People i need help seriously !:( *Cisco Packet Tracer*

mindzfreak

I was asked to calculate 172.16.222.41 /24... But may i know what's the " /24 " supposed to mean..? and i was also asked by my lecturer to calculate 24 host... How do i actually calculate it..? im really lost Need explanation from you guys out there Any help would be appreciated

swild

http://www.techexams.net/forums/ccna-ccent/14104-techexams-net-ip-subnet-calculator-windows-v1-0-a.html

Also, Lammle has a pretty good method for doing it in your head if you want to check out his CCNA Study Guide.

It's been about a year since I looked at it and I don't have it on my desk at the moment or I could give you details. Sorry.

the /24 is the short notation for the subnet mask.

mindzfreak

swild wrote: »

http://www.techexams.net/forums/ccna-ccent/14104-techexams-net-ip-subnet-calculator-windows-v1-0-a.html

Also, Lammle has a pretty good method for doing it in your head if you want to check out his CCNA Study Guide.

It's been about a year since I looked at it and I don't have it on my desk at the moment or I could give you details. Sorry.

the /24 is the short notation for the subnet mask.

Hmm the Ip Subnet Calculator does everything? it can calculate everything regarding ip/subnet etc.. ? included what i mentioned above? by the way, may i know what do you actually meant by Short notation for subnet ?

bermovick

What swild says. /24 is just an easier way to write 255.255.255.0. Count the number of 'on' bits in 255.255.255.0 and you'll see the answer is ... 24!

So 255.255.0.0 would be /16. A nice 255.255.255.252 serial link is /30. You get the idea.

zrockstar

Don't rely on a subnet calculator. If you want any chance at all of getting a cert, even N+, you are going to need to know some degree of subnetting. If you want CCENT or CCNA, you are going to have to know it like the back of your hand. If you are in a class that grants you packet tracer access, that means that you probably at a minimum have access to the unit modules through netacad, or at least your instructor can provide it. You cannot get through this material just doing the homework/PT. You HAVE to do the book work, online module, then utilize external resources as well.

swild

If you don't know what a subnet is, then you need to go back and revisit some earlier lessons. If your teacher hasn't covered subnets and subnetting, yet expects you to be able to answer those questions, I would complain to the department chair. That's a fairly complicated topic to throw at you out of the blue.

Chapter 4 in Amazon.com: CCNA Cisco Certified Network Associate Deluxe Study Guide, (Includes 2 CD-ROMs) (9780470901083): Todd Lammle: Books lays out subnetting in the simplest terms I have been able to find. A lot of other texts I found were harder to follow.

Good Luck!

Ltat42a

Here are some decent videos on subnetting and some challenges in Packet tracer.

Cisco CCNA 1 - YouTube

Cisco CCNA 2 - YouTube


hth

computer g33k

Check this out. IPv4 Subnetting TechNotes

mindzfreak

Hmm....i still dont quite understand what you guys are trying to say...but really thanks though..appreciated.. but may i know if a question asked "How many bits are there in 29 host?" how do i calculate it...?

Roguetadhg

How many bits are there in 29 host?

Are you trying to find the smallest network mask that'll give you 29 hosts?

The way to find a smallest host is to think of this small map. Write it down, you'll memorize it as a side-effect of working with the numbers. You'll get faster and faster when doing subnetting. Don't worry about pounding numbers into your head. It'll come with practicing.

1. 128 | 64 | 32 | 16 | 8 | 4 | 3 | 2 |1.
This represents the final 8 bits in an address. Ie: (x.x.x.0000 0000)
128 | 64 | 32 | 16 | | 8 | 4 | 3 | 2 |1.
N | N | N | N | | N | N | N | N.
0000 0000

2. With the above mapping done write down which number can be subtracted from 29 without giving a negative number.
2. What is the highest number that'll fit within the host number.

