Fortigate 70D - IPSEC VPN to AWS VPC - MTU Size Configuration?

[hamlin11]

When setting up an Amazon VPC VPN connection, when one clicks "download configuration" and selects Fortigate 4.0, the following is provided within the configuration file. 

However, when this is executed in the Fortigate 70D CLI, the following error occurs: 

> command parse error before 'mtu'

> Command fail. return code -61

Is there a way to set the MTU value on a Fortigate 70D running 5.2.x? 

config system interface   edit "vf00894a8-0-p1"    set vdom "root"    set ip 169.254.10.134 255.255.255.255    set allowaccess ping    set type tunnel    set tcp-mss 1387    set remote-ip 169.254.10.133      set mtu 1427    set interface "wan1"  next end

[hamlin11]

The answer is as follows:

[ul]

You must set mtu-override enable on the interface in order to set the MTU size.

HOWEVER, mtu override is not available on IPSEC Tunnel interfaces, which is my underlying problem here. [/ul]

From the CLI Reference for 5.2.6:

> (mtu-override) Select enable to use custom MTU size instead of default (1500). This is available only for physical interfaces and some tunnel interfaces (not IPsec). Some models support MTU sizes larger than the standard 1500 bytes.

It is a bit strange, perhaps, that Amazon's downloadable config for Fortigates contains an MTU override. Perhaps this was available in the 4.0 operating system which the Amazon config is based upon. I also wonder if this has something to do with the ASICs which I believe are used to process some or all IPSEC VPN traffic on some models, including the 70D.