So tonight I decided to completely dig through, test, research, and understand the miracle that is Gigabit Jumbo Frames. What are jumbo frames? Reader's Digest version: standard Ethernet frames are 1500 bytes each, which means for every 1mb of data you send/receive, your Ethernet adapter is building and sending about 700 "frames" holding the data. Jumbo frames lessen the load on your adapter by allowing bigger "frames" to be used, meaning less overhead and... yes... faster Ethernet performance. It has absolutely no effect whatsoever on Internet browsing. Just LAN transfers, like copying a Blu-Ray movie from one computer to another. GbE is already damn fast even with 1500-byte frames, but sometimes - like on my Atom media center - the CPU just gets swamped trying to keep up with "line speed" and it ends up getting capped due to the CPU load. That's where jumbo frames help. On with the guide. This is just a run-down of what jumbo frames need to work, and how to test it. REQUIREMENTS ALL of your equipment - switches, and all devices on the network - must be Gigabit, and must support Jumbo Frames. No exceptions, unless you just don't want to be able to use those devices. That includes your router.* An Ethernet adapter that supports jumbo frames. Yes, there are many that don't. An Ethernet driver that also supports jumbo frames. Your adapter might, but your driver might not. Bad manufacturer. Bad. And to reiterate, your switch must also support jumbo frames. I just found out that mine, a D-Link DGS-1005D, which I've owned since 2005-ish... doesn't. Some sites claim it does, but I just tested it, between my Netgear GS605 v3, and the D-Link, and jumbo frames time out ONLY on the D-Link. Ah well. "GOTCHAS" If a single part of your network doesn't support jumbo frames, you can enable it all you want, but all you'll get are mysterious network time-outs and issues. This can be extremely frustrating to troubleshoot when your internet access works fine - I'm guessing that's because the router informs the switch or PC that it only supports a smaller MTU, or because all the data in each frame is only 1500 bytes anyway. So you can get online fine, and you can PING your other computer (32 bytes!)... but you can't communicate with it. Jumbo frames. TESTING If you've enabled Jumbo Frames on all your connected PCs, and all the above requirements are met, use this to test if jumbo frames are working: Code: ping 192.168.0.2 -f -l 6099 ... where "192.168.0.2" is, duh, the computer you want to test. The switch "-f" sets TCP/IP "DF", or "Don't Fragment", so the adapter/driver/switch doesn't break it up to allow it to pass without jumbo frames. The switch "-l 6099" specifies the size of the ping data - 6099 bytes is good to test a 6k MTU (6130 bytes), since there also needs to be room for the TCP/IP data in the frame (a few bytes of overhead - yes, per frame. Aren't you glad you're doing jumbo frames now?). If the packet isn't getting there in one piece, it'll time out. If it DOES respond, that means jumbo packets are working, at least for 6kb. 9kb MTU is the general accepted norm, but I'm sitting next to a computer right now (my quad desktop) that, despite setting 9kb, only shows a MTU of 6kb in netsh. "netsh"? Ah yes, that's the other test. Code: netsh int ip show interface (may actually be "interfaces" depending on your OS) That will show you what Windows is actually using for your current adapter MTU. If it's still 1500, something's up. Many drivers misbehave in this regard, since jumbo frames is such a delicate system, manufacturers don't expect "consumer devices" to be using it. So they slack on the support of it. It's kind of a catch-22... poor support = unreliability = nobody uses it = poor support. Such is the world of computers. So this should solve a few mysteries of jumbo frames... it's a fun little thing but you've got to make sure it actually works with your equipment * - Well, I may not be 100% correct on this. My router that I'm posting this through is a basic 100mbps Netgear dealie, and it seems to be working OK. I'm just concerned that my computer will try to send it a larger packet, and stumble over it. I tried sending a fragmented ping, but it doesn't reply. So IDK... edit: I really wish SJ would fix the site CSS so font definitions worked right... /sigh
If I had the right equipment I'd definitely be playing around with this (I have plenty of Blurays to transfer, just dont feel like forking out the cash right now for the equipment). Although this concept isn't too complicated it feels good to know that all the time spent at school and studying is worth it, as I understood every aspect of your post. A year ago, I would have read this post and said "Huh?" and then exited the thread. Got my A+ cert and am working on my Network+. I recently got transferred to the IT dept at my office. I'm gettin' there.
I liked it, +rep, not to many people talk about TCP/IP and you did. I liked that. Not to many people understand that I have a feeling. EDIT: It won't let me add to your rep. Ill add when I can.