(Message mtu:16) Date: 02 Dec 1997 20:22:02 MST From: "Gary Palmer" Newsgroups: comp.dcom.sys.cisco Subject: Re: Cannot reach sites with MTU<1500 Approved: news@news.colorado.edu X-Return-Path: dhesi@rahul.net X-Nojunk-Status: OK 0 Organization: University of Colorado at Boulder Sender: daemon@lace.colorado.edu Distribution: world Nntp-Posting-Host: lace.colorado.edu In-Reply-To: Your message of "Mon, 01 Dec 1997 14:55:28 +1200." X-Note1: message-id generated by recnews X-Note2: mail msgid was <26617.881108211@orion.webspan.net> Xref: samba.rahul.net comp.dcom.sys.cisco:41133 Franck Martin wrote in message ID : > I had this strange problem with a very few sites on the net: > > www.hotmail.com > www.compaq.com > www.ausaid.gov.au > > The connection to my ISP is very slow 9600bps, therefore at these speeds > it is better to put an MTU of 576 for better usage, I set it up on my > CISCO 2500 on the serial port. Unfortunately, I was not able to browse > these particular sites, but I had no problem with 99.9% of the INTERNET > web sites. > > I set the MTU to 1500 and everything went fine. Please note that I did > it at the same time as my ISP did it. > > I wrote to the webmaster of these sites, and so far only one answered me > letting me know that they use a cisco local redirector. > > It seems that these few sites set the don't fragment flag in their > packets, which is highly strange, or is it the cisco local redirector > which has got this behavior? > > If anyone can bring the light on this issue. The sites are filtering inbound ICMP, and probably running with Path MTU discovery. When you run with a MTU less than their LAN's MTU, you lose, as they don't find out that they need to fragment their packets. I think some WWW sites at sun.com have the same problem. Gary