Apr 11, 2016

Enabling jumbo frames on Cisco ASA (MTU size higher than 1500)

If you want to increase the MTU size for a specific interface (enable support for jumbo frames), you need to implement the changes described bellow, but first you should check the supported models and prerequisites on Cisco ASA Configuration Guide. Note that a reboot is required

Jumbo frames should be enabled to receive packets more than 1500 MTU (this command will take effect after the running-config is saved and the system has been rebooted):
jumbo-frame reservation

TCP MSS needs to be adjusted to pass large TCP segments:
sysopt connection tcpmss bytes

Set MTU size:
mtu interface_name bytes