Access list - wildcards

The Lammle book has me a little confused on the wildcards.

He has 172.16.16.0 0.0.3.255 as covering 172.16.16.0 through 172.16.19.0. Does he mean 172.16.16.0 - 172.16.19.255?

Same with 172.16.16.0 0.0.7.255 as covering 172.16.16.0 through 172.16.23.0. Does he mean 172.16.16.0 - 172.16.23.255

Cheers

Charlie.

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Comments

tech-airman

VantageUK,

VantageUK wrote: »

The Lammle book has me a little confused on the wildcards.

He has 172.16.16.0 0.0.3.255 as covering 172.16.16.0 through 172.16.19.0. Does he mean 172.16.16.0 - 172.16.19.255?

What is the wildcard mask of 0.0.3.255 in binary?

VantageUK wrote: »

Same with 172.16.16.0 0.0.7.255 as covering 172.16.16.0 through 172.16.23.0. Does he mean 172.16.16.0 - 172.16.23.255

What is the wildcard mask of 0.0.7.255 in binary?

VantageUK wrote: »

Cheers

Charlie.

VantageUK

I'm not sure what you're asking.

Well, to rephrase, I know what you're asking, but I'm not sure why you're asking it?

What I'm after is when Lammle says a wildcard covers networks 172.16.16.0 through 172.16.19.0, does he mean that it covers ALL of the available IPs in the networks?

ie: all the way up to 172.16.19.255.

tech-airman

VantageUK wrote: »

I'm not sure what you're asking.

Well, to rephrase, I know what you're asking, but I'm not sure why you're asking it?

What I'm after is when Lammle says a wildcard covers networks 172.16.16.0 through 172.16.19.0, does he mean that it covers ALL of the available IPs in the networks?

ie: all the way up to 172.16.19.255.

VantageUK,

If you know what I'm asking, feel free to answer my questions.

mzinz

VantageUK wrote: »

I'm not sure what you're asking.

Well, to rephrase, I know what you're asking, but I'm not sure why you're asking it?

What I'm after is when Lammle says a wildcard covers networks 172.16.16.0 through 172.16.19.0, does he mean that it covers ALL of the available IPs in the networks?

ie: all the way up to 172.16.19.255.

The problem is that you're thinking about subnetworks as ALWAYS having 255 hosts. This isn't always the case. A subnet will only have 255 hosts if it is 255.255.255.0 (or 0.0.0.255 in this case).

The size of a subnet depends on the network mask, right?

The reason that Vantage was having you convert to binary is because you can determine how many hosts are in a subnet by doing so.

0.0.3.255 in binary = 0000000.00000000.00000011.11111111

Ok, so we know that 0 bits are part of the subnet. Now let's convert that IP to binary.

172.16.16.0 in binary = 10101100.00010000.00010000.00000000

Now, any spot in the wildcard mask that has a 0 is part of the SUBNET.
10101100.00010000.00010000.00000000 = 172.16.16.0 <----Network address
00000000.00000000.00000011.11111111 = 0.0.3.255 <----Wildcard mask

10101100.00010000.00010000.00000000 = 172.16.16.0 <----Subnet Start
10101100.00010000.00010011.11111111 = 172.16.19.255 <----Subnet End

See what we did there? Now, keep in mind, this is ONE SUBNET! So theoretically you could use any IP from 172.16.16.1 to 162.16.19.254!

So lets say you just wanted to calculate how many hosts are in this single subnet. You can do that JUST by having the wildcard mask (or subnet address)!
0.0.3.255 = 00000000.00000000.00000011.11111111. Ok, so that is TEN 1's in a row. Using simple binary, let's calculate what that comes out to:
2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 <

Ten bits in binary equals 1024!! That means that we have 1022 usable IPs (one for subnet and one for broadcast)!