How to get MTU setting changes via SSH or telnet to save and survive a reboot...

[Sean_90]

So I am using putty to update some Settings on my router and one of them was my mtu on some interfaces on the network. But when you reboot the settings revert back to defaults.

How can I get them to save? I have winscp is there a file via that program I can edit instead to update and save these settings? I think ifconfig file has the mtu settings in them but when I open the file its just all coding, symbols and unreadable.

 

[camieabz]

What's the router? Can't guess at commands otherwise. If you're getting into router command line, there should be a list of commands.

e.g. "copy running-config startup-config" (Cisco IOS) would take what's in RAM and save it to NVRAM.

 

[Sean_90]

Its running Asuswrt firmware.

Im pretty sure the command would be for example if I wanted to change the mtu to 1460 on interface eth0 i wuold use

ifconfig eth0 mtu 1460

It works I believe because then i type ifconfig and it shows all theinterfaces eth0, eth1, eth2 vlan1, vlan2 etc and shows the mtu. The one i changed shows the 1460 now instead of 1500 but if i reboot it erases back to 1500

What's the router? Can't guess at commands otherwise. If you're getting into router command line, there should be a list of commands.

e.g. "copy running-config startup-config" (Cisco IOS) would take what's in RAM and save it to NVRAM.

 

[camieabz]

Not familiar with that IOS, but taking a guess (so it's your kit; and it's your risk 😉 ), suggest you explore the NVRAM command. Guessing further, I've seen 'nvram commit' mentioned here and there. Assuming it even accepts that as a command, there's a chance that the router is set to reset on reboot, and ignore any non-factory changes.

If that's the case, you're looking at changing the cfg file, or using an NVRAM save / restore utility. I would tread very carefully if it were my router.

Out of interest, what's the need for 1460 MTU over the standard 1500? Are you getting fragmentation when you try the following:

ping [site] -f -l 1472