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Why do Mac OS® and Windows® 98 connections freeze when running PPPoE on the gateway?

April 26, 2017freeze Gateway Mac PPPoE running

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Why do Mac OS® and Windows® 98 connections freeze when running PPPoE on the gateway?

2 Answers

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Thanks to Michael Wozniak for figuring this out and Dan Flemming for the Mac solution: This is due to what is called a “Black Hole” router. Mac OS and Windows 98 (and maybe other Microsoft OSs) send TCP packets with a requested segment size too big to fit into a PPPoE frame (MTU is 1500 by default for Ethernet) and have the “do not fragment” bit set (default of TCP) and the Telco router is not sending ICMP “must fragment” back to the www site you are trying to load. (Alternatively, the router is sending the ICMP packet correctly, but the firewall at the www site is dropping it.) When the www server is sending you frames that do not fit into the PPPoE pipe the Telco router drops them on the floor and your page does not load (some pages/graphics do as they are smaller than a MSS.) This seems to be the default of most Telco PPPoE configurations (if only they knew how to program a router… sigh…) One fix is to use regedit on your 95/98 boxes to

0

Posted

Thanks to Michael Wozniak for figuring this out and Dan Flemming for the Mac solution: This is due to what is called a “Black Hole” router. Mac OS and Windows 98 (and maybe other Microsoft OSs) send TCP packets with a requested segment size too big to fit into a PPPoE frame (MTU is 1500 by default for Ethernet) and have the “do not fragment” bit set (default of TCP) and the Telco router is not sending ICMP “must fragment” back to the WWW site you are trying to load. (Alternatively, the router is sending the ICMP packet correctly, but the firewall at the WWW site is dropping it.) When the www server is sending you frames that do not fit into the PPPoE pipe the Telco router drops them on the floor and your page does not load (some pages/graphics do as they are smaller than a MSS.) This seems to be the default of most Telco PPPoE configurations.