Score:-1

What is a netmask and how is it relevant to IP whitelisting?

id flag

https://dnsmadeeasy.com/support/subnet

I was told to whitelist an IP 124.133.44.42 (not real ip), but I am wondering what I should enter as a netmask to whitelist the IP by default. I am guessing any user within the sub network should be whitelisted. So should I use a netmask of 255.255.255.0 to cover every user?

John Mahowald avatar
cn flag
Please do not make up example IP addresses assigned to someone else. Use the real IP address, or RFC 5737 test nets, such as 203.0.113.42.
Score:1
za flag

No, no, no. Whitelist only the the precise IP. Sibling IPs can be used by completely different people and you don't want to whitelist them too.

"The address" netmask is all ones, /32 in CIDR notation or 255.255.255.255 in bitmask terms.

When you are asked to permit something, never think of "what else I could permit". Work it out in the opposite way: what exactly you need so I could permit the least, the very minimum? Maybe I don't need to "whitelist an IP", but only ensure it will always be able to access the tcp port 80 on my machine?

The 255.255.255.0 a.k.a. /24 netmask you thought about is completely arbitrary and doesn't correspond to any term in the real life. (It probably could mean something in the past when Internet was classful, but not today. And, since we don't know which IP you were told, we can't determine which address class it belongs anyway. And even if we could, that still was unneccessary.)

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