tux99 Posted February 16, 2009 Report Share Posted February 16, 2009 (edited) I recently upgraded my home network to a Gigabit ethernet switch ( http://www.linuxtech.net/reviews/review_funkwerk_s208.html ), and would like to make use of the Jumbo frames, but I don't know much about it, especially I don't know if there are any drawbacks or negative side effects. I have added 'MTU=9000' in /etc/sysconfig/network-scripts/ifcfg-eth0 on all PCs that have a Gigabit ethernet card and are attached to the Gigabit switch (using CAT6 cables), everything still seems to work, and ifconfig is showing: UP BROADCAST RUNNING MULTICAST MTU:9000 Metric:1 What I wonder is, since not all devices on this switch are Gigabit, how does this affect traffic between a MTU=9000 PC and a device with a standard MTU=1500 setting? Will I get split up packets? Will this slow down traffic to the non Gigabit ethernet devices? Also my switch documentation says it supports Jumbo packets up to 8000, but it seems to work fine with a MTU=9000 setting on the attached PCs, why? I read somewhere that MTU=4000 is supposed to be better than MTU=9000 (it didn't say why), anyone know why? Any pointers to some related FAQ would be welcome too. Edited March 31, 2009 by tux99 Quote Link to comment Share on other sites More sharing options...
ianw1974 Posted February 16, 2009 Report Share Posted February 16, 2009 If the switch supports jumbo frames but fragments them for the 100/Full connections, then yes you'll have a performance problem with higher latency and lower performance. Have to check that the cards for 100/Full have support for jumbo frames or not. It needs to be enabled for all hardware so clients and servers rather than just enabling for the server only. Some info I found here: http://sd.wareonearth.com/~phil/jumbo.html Quote Link to comment Share on other sites More sharing options...
ianw1974 Posted February 16, 2009 Report Share Posted February 16, 2009 And here: but all Fast Ethernet switches and Fast Ethernet network interface cards support only standard-sized frames so no, you can't use it on 100/Full connections. Only gigabit. Source: http://en.wikipedia.org/wiki/Jumbo_frame Quote Link to comment Share on other sites More sharing options...
tux99 Posted February 16, 2009 Author Report Share Posted February 16, 2009 (edited) Thanks Ian, I did come across that Dykstra article before, but it's not written in a "language" that I completely understand... So how does "Path MTU discovery" come into play with this? I thought it would avoid fragmentation in case of different MTU? How can I check if I'm getting fragmentation? Edited February 16, 2009 by tux99 Quote Link to comment Share on other sites More sharing options...
ianw1974 Posted February 16, 2009 Report Share Posted February 16, 2009 This might help: http://7r09d0r.blogspot.com/2007/03/checki...g-on-linux.html at least in checking if jumbo frames are working OK. Maybe this also helps to see if you get fragmentation or not. I couldn't find anything else, but I'll add it here if I do. Quote Link to comment Share on other sites More sharing options...
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