We are seeing the same, but seems like it's mostly affecting delivery for broadcom.com, and a few other smaller domains. However, connectivity to the MX listed by gmail.com (and most other domains using GSuite, etc) are working fine over IPv6. You may also want to ask the mailop list. -- Alex Brotman Sr. Engineer, Anti-Abuse & Messaging Policy Comcast

-----Original Message----- From: NANOG <nanog-bounces+alex_brotman=comcast.com@nanog.org> On Behalf Of Marco Davids (Private) via NANOG Sent: Tuesday, February 27, 2024 8:03 AM To: nanog@nanog.org Subject: IPv6 connectivity to mx[1-4].smtp.goog.

Hi,

At https://urldefense.com/v3/__https://internet.nl__;!!CQl3mcHX2A!Dc9AZo4F nrpVmuo3Ehg5iQUAd4uTAsCdz9MWYKJqFWyWK7_XnaDnWN3_DkOAVq2e5 CXVOb2triASeebvdg$ we're seeing IPv6 connection issues on TCP port 25 (SMTP) to mx[1-4].smtp.goog.

Either 100% DROP (so no TCP connection) or ⅔ failure to setup connection.

Further testing seems to confirm the problem is bigger and on Google's side.

So, this fails:

echo 'quit' | nc -6 -w 3 mx1.smtp.goog. 25

and this works:

echo 'quit' | nc -4 -w 3 mx1.smtp.goog. 25

(on MacOS use -G instead of -w)

Is anyone else seeing this? Any idea what is causing this?

-- Marco