ip tcp adjust-mss on FTD with FMC

[ben.levin1]

Hi all,

I'm working on setting up an IKEv2/IPSec VPN tunnel from an FTD (6.2) managed by FMC to Azure.  The tunnel is up and icmp is working fine but our server engineer is reporting issues with RDP and domain controller replication.

We're wondering if MTU or MSS could be causing these issues.  The FTD interface MTU are currently default (1500) but I don't see a way to set ip tcp-adjust mss on the FTD. I'm not sure if there's a way to do this in FMC or via the FTD command line.

Thanks.

[Marvin Rhoads]

You can adjust it with FMC using a Flexconfig object.

https://www.cisco.com/c/en/us/td/docs/security/firepower/623/configuration/guide/fpmc-config-guide-v623/interfaces_for_firepower_threat_defense.html#ID-2076-00000035

[williaat0125]

Great link. I learned that you can disable the TCP MSS value from this link. Cisco didn't show how to do this. I'm assuming that simply setting this value to 0 disables this setting. Honestly, we prefer to allow our endpoints to use their MSS setting and not have the FTD involved.

Any thoughts?

[MHM Cisco World]

If you have issue make new post it is better 

MHM