How is the tcp set in openSUSE?

By that I mean to ask what value is set for the mtu and for the the receive window by default.

Back when I was running suse 10.1, I used to set the MTU to 1488 (or whatever is the recommended for PPPoE over DSL). The normal default is 1500.

I’m not sure whether I did that manually with the “ifconfig” command, but I probably set the system configuration for the interface.

Right now, I am running factory (basically pretesting 13.2 before release). If I use

Yast → Network Devices → Network Settings

and click on the interface name (which is no longer “eth0” for me), then there is a setting for MTU under the “General” tab.

If you are using NetworkManager, there is probably a setting there for each connection under the IPv4 settings while editing the connection details. I’m not currently running NetworkManager, so I cannot check the details.

As for window size – I have never had a need to set that with linux.

Ok, I know about those settings in Yast but the mtu setting is blank unless it’s manually set so I didn’t know what the default was. I’m not sure about the performance comparison if I fool with that or set the receive window using sysctl.conf but it does seem like I can improve it. The problem is that I think there is a command to check the window size using the terminal that I don’t I don’t remember right now but it doesn’t change what it reports after I put in my own settings.

That’s why I’m asking.


The default MTU is 1500. You can check the output of “/sbin/ifconfig -a” to see your MTU.

I’m not sure about window sizes. I think the driver for the card sets the defaults.

TCP Window sizes are set in the OS because is a Layer 3 configuration, is not a network card issue.

I discuss how to set it, and other similar TCP/IP settings in my still relevant article on “Optimizing TCP/IP”


Me read that.

With each setting described, there should also be a command which reads and verifies the new setting in the system.
If anything doesn’t work as expected, post the exact details (preferably in CODE blocks) what you’re seeing.

Note also that things like window sizes and how those windows are used can also be set and perhaps over-ride other settings by your choice of TCP/IP Congestion Control Algorithm.