I started doing some testing of my home network, to see which devices are Jumbo Frame compatible, and eventually if I could gain anything from enabling it.
As the figure shows most of the devices in my network are using WLAN. Only the router, firewall and wireless access point are actually connected with CAT 5 cables. Even the Windows 2003 server is communicating with an external USB Linksys WLAN adapter.
One very significant fact when discussing Jumbo Frames is that it is ONLY available on 1Gb network devices. 100Mb/10Mb devices do not have Jumbo Frame capability. And since my network is mostly WLAN this is a shop-stopper. However, I still wanted to figure out what it would take to JF-enable LAN, and also to gather some information about the network.
The most obvious thing was to check the network drivers on the various machines. On my IBM T42 the Intel PRO/Wireless 2200BG card unfortunately doesn't support Jumbo Frames (JF), but the Intel PRO/1000 MT Mobile infact does. The gigabit NIC seems to support 4KB, 9KB and 16KB packets.
By pinging the access point I was able to determine that my T42 WLAN card has packetsizes of 1272 bytes. The size was determined by pinging with the command 'ping -f -l 1272 172.28.5.3', and adjusting the packetsize until the NIC returned error "Packet needs to be fragmented but DF set.". Both on Julies Dell Inspiron 6400 laptop's WLAN card and on the USB Linksys Wireless-G adapter the packetsize is 1474bytes.
The Dell laptop's LAN NIC is only 10/100Mb, so it doesn't have JF support.
On the Dell server the LAN NIC is an Intel PRO/1000 MT card (not unlike on the T42), but Jumbo Frames is not available in the driver settings. Perhaps it only requires a driver update.
My switch, a D-Link DES-1008D, is a mere 10/100 Fast Ethernet switch - so it does not support JF either.
So it seems like my network is far from Jumbo-Frames-ready. Ok, so now at least I know. No point in enabling JF on my laptop yet then.
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