WHEN IN THE WORLD WILL I NEED THIS?!? ICND1 6

[bobbyforhire]

Ok so i picked up a few videos and i'm getting to the subnetting. I have been watching these videos like i'm going to die if i don't watch 24hours of video in a week.


So i get the concept of subnetting but lets be honest when am I or a company going to need 40 networks with with only two useable host bits?

A question i was asked was to find out the range of ip's you can use for a network requiring 40 networks on an ip of 200.1.1.0 running on a class C network.

So, after coming up with the answer of 200.1.1.0-200.1.1.3 and a subnet of 255.255.252.0. So i can't use the 1.0 and i can't use the 1.3 so that only gives me 2 ip's that i can use on that network.

Has anyone ever had to deal with 20 routers at the same time? (this is good for a router->router connection) I understand that this is just good learning but i have meet alot of network admins and they have never used this math to get the answer. So should i start using this math and any pointers on getting the solution that i came up with to save any time?

 

[bobbyforhire]

Sorry if none of that really adds up as it's 2:00am and i've been hitting the books non-stop

 

[DallasBPF]

you need it for the cisco exam.... plain and simple... it is awesome experience just getting to know subnetting

------------------------------------
Dallas, Texas
Telecommunications Tech
CCVP, CCNA, Net+

CCNP in the works

 

[Cluebird]

Historically, the number one problem with IP networks was poorly assigned address space that could not be summarized on Core routers in the network to improve efficiency. Understanding how the address space is used is key to basic networking. If you're ever asked to renumber an IP network, subnetting knowledge is key.

I have seen an admin given 6 months to figure out a new address scheme for a network. When he had to present his new plan for implementation he finally admitted he didn't know what he was doing and needed a contractor to do the work. Management didn't fire him (as they should have) but paid a contractor big bucks to do the addressing. The actual addressing scheme wasn't complex and I wished I was that contractor because I figured out a scheme in two minutes. The bill the company paid was nearly $5000.

When I get learners complaining about subnetting, I boil it down to this: If you want to pass CCNA you must know subnetting cold. It's Cisco's exam and Cisco's cert. They think subnetting is a foundational skill so it is a make or break topic for CCNA. If you don't care about certs, don't learn subnetting. If you do care about certs, learn it cold. You can be weak on many topics CCNA tests and still pass the exam. You cannot be weak on subnetting and pass the CCNA. In production, you will be surprised how much subnetting knowledge will help.

Now that we all use private addressing and NAT/PAT we can get lazy and use a /24 just about everywhere with the 10.0.0.0 network. After all, how many of us really need 65,536 networks that handle 254 hosts? However, if I am using registered IPv4 address space I must be very careful with my addressing so I don't run out of addresses. For most networks, I use a /25 for Ethernets, /31 for point-to-points, and a /28 or /29 for multipoints. However, the ISPs I've worked with often work with many different masks with their clients. CCNA tries to cover material relevant to all network admins from the smallest SOHO to the largest ISP.

HTH

 

[burtsbees]

Also, you'll find in the real world that 2 bit masks make things much easier for point to point links, like T1's. A properly subnetted network also makes things easier---you can eliminate the possibility of overlapping networks, especially when working with things like site-to-site VPNs.
Subnetting also helps you figure out supernetting---what to summarize and what not to summarize in routing protocols, and summarizing to save time when making acl's and static routes, things like that. Here's an example of the usefullness of VLSM...

http://www.tek-tips.com/viewthread.cfm?qid=1493077&page=1

Of course that person's scenario could also be solved with summarization, but they asked about within the same address space.
HTH

Burt

 

[CiscoGuy33]

bobbyforhire,

LEARN IT !!!!

I had at least 11 questions that had something to do with subnetting, direct or indirect on one of the CCNA exams I have taken over the years. Cisco must think it is important!!!

I have always tried to explain to my students - the questions that Cisco asks on the CCNA tend to test you in several different areas - both directly and indirectly!

They really make you think!!!!

You would be surprized where you use it in the real world on real networks!!!

Hope this helps!

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

 

[bobbyforhire]

Ok, So. As i stated before I have been hitting the books hard. So far i have found my only weakness is knowing the OSI layers. I know the sequance of the OSI layers APSTNDP.
Does anyone have an learning tips on what all of the layers do.


