In networking MTU stands for Maximum Transmission Unit and dictates the maximum size for any packet of data that is sent from a device over a network. MTU is measured in bytes and has a maximum value of 1500, so an MTU of 1500 dictates that the largest packet of data that can be sent in one go from a device over a network is 1500 bytes.
MTU setting on IPSEC Tunnel - Cisco Community I just finish setting a gre tunnel with IPSEC and 3DES encryption. When I used the default settings, configured by the SDM, it set the tunnel MTU to 1420. With that default setting I was able to bring up the tunnel, but simple tcp services would not work, like viewing a HTTP server of using FTP. So The default MTU sizes for different network topologies Apr 17, 2018
During the negotiation, a maximum MTU size is negotiated. Since the PC negotiates and its default MTU size is 1500 bytes (Windows 3x, 9x, NT, ME, and so forth), the web server negotiates an MTU size of 1500 bytes. Therefore, regardless of the MTU size you configure on the router, the web server still sends packets up to 1500 bytes in size.
TCP/IP performance tuning for Azure VMs | Microsoft Docs The maximum transmission unit (MTU) is the largest size frame (packet), specified in bytes, that can be sent over a network interface. The MTU is a configurable setting. The default MTU used on Azure VMs, and the default setting on most network devices globally, is 1,500 bytes.
During the negotiation, a maximum MTU size is negotiated. Since the PC negotiates and its default MTU size is 1500 bytes (Windows 3x, 9x, NT, ME, and so forth), the web server negotiates an MTU size of 1500 bytes. Therefore, regardless of the MTU size you configure on the router, the web server still sends packets up to 1500 bytes in size.
Manually Managing MTU Size in Mac OS X | MacGuruPro