How to specify IP Address Range with CIDR suffix

If you configure firewall rules, then you need to allow/block a range of IP addresses.

One way to specify a range of IP address is to use IP address / CIDR suffix (e.g.

The CIDR suffix can be confusing.  So here is a quick reference table:

CIDR Effective IP Range Total addresses to 16,777,216 69.208,0.0 to 65,536 to 256 1

Technical Reference:


How to Setup AWS Multi-Factor Authentication

If you manage AWS servers, enabling multi-factor authentication (MFA) can increase your security quite a bit. 

You can choose a virtual MFA device (i.e. mobile app on a Phone) or a hardware MFA device.

For virtual MFA device, you can install Google Authenticator on your Android phone.

During the setup, it is critical that you copy and save the AWS’s Secret Configuration Key to a secure place.  Once the setup is complete, you won’t see it.

If you lose your phone, you can install Google Authenticator on a replacement phone.  Otherwise, you are locked out of your account.

Unless you are are a great typist, I would recommend you install ZXing’s BarCode Scanner, as suggested by Google Authenticator.

By the way, you can rename the account name on Google Authenticator to something that is easy for you to relate.

By the way, you can also get a cheap Android phone, install Google Authenticator and set up using the Secret Configuration Key and stores it in a safe.  It is like a spare key.  If you ever lose your original phone, you can use this backup phone to provide the token.