Answer: 16
3. Write a X at the 16th bit and all the rest to the right of it.. I'm coloring the bits i've mentioned green:
128 | 64 | 32 |16 | 8 | 4 | 3 | 2 |1. = Green are Host Bits
N | N | N | H | H | H | H | H | H.

4. The first number to the left of the 16th bit would be the last bit of the subnet mask.
4. The last Red number is the last subnet bit. That's the 32nd bit.

5. Keep in mind that a network address has three types of addresses: Network, Valid, and Broadcast.
a. Network address would be all the green bits turned "off" and turned to a "Zero".
Example: NNN|00000
b. Broadcast: All green bits turned "On" and turned to a "One"
Example: NNN|11111
c. Valid addresses are all the addresses starting from the first, to the last inbetween the Network and Broadcast:
Example: NNN|00001 toNNN|11110

What does this matter? Because there's only a certain amount of addresses you would be able to give within a subnetwork. Look back at the number of green host bits:
128 | 64 | 32 |16 | 8 | 4 | 3 | 2 |1.
You'll be able to a total of 32 addresses from 5 bits. Don't believe me? Starting from the XXX|00000 Address (It counts at the first one)...

00000 - Network Address. Larger picture: 00000000
00001 - First available usable address: 00000001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
01101
01110
01111
10000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
11101
11110 - First available usable address: 00011110
11111 - Broadcast Address: 00011111
I]I made sure to count them, so I didn't forget a 1/0 somewhere :P[/I

In short, the quickest way to figure out how many usable HOST (Addresses that can be assigned to a host or interface) addresses there is to take the Last red number, the final subnet bit and subtract 2 (1 for network and 1 for broadcast)
128 | 64 | 32 |16 | 8 | 4 | 3 | 2 |1.
32 - 2 = 30. 30 usable host addresses
To find the number of subnets available. Just don't subtract 2. The way I think about finding subnets is this:

I erase the number of bits that are dedicated to hosts (5 in this case). This leave 3 bits that dedicated for subnets.
128 | 64 | 32 | 16 | 8 | 4 | 3 | 2 |1.
Using the same host-finding principle, I look at the last number that is NOT a subnetwork. This is the 4th number. There are 4 available subnets.

Subnet-Zero: Keep in mind this is with the "Subnet-Zero" enabled. However, if "Subnet-Zero" is disabled: Find Subnets like Hosts and subtract 2 from the number. In this case 2. Always assume that "Subnet-Zero" is enabled and on. The problem will state that Subnet-Zero has been disabled.

4 Subnets with Subnet-Zero enabled.
2 Subnets with Subnet-Zero disabled.

To find the network mask:
1. Add the red subnetwork bits together. 128 + 64 + 32 = 224.
128 | 64 | 32 |16 | 8 | 4 | 3 | 2 |1.
The subnet mask is: 255.255.255.224
Written in CIDR notion: /27 [8bits + 8bits + 8bits + 3bits]

2. Convert the subnet mask into binary and you'll see the big picture:
1111 1111. 1111 1111. 1111 1111. 1110 0000

Each of those bits (1s and 0s) has a designated number (128,64,32,16,8,4,2,1). These numbers makes binary easier for us humans to work with.


You'll need to be able to do subnetting on a dry-erase pad, at minimal. But you'll need to get a firm mastery of the topic and be able to do it confidently, correctly and quickly. The amount of time you can shave off for doing Subnetting will give you more time to think through labs.
Practice Site I use: http://faculty.valleycollege.net/rpowell/jscript/subnet2.htm.

cmitchell_00

Nice study site

THA_DOC

Thanks, that was very helpfull!!

Ltat42a wrote: »

Here are some decent videos on subnetting and some challenges in Packet tracer.

Cisco CCNA 1 - YouTube

Cisco CCNA 2 - YouTube


hth

Ltat42a

THA_DOC wrote: »

Thanks, that was very helpfull!!

Yer welcome, that guy uses Packet Tracer quite a bit in his CCNA course.
Here's his Playlist, CCNA 1- 4, + Security

danscourses's Channel - YouTube