IPSec with AES-256-GCM key length

[mstoebich]

So we are in the process of setting up a VPN to a customer. Their requirement is ipsec with AES-256-GCM and a key length of 256. If i look at my options inside the VPN/ipsec tab, I can't find a key length of 256 bits, the dropdown only shows 128-,96- and 64-bit key lengths when using AES-256-GCM.
After some googeling this gets even more confusing. Doesn't the 256 in AES-256-GCM tell the key length? But then why can i even change it on my pfsense? and why only to these three lower values?

Also: maybe this isn't the keylength, but the block size?

I can't wrap my head around that.

[jimp]

AES-256-GCM is a 256-bit key length. The other selector there, in the case of AES-GCM, is the ICV, not a key length.

[mstoebich]

Thanks for the answer, I've figured that out a few days ago and totally forgot to mention it here (shame on me)...

So this dropdown doesn't always 'behave' the same way?

[jimp]

AES-GCM is the only exception to the way the drop-down works.