Jump to content
XPEnology Community

System unreachable after MTU change - HELP


rvmeush
 Share

Recommended Posts

I have been investigating very poor upload speeds on my HP Mediasmart EX490 running DSM 06.2.   I decided to try changing MTU settings to see if that would help.  In fact, when the MTU was increased beyond 1500 I noticed a very significant increase in upload speed.

 

I should have stopped there, but to see what would happen with a further increase, I changed the MTU setting to 9000.   After the system rebooted I can no longer access it on the network.  I have tried the web interface as well as an SSH client, but I get no response in either case.

 

Is there some way for me to edit the USB boot disk to set the MTU back to a lower value so I can access the server?

 

Thanks..

Link to comment
Share on other sites

After doing a search on "xpenology MTU 9000" I found that there were a number of other folks who had stumbled into the same problem I did.   I found a suggestion to manually edit the synoinfo.conf file on the hard disk.   I found the bad setting of 9000 for eth0 MTU and I changed it back to 1500.  After rebooting the system I was able to reconnect to the server.

 

I am still puzzled by the dramatic change in upload speeds that I observed.   With an MTU setting of 1500 the upload speeds I was seeing with Speedtest.py was about 10Mbits/sec.  When I changed the MTU setting to 2000 the upload speed jumped to almost 80Mbits/sec.

 

Can anyone tell me why this dramatic change would happen, and what technique I should use to optimize my MTU setting?

 

Thanks.

Link to comment
Share on other sites

  • 4 weeks later...

I won't get into technical details but your MTU should be set to a value where packets don't get fragmented. Above that value your speed will take a hit. As for the MTU 9000 issue crashing the system it is due a driver. This is a known issue since the first loaders Jun released (v1.0). I beleive I was the first one to have had the problem. At least I think I was the first one to have reported it and thanks to this I was able to make a tutorial on how to access the system partition to modify the value back to 1500 or whatever value you want.

 

You can check what your MTU should be here: https://forum.peplink.com/t/how-to-determine-the-optimal-mtu-and-mss-size/7895

Edited by Polanskiman
Minor edits.
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...