Quick Subnetting Question

NetstudentNetstudent Posts: 1,694Member
I'm going through the questions on www.subnettingquestions.com

They have :

Question: How many subnets and hosts can you get from the network 172.16.0.0/24?

Answer: 256 subnets and 254 hosts

I understand that they are using classfull subnetting, so I guess my question is how am I supposed to know when to use classfull subnetting and when to use classless? Will the question mention CIDR? If the question reads:

How many subnets and hosts can you get from the CIDR block 172.16.0.0/24?

Would the answer be the same?
There is no place like 127.0.0.1 BUT 209.62.5.3 is my 127.0.0.1 away from 127.0.0.1!

Comments

  • kafifi13kafifi13 Posts: 259Member
    I ran into the same problem. ON the exam will it tell you to subnet using classless?
  • ignign0ktignign0kt Posts: 42Member ■■□□□□□□□□
    The network is classful if it uses a default network mask. /8 for class A, /16 for class B, and /24 for class C. Anything else is going to be classless and therefore using CIDR
  • malcyboodmalcybood Posts: 900Member
    Following on from what ignidn0kt said, if the specified address combined with subnet mask, is anything other than the below default values then you are using a classless address. Being able to determine that the address is classless, knowing host ranges of subnets, network and broadcast addresses is part of the exam objectives.

    Class A
    Address Range = 0.0.0.0 - 126.255.255.255
    CIDR = /8
    Default Subnet Mask - 255.0.0.0

    Class B
    Address Range = 128.0.0.0 - 191.255.255.255
    CIDR = /16
    Default Subnet Mask - 255.255.0.0

    Class C
    192.0.0.0 - 223.255.255.255
    CIDR = /24
    Default Subnet Mask - 255.255.255.0

    Once you learn subnetting properly you will be able to tell if an address is classful by combining network address & subnet mask.

    For example a network address of 199.167.3.1 with subnet mask of 255.255.255.0 is a classful class C address as the first octet is 199 (falls inbetween 192 - 223). The network address here would be 199.167.3.0 and the broadcast 199.167.3.255 leaving .1 - .254 as usable hosts.

    The same network address of 199.167.3.1 with a subnet mask of 255.255.255.252 is classless as you have used a /30 or .252 CIDR block. The network address would be 199.167.3.0 and the broadcast would be 199.167.3.3 leaving .1 and .2 as usable hosts
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