topic Re: Subnetting question for a wildcard that covers a bunch of slash 25s in General Topics

Subnetting question for a wildcard that covers a bunch of slash 25s

KennaJosh — Mon, 01 Apr 2024 16:14:10 GMT

Hi guys,

I work for a retail company. We have a bunch of subnets in our different stores where the 3rd octect is a different odd number. Like so -

10.218.1.0/25
10.218.3.0/25
10.218.5.0/25
...
10.219.253.0/25

I'm creating a security rule that will allow all these subnets to talk to a vendor. I'd rather not create an address for all these slash 25s, so I'm trying to figure out a wildcard mask I can use that covers all the networks I need. One guy told me to use 10.218.1.128/0.15.254.127 and another guy said 10.218.1.0/0.0.0.127 would work. I don't know much about subnetting but it doesn't seem like either of these are working in our firewalls. Anyone got any ideas?

Cheers

Re: Subnetting question for a wildcard that covers a bunch of slash 25s

Claw4609 — Mon, 01 Apr 2024 18:53:40 GMT

Hello,

So to clarify you want an object containing all of 10.218.0.0-10.218.255.255? If so you could do a few different things:

IP Netmask (correction from the image, it would be /16):

IP Range:

Wildcard (correction from the image, it would be 0.0.255.255):

Re: Subnetting question for a wildcard that covers a bunch of slash 25s

rmfalconer — Mon, 01 Apr 2024 19:01:25 GMT

Without writing it out in binary, I think 10.218.1.0 / 0.0.254.255 should cover it.

First 2 octets must match.

For an address to be odd, there needs to be a match in the final bit, meaning 0 in that spot in a wildcard mask. (Every other bit is a power of 2, so adding 1 to any other combination will make it odd)

Last octet doesn't have to match anything, so any host is permitted.