As for the subnetting....it's FUN..i have found myself trying to setup for 1000 networks on a class A...it's just fun....i love....NETWORKS!

 

[DallasBPF]

i found that using flash cards helped

------------------------------------
Dallas, Texas
Telecommunications Tech
CCVP, CCNA, Net+

CCNP in the works

 

[maczen]

Bobby,
Here is a link that I found useful for the OSI layers..

http://computer.howstuffworks.com/osi.htm

The layers are pretty simple once you have studied them for a while... They are perhaps the best toubleshooting tool available...

You can troubleshoot from the bottom up or start in the middle with a mere ping (Layer 3 test).. If that does not work try a show cdp neighbor command (Layer 2)... Remember that collisions are symbolic of Layer 1 and so are NEXT, FEXT etc. A traceroute command tests your Layer three connectivity while providing insight into the area a problem may be occurring. In other words if you have Layer 1 and 2 but can't ping then follow with a traceroute if multiple routers are involved in the path. A telnet or SSH will test all seven layers as does a web browser or email client etc. Hopefully this will help some with the OSI.

As far as Subnetting goes.. You are on the right path.. Just don't skimp the binary side in search of a shortcut.. I initially tried that path and it will only confuse you in the long run. I found out that subnetting is actually VERY easy. Just remember that you have network bits, subnet bits and host bits... three types and not two. That may or may not make since now but I promise that it will and it makes a world of difference once you actually grasp the concept.. That is when it gets easy!

B Haines
CCNA, FOI

 

[bobbyforhire]

Something else that i have found to be easy for me to remember is the compairing of the OSI to DOD layers

3 on top 2 on the bottom.

The top 3 layers are at the first layer in the DOD. Transfer and Network are in the middle of the dod with there own layers (DOD layers 2 and 3) and the bottom two are just one layer in the dod.. so

3 on top 2 on the bottom

I think i'm going to hit up some flashcards as that seems to be the best bet with the way my brain works.

 

[maczen]

OSI DOD
--------------------------
Application Process
Presentation
Session

Transport Host To Host

Network Internet

Datalink Network Access
Physical

B Haines
CCNA, FOI

 

[lerdalt]

don't forget too:
All People Seem To Need Data Processing

 

[burtsbees]

What about the prostitute one???

Burt

 

[Cluebird]

All Prostitutes Seem To Need Deep Penetration.
Please Do Not Throw Sausage Pizza Away
People Don't Need To See Paula Abdul

Learn it.

 

[bobbyforhire]

LOl, i have got the the order down pat. My issue is determining what they all do.

 

[lerdalt]

Yeah it was tough trying to learn what easy layer does. I always found the lower layers the easiest, the upper ones were always harder keeping track of what goes where.

Flash cards are probably going to be your best bet. I drilled those pages and made lots of sample charts and just kept reviewing it.

 

[SteveTheGeek]

For most networks, I use a /25 for Ethernets, /31 for point-to-points, and a /28 or /29 for multipoints."

Did you mean /30 for point-to-points? My understanding is that a /31 gives you a network address, a broadcast address, and no usable IPs.

 

[burtsbees]

The /31 can only be used on Cisco equipment with an IOS that supports it. Otherwise, you need /30.

Burt

 

[maczen]

I believe that Burt is referring to the "IP SUBNET ZERO" command.. On by default since 12.0..

https://cisco.hosted.jivesoftware.com/message/2462

Basically, you CAN assign your zero subnet addresses giving you another to play with but from what I have read it is not a best practice and a lot of people seem to frown on it.. It works but may confuse others basically...

Is really cool to see someone reference it like that though.. I was not sure until now that it could be used like that.. Been meaning to play with it but I am easily and often distracted.. LoL

Thanks Burt!

B Haines
CCNA, FOI

 

[burtsbees]

No, I was referring to using a /31 for point to point links. This only gives you the network and broadcast addresses, and unless you have the right IOS, it won't let you do it. /30 is the highest you can go, since it gives you 2 USABLE addresses. Again, I have only seen Cisco devices allow the /31.

Burt