On Wed, Mar 19, 2008 at 12:05:19PM -0700, ann kok wrote:
Some DSL clients, some are working fine. (browsing...ping ...)
Some DSL clients have this problem they can't browse the sites. they can ssh the host but couldn't run the command in the shell prompt ping packet are working fine (no packet lost)
Why? but I still don't know why mtu can cause this problem
Path MTU discovery failures are one of the possible causes for what you're seeing. (For example, you can establish an ssh connection to a host, because none of the packets exceed the path MTU. But as soon as you run a command that generates a substantial amount of output, the connection will appear to hang because the remote host is repeatedly retrying to send the same data because it doesn't see an ack while the local host is never seeing the data because it exceeds the MTU). This is often caused by overly-aggressive filtering of ICMP. I recommend taking a look at http://www.znep.com/~marcs/mtu/ as well as http://www.cymru.com/Documents/icmp-messages.html and then checking the configurations of network devices to make sure that ICMP type 3 code 4 traffic isn't being blocked. ---Rsk