. K. Lahey. September 2000.
(Format: TXT=30976 bytes) (Status: INFORMATIONAL)

The problem has been known for a "few" years, but it still catches people by surprise.

0791 Internet Protocol. J. Postel. September 1981. (Format: TXT=97779
bytes) (Obsoletes RFC0760) (Updated by RFC1349) (Also STD0005)
(Status: STANDARD)

top of page 8, and 'figure 4' (counting from zero, bit 48 is the "Don't Fragment" flag).


RFC1435 and RFC2923 above. Someone is dropping ICMP Type 3 Code 4,
probably as a "security issue" to deter the wily hackers. (Most
Linux networking stacks are compiled to default to using the DF flag,
and you can easily see this using a packet sniffer.) There was a
similar problem when the 2.4.0 kernel was introduced in January 2001
involving the ECN (Explicit Congestion Notification). Some routers
were silently dropping packets when that flag was set in the TCP
header. "A fix" was to disable this feature in the Linux kernel
(echo 0 > /proc/sys/net/ipv4/tcp_ecn) but the real solution was for
the owners of those routers to get their software up to date.

Old guy

adam

I think Jim Beard is running Verizon FIOS. I'm running Verizon DSL
through the modem/router they supplied. I set up my connection thru mcc
as DSL and left it at DHCP and it works, so I guess I'm not using pppoe.

On my system, with Mandriva 2008.0 I couldn't get to the website in
question with the default MTU of 1500, but succeeded with MTU at 1488 or
less. Using VMware under Mandriva 2008.0 to run Win2K, there was no
problem even with MTU still 1500. I don't quite understand why.
Anyway, I hope something in here answers your query.

Adam

marc paré

Marc Paré a écrit :

Thanks for notes everyone.

I am just a little confused now.

So, should the fix be coming from the website admins or is the fix left
up to the individual users who would then have to tweak their MTU?

Marc