Modification of the interface MTU

Question

Hi all! 
 Quick question regarding XGS 126: MTU is a property of the physical interface. If I want to reduce the MTU for a VLAN I have to do it on the physical interface. 
 By adjusting MTU value I seem to lose the VLAN interface and the associated dependencies e.g. firewall rules. 
 Is there a way to prevent this? 
 Thank you for your input! nk

Vivek Jagad · Answer

Hello Nils Kroll , Thank you for reaching out to the community, you can leave the MTU settings default and change the mss size according to your requirement ! https://docs.sophos.com/nsg/sophos-firewall/19.5/Help/en-us/webhelp/onlinehelp/CommandLineHelp/DeviceConsole/Set/index.html#network e.g: console> set network mtu-mss Port2 mtu default mss <number value>

Nils Kroll · Answer

Hi! 
 This is a short-term workaround (MSS config). Previously we used UTM instead of XG with reduced MTU but we missed that detail when switching to XGS. The goal is therefore a reduced MTU again. 
 I had hoped that there is a way to correct the MTU without serious effects.. I will reduce the MTU in any case and restore the lost configuration. 
 Thanks for your support!