In security group, every inbound port I add, two rules are added, one for 0.0.0.0/0, the other ::/0. What do they each mean?
5 Answers
0.0.0.0 means that any IP either from a local system or from anywhere on the internet can access.
It is everything else other than what is already specified in routing table.
When we add /0 is for the IPv4 whereas ::/0 is for IPv6 is known as CIDR
Coming back to your AWS part, when you define 0.0.0.0/0 or ::/0 that means all the IPv4 and IPv6 ranges respectively can access your AWS service(s).
Ranges for IPv4 is from 0.0.0.0 to 255.255.255.255 where as IPv6 have 2^128 addresses.
An IP address is built by 32 bits, the slash tells you how many bits are used to identify the network section, the rest of the bits are used for the host. For example, 255.0.0.0/8 tells you 8 bits are for the network and 24 are for the host, so you migth have 16777214 possible IPs comming from that 255 network.
In case of the notation 0.0.0.0/0, it means you dont use any identifier for the network, therefore you have the whole 32 bits for the IP, meanining ALL possible IPs, which means all requests are allowed.
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