Learning by Doing: CISCO Certified Network ... - SCN Research

Therefore, when we convert this wildcard mask back to decimal we get a wildcard
mask of 0.0.0.31 for our subnet wildcard mask.
3. Finally, unlike subnet masks, wildcard masks do not have to be contiguous (all
zeros in a row)…we can mask out certain ips. Write a wildcard mask for a the
odd numbered ips in the entire subnet containing the ip address of 172.16.2.34/27
Let’s convert the ip address to binary:
10101100.00010000.00000010.00100010
Then let’s figure out the network, subnet, and host portions:
10101100.00010000.00000010.00100010
network.network.network.subnet host
Since they want an exact match for all network plus subnet bits then the wildcard
mask is filled in with zero’s in the network and subnet portions and one’s in the
host portion except the last bit (this determines odd or even…it’s the “1” bit):
00000000.00000000.00000000.00011110
Therefore, when we convert this wildcard mask back to decimal we get a wildcard
mask of 0.0.0.30 for our subnet wildcard mask. This one can be confusing…later
on when you learn about writing access control lists doing something like this will
depend upon whether you are permitting or denying something. For now just
realize the bits do not have to be contiguous.
Supplemental Labs or Challenge Activities:
1. Write a wildcard mask that will mask the 192.168.1.0/24 network. We are
looking for an exact match of the network and subnet portions only.
2. Write a wildcard mask that will mask the host portions of the 192.168.1.0/24
network. We are looking for an exact match of the host portions only.
3. Write a wildcard mask that will mask the odd ip addresses of the
172.16.23.0/16 network. We are looking for an exact match of the network,
subnet and odd-numbered ip’s in the host portion.
4. Write a wildcard mask that will mask the upper half of the 10.128.0.0/11
network. Here we will mask 129-255 in the second octet and 0-255 in the
third and fourth octets (so we need exact matches for them).
5. Write a wildcard mask that will mask the lower half of the 200.210.128.0/27
network. Here we need to mask the lower half of the host portion for the 128
subnet.
**as I said these are subjective in respect to the needs of the access control list**
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