packet 1420 bytes greater than effective mtu 1398

[NIKHIL M K]

Hi All,

I'm getting "packet 1420 bytes greater than effective mtu 1398" PFA, when trying to send an SMTP traffic via IPSEC VPN, Could someone please advice on this?

Device: CISCO ASA 5525

[M02@rt37]

Hello @NIKHIL M K,

The error message you're seeing, "packet 1420 bytes greater than effective mtu 1398," indicates a Maximum Transmission Unit 'MTU' issue. It means that the packet you're trying to send is larger than the effective MTU of the network path, causing fragmentation or other problems.

You should review your IPsec VPN tunnel configuration to ensure that it can handle the expected packet size. Adjust the MTU settings within your VPN configuration as needed.

[NIKHIL M K]

Thank you, Could you please advise how to adjust the MTU for a specific VPN in ASA?

Thank you

Nik