Re: [exim] GMail and TCP Fast Open

On Tue, Dec 07, 2021 at 10:22:37PM +0000, Andrew Hearn via Exim-users wrote:
> We have a direct interconnect to Google, so there is only a fibre
> between our router and Google's router, that part of path is stable and
> identical - though there are a number of hops withing Google's AS that
> could be changing.
>
> ping/mtr - no packet loss

Expected in case of broken PMTUD, and in this case mtr is helpful for
monitoring path, not loss value (wich may be zero).

> Tried reducing MTU (can't pmtu discover to gmail as they block too much
> ICMP) - no difference
>
> Checked IPv4 vs IPv6 - no difference

You were suggested to record traffic dump. Look for disconnections and
extract regions from 2-3 last server's ACKs to client's RST.
--
Eugene Berdnikov