ATS as forward proxy and ERR_PROXY_DENIED

[MAURIZI Lorenzo <l....@comune.jesi.an.it>]

Hi all,
I am using ATS 8.0.2 (from Debian 10 repos) as forward proxy for some servers that want to connect to the internet.
One of the servers (10.0.0.3) is trying to connect to some DellEMC servers on port 8443, but it can't.
Here is the error message of the application on the server:

Connectivity: Failed - The following destination host/port(s) are unreachable. Check your firewall ruleset and verify that port 8443 is open:
esrs3-core.emc.com:8443
esrs3-coredr.emc.com:8443

In the traffic_logcat I can find those rows:

1635926052.224 0 10.0.0.3 ERR_PROXY_DENIED/403 413 CONNECT esrs3-coredr.emc.com:8443/ - NONE/- text/html
1635926052.225 0 10.0.0.3 ERR_PROXY_DENIED/403 413 CONNECT esrs3-coredr.emc.com:8443/ - NONE/- text/html
1635926052.375 0 10.0.0.3 ERR_PROXY_DENIED/403 413 CONNECT esrs3-core.emc.com:8443/ - NONE/- text/html
1635926052.376 0 10.0.0.3 ERR_PROXY_DENIED/403 413 CONNECT esrs3-core.emc.com:8443/ - NONE/- text/html

I have checked that the proxy server itself is able to connect to the port 8443 of those DellEMC servers:

root@proxy:/etc/trafficserver# telnet esrs3-core.emc.com 8443
Trying 128.221.236.246...
Connected to esrs3-coregtm.emc.com.
Escape character is '^]'.

root@proxy:/etc/trafficserver# telnet esrs3-coredr.emc.com 8443
Trying 168.159.224.236...
Connected to esrs3-coredr.emc.com.
Escape character is '^]'.

As the connection is in https and the certs are untrusted, i put the certificate verification off in records.config:

CONFIG proxy.config.ssl.client.verify.server INT 0

But to no avail.

Can you help me to solve this problem?

Thanks in advance.

_______________________________________
Lorenzo Maurizi
Servizio Sviluppo Tecnologico
Comune di Jesi
0731 538226