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10.3: MTU fixes for Ethernet and Airport connections
Authored by: nvdingo on Nov 24, '03 12:42:28PM

I remember setting my MTU to 1492 in my router years ago based on someone's suggestion. Never had a problem after that with PPPoE connections.

however, i can't remember WHY 1492 is the magic number.

Does anyone have a link to an explanation on this?



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10.3: MTU fixes for Ethernet and Airport connections
Authored by: sjoerd on Nov 24, '03 01:11:06PM
The normal maximum packet length is 1500. The PPPoE header occupies 6+2 bytes, leaving only 1492. Here are some links: http://www.allaboutjake.com/network/linksys/mtu.html

http://www.cisco.com/warp/public/794/router_mtu.html

http://www.qnx.com/developer/docs/momentics621_docs/neutrino/technotes/path_mtu.html

http://www.mynetwatchman.com/kb/adsl/pppoemtu.htm

This last one is interesting - it suggests that a setting of 1454 is better than 1492.

Sorry- I can't give you that last link correctly due to some *!@$#$ filter. Instead of *censored* type the following without the dot: t.wat

[robg adds: Hmm, hadn't noticed that Geeklog had "twat" in its censored list before. I've edited the link directly in the database; it should work when clicked now...sorry for the trouble!]

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10.3: MTU fixes for Ethernet and Airport connections
Authored by: Jean Boulanger on Nov 24, '03 07:06:09PM

Normally one could test for the max MTU possible, by pinging with large packet sizes and the 'do not fragment' flag set. However this seems to be impossible to do under recent OS X implementations, because the man page, and the usage for ping don't match the executable. For example, the man page says -D is the flag for 'do not fragment', but executable will not accept this flag.

Anybody know how to work around this?



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