CCNA Basics: Introduction to Wildcard Mask
Author : Amandeep Kaur
Today we are going to talk about the Wildcard Mask which generally we are using while configuring OSPF. Wild Card Mask is an important concept and everybody should aware of this concept
Sometimes people ask if there is subnet Mask when why we required Wild Card Mask, even i was not aware why it is necessary to use Wild Card mask but let's talk about wild card mask in detail to understand.What is a wild card mask?
Wild card masks are used for a variety of different tasks. OSPF area definitions and some access lists use them to define a certain part of the network. They work much like subnet masks but in reverse. Let's talk about one of the example in the Subnet C class as below:
So what you guys think about the wildcard Mask. The wild card mask is essentially the reverse of the subnet mask. So if the binary subnet mask looked like
Wild card masks are used for a variety of different tasks. OSPF area definitions and some access lists use them to define a certain part of the network. They work much like subnet masks but in reverse. Let's talk about one of the example in the Subnet C class as below:
- IP address with Subnet Mask : 202.1.192.0/22
- Network – 202.1.192.0
- Subnet mask – 255.255.252.0
- Wild Card Mask – 0.0.3.255
Explain in details below
- Subnet Mask : 11111111.11111111.11111111.00000000
- Wild card mask would look like this: 00000000.00000000.00000000.11111111
- 192.168.127.1 /27
- Network – 192.168.127.1
- Subnet mask – 255.255.255.224
- Wild Card Mask – 0.0.0.31
The wild card mask would look like this: 00000000.00000000.00000000.00011111
Now that’s a little more confusing isn’t it? What might even be harder to understand is if you were simply given this.
Then to convert a mask from standard notation to wild card you simply subtract the subnet mask from 255.255.255.255.
- access-list 1 permit 192.168.127.1 0.0.0.31
- 255.255.255.255 – 0.0.0.31= 255.255.255.224
- 255.255.255.255 - 255.255.255.224 =0.0.0.31