When Oracle Cloud's Ubuntu instance doesn't accept connections to ports other than 22

Thanks to the free trial periods, I’m testing this and that on Oracle Clouds.

While running a Ubuntu instance, I was stuck with a weird problem that made me pull out hairs for hours.

My problem was this:

I added several ingress rules in my default security list,

but the instance didn’t accept any connection to ports other than 22, the SSH port.

2020-01-15_20 44 58

I looked into nearly every network setting in the Oracle Cloud console and searched for similar problems on the web,

but nothing worked.

After some time and more tests, I began to suspect that a firewall or something was blocking connections.

When SSH server on port 22 was down, it said connection was refused.

But when I tried connecting to other ports, it said no route to host.

Hmmmm… interesting, something was blocking connections.

I searched for any configuration for iptables.

There were two files in /etc/iptables/, and gotcha!

I found rules that were rejecting connections in /etc/iptables/rules.v4 file:

# CLOUD_IMG: This file was created/modified by the Cloud Image build process
# iptables configuration for Oracle Cloud Infrastructure

# See the Oracle-Provided Images section in the Oracle Cloud Infrastructure
# documentation for security impact of modifying or removing these rule

:OUTPUT ACCEPT [463:49013]
:InstanceServices - [0:0]
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p udp --sport 123 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited

Because of these things, changes in the console would never have effects.

Amazon AWS’s Ubuntu images don’t have such configurations by default, so it maybe due to Oracle’s security policy.

I didn’t want to take Oracle’s default security policy down, so I just added following lines:

-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT

# my custom rules
-A INPUT -p tcp -m state --state NEW -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 443 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 3000 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 8080 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 8888 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22022 -j ACCEPT
-A INPUT -p udp -m state --state NEW -m udp --dport 60000:60100 -j ACCEPT

-A INPUT -j REJECT --reject-with icmp-host-prohibited

By both adding ingress rules on the console and inserting lines in /etc/iptables/rules.v4,

I could finally connect through other ports without any problem!

Oracle is a relatively new runner in the cloud race.

It needs some more work on it, but I think the new Always Free service is a really attractive starter for developers like me.