exam
Written on 10:40 by Ahmet Emir
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Subnetting in Your Head: Class B Addresses
Written on 23:25 by Ahmet Emir
Are you nuts? Subnet Class B addresses in our heads? It’s absolutely easier than autograph it out—
I’m not kidding! Let me appearance you how:
Question: What subnet and advertisement abode is the IP abode 172.16.10.33
255.255.255.224 (/27) a affiliate of?
Answer: The absorbing octet is the fourth octet. 256 – 224 = 32. 32 + 32 = 64. Bingo: 33
is amid 32 and 64. However, bethink that the third octet is advised allotment of the
subnet, so the acknowledgment would be the 10.32 subnet. The advertisement is 10.63, back 10.64 is
the abutting subnet. That was a appealing accessible one.
Question: What subnet and advertisement abode is the IP abode 172.16.66.10
255.255.192.0 (/18) a affiliate of?
Answer: The absorbing octet is the third octet instead of the fourth octet. 256 – 192 = 64.
0, 64, 128. The subnet is 172.16.64.0. The advertisement charge be 172.16.127.255 since
128.0 is the abutting subnet.
Question: What subnet and advertisement abode is the IP abode 172.16.50.10
255.255.224.0 (/19) a affiliate of?
Answer: 256 – 224 = 0, 32, 64 (remember, we consistently alpha counting at aught (0)). The subnet
is 172.16.32.0, and the advertisement charge be 172.16.63.25 back 64.0 is the abutting subnet.
Question: What subnet and advertisement abode is the IP abode 172.16.46.255
255.255.240.0 (/20) a affiliate of?
Answer: 256 – 240 = 16. The third octet is absorbing to us. 0, 16, 32, 48. This subnet
address charge be in the 172.16.32.0 subnet, and the advertisement charge be 172.16.47.255
since 48.0 is the abutting subnet. So, yes, 172.16.46.255 is a accurate host.
Question: What subnet and advertisement abode is the IP abode 172.16.45.14
255.255.255.252 (/30) a affiliate of?
Answer: Where is the absorbing octet? 256 – 252 = 0, 4, 8, 12, 16 (in the fourth octet).
The subnet is 172.16.45.12, with a advertisement of 172.16.45.15 because the abutting subnet is
172.16.45.16.
Question: What is the subnet and advertisement abode of the host 172.16.88.255/20?
Answer: What is a /20? If you can’t acknowledgment this, you can’t acknowledgment this question, can you?
A /20 is 255.255.240.0, which gives us a block admeasurement of 16 in the third octet, and back no
subnet $.25 are on in the fourth octet, the acknowledgment is consistently 0 and 255 in the fourth octet.
0, 16, 32, 48, 64, 80, 96…bingo. 88 is amid 80 and 96, so the subnet is 80.0 and the
broadcast abode is 95.255.
Question: A router receives a packet on an interface with a destination abode of
172.16.46.191/26. What will the router do with this packet?
Answer: Abandon it. Do you apperceive why? 172.16.46.191/26 is a 255.255.255.192 mask,
which gives us a block admeasurement of 64. Our subnets are again 0, 64, 128, 192. 191 is the broadcast
address of the 128 subnet, so a router, by default, will abandon any advertisement packets.
Practice Example #8B: 255.255.255.224 (/27)
Written on 23:24 by Ahmet Emir
This is done the aforementioned way as the above-mentioned subnet mask, except that we aloof accept added subnets
and beneath hosts per subnet available.
172.16.0.0 = Network address
255.255.255.224 = Subnet mask
Subnets? 211 = 2048.
Hosts? 25 – 2 = 30.
Valid subnets? 256 – 224 = 32. 0, 32, 64, 96, 128, 160, 192, 224.
Broadcast abode for anniversary subnet?
Valid hosts?
The afterward table shows the aboriginal eight subnets:
Subnet 0.0 0.32 0.64 0.96 0.128 0.160 0.192 0.224
First host 0.1 0.33 0.65 0.97 0.129 0.161 0.193 0.225
Last host 0.30 0.62 0.94 0.126 0.158 0.190 0.222 0.254
Broadcast 0.31 0.63 0.95 0.127 0.159 0.191 0.223 0.255
This abutting table shows the aftermost eight subnets:
Subnet 255.0 255.32 255.64 255.96 255.128 255.160 255.192 255.224
First host 255.1 255.33 255.65 255.97 255.129 255.161 255.193 255.225
Last host 255.30 255.62 255.94 255.126 255.158 255.190 255.222 255.254
Broadcast 255.31 255.63 255.95 255.127 255.159 255.191 255.223 255.255
Practice Example #7B: 255.255.255.192 (/26)
Written on 23:23 by Ahmet Emir
Now, this is area Class B subnetting gets easy. Since the third octet has a 255 in the mask
section, whatever cardinal is listed in the third octet is a subnet number. However, now that
we accept a subnet cardinal in the fourth octet, we can subnet this octet aloof as we did with
Class C subnetting. Let’s try it out:
172.16.0.0 = Network address
255.255.255.192 = Subnet mask
Subnets? 210 = 1024.
Hosts? 26 – 2 = 62.
Accurate subnets? 256 – 192 = 64. The subnets are apparent in the afterward table. Do these
numbers attending familiar?
Broadcast abode for anniversary subnet?
Accurate hosts?
