Linux Glider's server guide/ jumbo frames problem

Hi,

I've recently followed Glider's guide to setting up a basic linux server (which I have to say was fantastically written ).

I have a small issue however:

I have a 16 port Netgear gigabit switch that manages the traffic between all computers connected to the network. My mobo (A8N32-sli) has support for jumbo frames up to 9014 (IIRC) but the netgear ga311 NICs that I have installed in the other various computers (and the server) apparently is only capable of frames up to 7154.

If I use

Code:

sudo ifconfig eth0 mtu 7154

on the server, I lose connection between my computer and the server, yet with the mtu at 1500, it works fine.

How important is it that the frames are the same size? Is there a way of adjusting my onboard NIC in the Asus to 7154 (so that it matches the other cards) as I only have options of 1500, 4088, 9014 in the options.

EDIT: Even If I set the MTU to 4088 on the server and 4088 on my comp I still seem to have problems accessing files through Samba and I'm unable to establish a VNC connection (though putty seems to connect okay).

 

The MTU needs to be the same on both sides (or it will go haywire) and your switch needs to support jumbo frames.

Increasing the frame size will give you higher transfer speeds, and since you seem limited, 4088 is the best setting I guess, if your switch allows jumbo frames.

You can allways pop in a cheap gigabit card and set the framesize on that one.

 

I've read that setting MTU values in linux is different to setting it in windows. i.e. Linux will apparently list purely 'data' in the frame that is being transmitted as the MTU (e.g "1500"), whereas windows includes the additional bits that need to be sent with each packet (making it "1514").

So, 1514 in Windows equates to 1500 in Linux, 9014 equates to 9000...

Therefore, what does 4088 in windows equate to in Linux? 4074? A VNC connection still isn't possible with the server's MTU set to either 4088 or 4074, when the client is set to 4088.

EDIT: Also, it states on the box of the switch that it indeed supports jumbo frames, but I imagine that it may be capped at 7154, as per the NICs.

 

Hmm, never used Windows on jumbo frames... But MS logic says it isn't standard nor straightforward But by logic deduction, 4074 = 4088

It could be that VNC doesn't like the large packages.

And IIRC common switches with jumbo frame support go as high as 9k, but you need to enable that somewhere in the config most of the times. Probably a checkbox hidden somewhere in the switch config.

 

Cheers for the help Glider, much appreciated .

I don't think my switch actually has a config page of any kind, as it's a fairly straight forward unmanaged gigabit switch: http://www.overclockers.co.uk/showproduct.php?prodid=NW-048-NG&groupid=46&catid=115&subcat=

I wouldn't even know where to find it tbh, after all I edit my router settings by keying "http://192.168.xx.1" into a browser. But a switch doesn't have an ip as such. Or does it?

 

Managed switches do But if it's unmanaged then it'll probably enable it when needed I guess...

 

I guess the only way is to either get new NICs that can do the full '9014' Jumbo packets or use Netgear GA133s in every system and then use a program to determine the actual mtu they are using. Then apply the same mtu to the server with a 'sudo ifconfig eth0 mtu xxxx'.

To be honest though, it seems like too much aggravation/expense. I think I'll stick with 1500 for now and maybe look again in the future, maybe when there is an agreed standard for jumbo packets.

I wanted the server to be able to host all of our music and video files and then access them from any computer in the house.

A test with an mp3 streaming from the server to 4 PCs and 1 laptop in the house simultaneously was quite positive. Though a 1080p video only ran well on machines physically closer to the server. The furthest computer stuttered an awful lot. I thought that larger packets might help with this problem but, ah well.

Is there an app I can use on a Windows machine to test the transfer rate between itself and the Xubuntu server?

 

Wireshark (former ethereal) runs on Windows too