I’ve been having an issue with copying data to my NAS for a while and I’ve finally had a chance to take a quick look at it. It’s an old NEtgear NAS Duo v1. I was only getting about 1/2 mb/s transfer to it, so I figured something was wrong there. I read a website from someone who had the same issue, their solution was to update the MTU for both the desktop and the NAS so I thought I would give it a try. OK so how do determine the optimal MTU setting for my desktop/nas?
Well that’s simple enough, you keep pinging a site with lower and lower packets until they stop being defragmented, add another number to it and bam, there you go.
Open Command Prompt
In the Command Prompt type in ping http://www..com -f -l 1472 and hit Enter. If you get ‘Packet needs to be fragmented but DF set.’ Message it means that the packet needs to be fragmented.
Drop the test packet size down (10 or 12 bytes) and test again until your reach a packet size that does not fragment.
Once you have a test packet that is not fragmented increase your packet size in small increments and retest until you find the largest possible packet that doesn’t fragment.
Take the maximum packet size from the ping test and add 28. You add 28 bytes because 20 bytes are reserved for the IP header and 8 bytes must be allocated for the ICMP Echo Request header. Remember: You must add 28 to your results from the ping test!
1440 Max packet size from Ping Test
+ 28 IP and ICMP headers
1468 Your optimum MTU Setting
In your case if the maximum packet size is 1452 the optimal MTU (Maximum Transmission Unit) is 1452+28 i.e. 1480. Here 1452 is the packet size of the data sent but the MTU is 1480.
To update your MTU on a windows machine, you can do this from the command line [I did it from a command line with administrative rights]
netsh interface ipv4 set subinterface “Local Area Connection” mtu=1458 store=persistent
There you go, sorted, updated the MTU on my NAS and now I’m getting 11/12mb/s which isn’t that much, but it’s an old NAS so I’ll forgive it.