The afterward table shows the aboriginal eight subnet ranges, accurate hosts, and broadcast
addresses:
Subnet 0.0 0.64 0.128 0.192 1.0 1.64 1.128 1.192
First host 0.1 0.65 0.129 0.193 1.1 1.65 1.129 1.193
Last host 0.62 0.126 0.190 0.254 1.62 1.126 1.190 1.254
Broadcast 0.63 0.127 0.191 0.255 1.63 1.127 1.191 1.255
Notice that for anniversary subnet amount in the third octet, you get subnets 0, 64, 128, and 192 in
the fourth octet.
Practice Archetype #6B: 255.255.255.128 (/25)
Written on 23:22 by Ahmet Emir
This is one of the hardest subnet masks you can comedy with. And worse, it absolutely is a really
good subnet to use in assembly because it creates over 500 subnets with 126 hosts for each
subnet—a nice mixture. So, don’t skip over it!
172.16.0.0 = Network address
255.255.255.128 = Subnet mask
Subnet 0.0 2.0 4.0 6.0 8.0
First host 0.1 2.1 4.1 6.1 8.1
Last host 1.254 3.254 5.254 7.254 9.254
Broadcast 1.255 3.255 5.255 7.255 9.255
Subnet 0.0 1.0 2.0 3.0 ... 254.0 255.0
First host 0.1 1.1 2.1 3.1 ... 254.1 255.1
Last host 0.254 1.254 2.254 3.254 ... 254.254 255.254
Broadcast 0.255 1.255 2.255 3.255 ... 254.255 255.255
Subnetting Basics 131
Subnets? 29 = 512.
Hosts? 27 – 2 = 126.
Accurate subnets? Okay, now for the catchy part. 256 – 255 = 1. 0, 1, 2, 3, etc. for the third
octet. But you can’t balloon the one subnet bit acclimated in the fourth octet. Remember back I
showed you how to amount one subnet bit with a Class C mask? You amount this the same
way. (Now you apperceive why I showed you the 1-bit subnet affectation in the Class C section—
to accomplish this allotment easier.) You absolutely get two subnets for anniversary third octet value, hence
the 512 subnets. For example, if the third octet is assuming subnet 3, the two subnets
would absolutely be 3.0 and 3.128.
Broadcast abode for anniversary subnet?
Accurate hosts?
The afterward table shows how you can actualize subnets, accurate hosts, and broadcast
addresses application the Class B 255.255.255.128 subnet affectation (the aboriginal eight subnets are shown,
and again the aftermost two subnets):
Subnet 0.0 0.128 1.0 1.128 2.0 2.128 3.0 3.128 ... 255.0 255.128
First
host
0.1 0.129 1.1 1.129 2.1 2.129 3.1 3.129 ... 255.1 255.129
Last
host
0.126 0.254 1.126 1.254 2.126 2.254 3.126 3.254 ... 255.126 255.254
Broadcast
0.127 0.255 1.127 1.255 2.127 2.255 3.127 3.255 ... 255.127 255.255
Practice Example #5B: 255.255.255.0 (/24)
Written on 23:21 by Ahmet Emir
Contrary to accustomed belief, 255.255.255.0 acclimated with a Class B adjustment address is not declared a
Class B adjustment with a Class C subnet mask. It’s amazing how abounding bodies see this affectation used
in a Class B adjustment and ahead it’s a Class C subnet mask. This is a Class B subnet affectation with
8 $.25 of subnetting—it’s appreciably adapted from a Class C mask. Subnetting this address is
fairly simple:
172.16.0.0 = Adjustment address
255.255.255.0 = Subnet mask
Subnets? 28 = 256.
Hosts? 28 – 2 = 254.
Authentic subnets? 256 – 255 = 1. 0, 1, 2, 3, etc., all the way to 255.
Broadcast address for ceremony subnet?
Authentic hosts?
The after table shows the ancient four and aftermost two subnets, the authentic hosts, and the
broadcast addresses in a Class B 255.255.255.0 mask:
Subnet 0.0 1.0 2.0 3.0 ... 254.0 255.0
First host 0.1 1.1 2.1 3.1 ... 254.1 255.1
Last host 0.254 1.254 2.254 3.254 ... 254.254 255.254
Broadcast 0.255 1.255 2.255 3.255 ... 254.255 255.255
Practice Example #4B: 255.255.254.0 (/23)
Written on 11:36 by Ahmet Emir
- Subnets? 27 = 128.
- Hosts? 29 – 2 = 510.
- Accurate subnets? 256 – 254 = 0, 2, 4, 6, 8, etc., up to 254.
- Advertisement abode for anniversary subnet?
- Accurate hosts?
172.16.0.0 = Network address
255.255.254.0 = Subnet mask
Subnet 0.0 64.0 128.0 192.0
First host 0.1 64.1 128.1 192.1
Last host 63.254 127.254 191.254 255.254
Broadcast 63.255 127.255 191.255 255.255
Subnet 0.0 16.0 32.0 48.0
First host 0.1 16.1 32.1 48.1
Last host 15.254 31.254 47.254 63.254
Broadcast 15.255 31.255 47.255 63.255
130 Chapter 3 Subnetting, VLSMs, and Troubleshooting TCP/IP
The afterward table shows the aboriginal bristles subnets, accurate hosts, and advertisement addresses in a
Class B 255.255.254.0 mask:
Subnet 0.0 2.0 4.0 6.0 8.0
First host 0.1 2.1 4.1 6.1 8.1
Last host 1.254 3.254 5.254 7.254 9.254
Broadcast 1.255 3.255 5.255 7.255 9.255