[Cryptography] Two quick questions about IPsec AH

[Paul Wouters]

On Thu, 6 Jan 2022, Phillip Hallam-Baker wrote:

> I am not sure whether AH is being used, but I rather suspect that it is not because of some other design decisions in IPSEC.
> 
> IPSEC as specified in the RFCs was simply unusable because it didn't work through NAT. The IPSEC authentication included the source
> address and that caused connections to fail through NAT boxes.

Indeed. In RFC 8221 I included:

    [ESP] ENCR_NULL status was set to MUST in [RFC7321] and remains a MUST to
    enable the use of ESP with only authentication, which is preferred
    over AH due to NAT traversal. ENCR_NULL is expected to remain MUST
    by protocol requirements.

Personally, I would have preferred to kill AH outright, but some people
did complain that it would affect them. So, it is indeed used at very
few places, deep down in the Moria of networks where no NAT dares to go.

Thanks for all the IPsec history emails.

Paul