Which ports are opened by default in the same security group to communicate with instances within it-CodePudding

Are all ports within the same security group opened by default or should we specify them? Like for example TCP on ports 0-65535 and ICMP IPv4 on all ports?

I ask because I noticed I don't need to specify SSH port 22 within the same security group to be able to access other instances in the same security group, so I wonder if this applied to all protocols and all ports.

This is how it currently looks like. The instances within the SG have an IP in the range 172.31.80.0/20. I only allowed SSH from other security groups, not within it.

CodePudding user response：

By default, instances within the same security group can't talk to each other (over any port); there is an exception however for the default security group.

From the documentation:

Instances associated with a security group can't talk to each other unless you add rules allowing the traffic (exception: the default security group has these rules by default).