Help 1

[mcintosh78]

Ok, SO I am already into chapter 4 of the Cisco systems CCNA Intro book and I am having a little bit of a hard time with the termins and how to associate them to the telecom world so I understand them. Any suggestions or help would be great.
Thanks

 

[burtsbees]

For example???

Burt

 

[mcintosh78]

Well, I am trying the labs that came with the Cisco CCNA book (Boson) and the labs on free-labs.com and I guess I need the line by line solution to each problem. More so I know why I am doing what I am doing, then how to do it.
I understand routers, switches and the idea of what a server does. I know how to program a router in the small computer network realm.

Can you or anyone relate items like Datalink to the telephony world??
And the whole subnet thing just confuses the crap out of me.
Thanks

 

[burtsbees]

The whole subnetting thing confuses the crap out of most people at first.
The datalink in the seven layer OSI model---I can't really think of a good comparison...then again, I am not a phone dude.

Burt

 

[CiscoGuy33]

mcintosh78,
As Burt said subnetting is always one of the hardest parts to grasp!

CCNA can be very overwelming - even to people with some background in networking - there is a lot to know and understand

I would very highly advise that you also get the Sybex CCNA Study Guide by Todd L. to go with your Cisco CCNA book. His chapter on subnetting is one of the best out there and the whole book covers CCNA very well.

You can download the subnetting chapter here in a free book preview -

http://www.bookpool.com/sm/0782143911

You also might want to look at one of the "CCNA for Dummies" or "Cisco for Dummies" or "Networking for Dummies" - I love these books because you can read them very quickly and then you have a VERY simple understanding of the subject! And since they are trying to simplify the subject they have explantions that are hard to beat

You could never pass a test with one but for a very quick overall picture - they are great!

Hope this helps!


E.A. Broda
CCNA, CCDA, CCAI, Network +

 

[lerdalt]

One of the best Dummies books I picked up was "Firewalls for Dummies" it had a great section on the OSI, that I thought was one of the best intro's into it that I've ever read.

The best thing to do though when it comes to subnetting is practice. I did some web searches and stumbled across some course notes that had some excellent examples with answers to work through.

 

[mcintosh78]

Thanks for the help. Next question. If there is instructions to asign an ip address xxx.xxx.xxx.xxx and then "/24", what does that mean and how do you accomplish that? Is that part of the subnetting??

 

[burtsbees]

The /24 means there are 24 bits in the subnet mask, or 255.255.255.0
router>en
router#conf t
router(config)#int fa0/0
router(config-if)#ip add 192.168.1.1 255.255.255.0
Like that. The number after the slash is the number of bits in the network portion of the subnet mask. If it were /21, for example, then it would be 255.255.248.0
In binary, it would be
11111111.11111111.11111000.00000000, which = 255.255.255.448 in decimal form.
The subnet mask is 32 bits, and all the leftover bits are 0
Count the one's...in /24, there are 24 out of 32 bits that are set to 1, all occuring in "octets", or 8 at a time, separated by dots...
So a /24 is
11111111.11111111.11111111.00000000
Post back if you need more help, like on how exactly the mask determines what bits in the address itself are network bits and which are host bits.

Burt

 

[burtsbees]

I typed 255.255.255.448 on accident---it is supposed to be 255.255.255.248

Burt

 

[mcintosh78]

burtsbees
Thanks in advance. I just read that out loud to my wife and I think I just got the strangest look ever..
Is there an online or downloadable converting calculator for IP to decimal??
Thanks

 

[mcintosh78]

Also, can you have a subnet with like 255.200.255.255. and if so, how do you change that??

 

[lerdalt]

Solarwinds has an excellent subnet calculator, but I'm not certain it's free.

As for the 255.200.255.255 mask, that's not going to work. You have to work left to right as far as the most vs. least significant bits. Todd Lammle's books do a far far better job explaining it all than what I could ever hope to do here. I strongly suggest learning how to subnet with the binary math. It does make all the pieces fall together better later.

 

[burtsbees]

Exactly---like lerdalt says, you should really work it out yourself. You'll get the hang of it, trust me. Practice makes perfect---soon, you'll be doing it in your sleep. You think you get strange looks now...ha ha.

Burt

 

[mcintosh78]

Thank you guys. I actually get it now. Its like using the same area code within a given area, but using the translations within the switch to direct the calls, for either area A or area B.

 

[lerdalt]

that sounds like a pretty good relation to the telecom world to me. I wish I understood more of the telecom stuff to relate it to better for you.

I have been trying to sit back and try to think how I could describe some of the osi stuff to telephones, but really haven't come up with anything good yet, other than this:
layer 1 - physical cabling
layer 2 - having dialtone when phone goes off hook
layer 3 - how the phone switch routes the calls between switches.

 

[burtsbees]

Well, subnetting would be like borrowing a number or two from the prefix and adding it to the area code---it gives you more leeway for the area, but less for the number of phone numbers that can be derived.

Burt

 

[eurobadger]

I used the subnet calculator from:

http://www.boson.com/FreeUtilities.html

The config register calculator is interesting too.

Both are free.

EB