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New To CCNA

Emissary_of_Pain

Good Day ...

I recently (8th on Jan) started studying for my CCNA ... I am going through e-Careers and was assured that CCNA can be done by anyone as it starts from the most basic and works its way up ... ... Needless to say I feel that was just a play to get a sale ...

I have 2 quick questions that I really just can't wrap my head around ... Sorry if these sound stupid but I could really use some advice as I have never done any form of networking apart from setting up small star networks and home networking ... (never studied networking at all so it is all new to me)

1) What exactly is a "broadcast domain" ...

Would I be correct in saying that a Broadcast Domain would be the equivalent to an entire office on the floor of a building and then that would be broken up into smaller networks (collision domains) using subnetting for each department in that specific office ?

2) I am currently confused with subnetting and determining the maximum number of hosts...

If the IP address and Subnet Mask is as follows : 192.168.0.96 255.255.255.192
The Base2 IP address would be : 11000000.10101000.00000000.01100000
The Base2 S.Mask would be : 11111111.11111111.11111111.11000000

This shows that the subnet has an increment of 64 meaning that the subnets will be as follows

0 64 128 192
1 65 129 193
2 66 130 194
. . . .
. . . .
. . . .
63 127 191 255

The fourth increment cannot exceed 255 so it stops at 255.

Is this correct ??

If I assume it is correct to work out the maximum number of hosts on that subnet I would say

2^H-2
2^6-2 = 62

I can have a maximum of 62 hosts on that network/subnet but this contradicts the maximum increment of 64 and if we include 0 as an address meaning 2^6-1 = 63 which is correct …

What is the correct formula for the number of hosts per increment ???

All Information would be greatly appreciated.
Kind Regards,
Richard.

:::EDIT:::
I apologize for the formatting ... It went all messed up for some reason ... lol

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Comments

fadhil

for subnetting:
0 64 128 192 these are subnets ID or network ID.
1 65 129 193 these are the first address for each subnet and the first valid host for each subnet eg of network 128 the first address is 129
63 127 191 25 these are broadcasts address for each subnet eg for 65,the broadcast is 127.
so it is fine, i mean you are right.
for host
the correct formula for number of host per increment is 2^h -2.

iamme4eva

A broadcast domain is a portion of your network where the broadcast will be sent if one host sends a broadcast (a message to all other hosts). Typically this is all hosts connected together by switches. Broadcast domains are seperated by using VLANS on the switches, or by using routers.

A collision domain is a portion of your network where multiple hosts could transmit at the same time, causing a collision (look up CSMA/CD in your books or on google). In modern switched networks, these are pretty much non-existant, as the collision domain is from the host to the switch - a switch intelligently forwards packets based on MAC addresses. However, if hubs or repeaters are being used, then the collision domain would be any host connected to the hub. Collision domains are seperated by switches / bridges.

BobMead

You can think of a broadcast domain =subnet= vlan

BobMead

Get the Cisco Press books and read them. But just tell your self that this will make me better. IT is great because you can read a book apply the knowledge and change your life. You can do this!

MrXpert

Normally in a company you will have a switch setup with several VLANS. Each VLAN represents a broadcast domain or an IP subnet. For example you could have VLAN Accounts which is on 192.168.10.0/24 and VLAN Sales on 192.168.11.0/24. They are in different broadcast domains and if a host 192.168.10.5/24 was to send a broadcast packet (255.255.255.255 or FFFF.FFFF.FFFF) then only hosts within that accounts subnet would hear it. Routers won't forward on broadcasts. If a host in Accounts wants to communicate with a host in Sales then a router or multi layer switch is needed for the inter vlan routing. If you plug in a PC into a switch then it will be on its own collision domain meaning it can only collide with itself because there is a one to one mapping between the port and the host's mac address.

With the subnetting stuff, I would highly recommend Todd Lamle's Network+ book (if you can get hold of it) as it explains subnetting very clearly and has lots of practice questions. When I was learning subnetting his method was the only one that seemed to make sense and i found myself referring to it when I was doing CCENT.

I don't know if you know about these but they are good practice links
Subnetting Quiz #1
Subnetting Quiz #2 (CIDR)
subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online (the questions involving max number of hosts/subnets are not always correct.bear that in mind)
Check out Cisco Binary game to improve your binary skills
Humphrey from Router Gods has a excellent timer based subnetting program on his website/gns3 topologies/misc section you can download free of charge.

Emissary_of_Pain

WOW ...

Thank you for the great responses and I apologize for the late response myself ... My ISP was having major issues.

@fadhil

Thanks for explaining it a bit better than the online course did ... the guy speaks in monotone and I could swear he was just given a printout to read through as quick as possible ... lol ...

So the -2 part of the equation is basically for the Subnet ID and Broadcast Address for each increment which is the very very first number (the actual increment) and the last possible address before the next increment, seems you can't assign a host to these addresses we remove them meaning an increment of 64 can only have 62 hosts ...

@iamme4eva & MrXpert

Thank you both for explaining the Broadcast Domains, especially the example you gave MrXpert. I actually understand the whole scenario now (MrXpert basically dumbed it down for me using "pictures" ... lol)

I didn't know about those Links and I will try get my hands onto Todd Lamle's Network+ book ...

I appreciate all the help so far !
Regards,
Richard.

swild

This has been posted before on these forums, but I felt that this was one of the best resources that I used during my studying: Free Streaming Bootcamps from INE.

I wound up using a whole lot of books before passing the ICND2 exam on my 4th attempt, but Odom's Cisco Press books and this INE source were the best.

iamme4eva

Emissary_of_Pain wrote: »

So the -2 part of the equation is basically for the Subnet ID and Broadcast Address for each increment which is the very very first number (the actual increment) and the last possible address before the next increment, seems you can't assign a host to these addresses we remove them meaning an increment of 64 can only have 62 hosts ...

You are correct.

Emissary_of_Pain

I thought I would ask my next question here instead of making a new thread to try save on making tons of threads ...

When subnetting, every one has different charts or methods they use ... ... of the 2 charts in the attached image ... which would you say is the better chart ...

Subnetting Chart.jpg

boredgamelad

It is really up to you to decide; what works best is going to be different for each person depending on how they've learned subnetting. FWIW, I use a simplified version of the upper right portion of that chart. It's quick to write out and easy to remember, and if you really have to apply it to a Class B or class A network you just need to be able to multiply by 2.

iamme4eva

What boredgamelad said...

It's whatever you find easiest. As long as you get the answer, there is no right or wrong method.

I write something similar to the top table, but only for the last octet.

Emissary_of_Pain

Thanks so much for the replies ... ...

I guess I am just battling to grasp the subnetting thing ... I just when I think I understand it I get a question that throws me for a loop ... haha ...

I know I just started the section but it is still frustrating ...

iamme4eva

You get plenty of practice, don't worry about that! You'll find it will just all click into place eventually - and if you are doing it often enough you pick up the common ones without needing to do the maths.

www.subnettingquestions.com is a good way to kill ten minutes if you need some practice.

Emissary_of_Pain

That is the site I am using for testing myself ... as I am studying online there isn't really any proper exercises or practice ... so I look for all the sites I can posting questions about the module I am currently on ...

Emissary_of_Pain

Hey all ...

I am doing the multiple question thing again to try avoid creating needless threads ...

I just wanted to find out if there are any good and preferably free Router Simulators ... I just priced some routers in my country and yeah ... simulators for now would be a great idea to learn the commands ... lol