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jumbo frames
Authored by: cynikal on Jun 22, '06 04:12:40PM

i've read that some of the macbooks and possibly other gigabit enabled macs support jumbo frames (ethernet frames up to 9000 or so bytes each, vs the default 1500 bytes).

has anyone tried setting these up ? my powerbook has the option grayed out in the tab, and this cisco 4507 gig blade i'm connected to says it doesn't support setting the mtu:

a4507switch(config-if)#mtu ?
<1500-9198> MTU size in bytes

a4507switch(config-if)#mtu 9198
% Interface GigabitEthernet7/5 does not support user settable mtu.



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jumbo frames
Authored by: hieronymus bozo on Jun 22, '06 06:41:19PM

indeed, my macbook 13 2.0ghz does support jumbo frames.

for kicks, i checked a few other machines (all running tiger or tiger server except the xserve g4, which is 10.3.9 server, fwiw) and here's what i saw:

xserve g4 solo 1.8ghz: YES, supports jumbo frames
mac mini g4 solo 1.8ghz: NO, does not
xserve g5 dual 2.5ghz: YES, supports jumbo frames
powermac g5 dual 2.0ghz: NO, does not
powermac g5 dual 2.7ghz NO, does not
powermac g5 quad 2.5ghz YES, supports jumbo frames

what are the implications of enabling jumbo frames? which switches/routers will break? which will thrive, if any, and what will the speed boost be? why does a crappy moon-era g4 xserve support them, yet the newer, technically identical mini ;-) and the second from last g5 released does not?

this functionality would be a good addition to the Mactracker app. i'll see if i suggest getting it added. in the meantime, perhaps others can post additional machines.



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jumbo frames
Authored by: cynikal on Jun 27, '06 05:27:16PM

jumbo frames if you were curious, let you send larger amount of data before having to break that stream of data up because the underlying media can only send frames of a certain size.. normally ethernet has a maximum frame size of 1500 bytes, jumbo frames let you get frames up to 9000 bytes in size, thereby decreasing the overhead of having to re-pack the next amount of data in a new packet (inserting into new headers at one end, decoding those headers at the other end). When it comes to higher speed networks, such as gigabit ethernet, this might help squeeze some more performance out. Of course the switch you're connecting to has to support gigabit and jumbo frames (and in theory, it's uplink should also do the same and so on and so forth).

What i'm curious about is, what kinda performance improvement has anyone seen using jumbo frames?



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