Am I studying with old books? *confused*

notheory

Hello,

I recently added the Official exam certification library (Wendell Odom) to my collection. It says Third Edition on the Library but after opening it and taking out the books it says Second Edition on both the CCENT/CCNA ICND1 and CCEN/CCNA ICND2 books.

If I browser through Amazon, I can see that there is the Third Edition of both books available. I'm very confused.
Are my books outdated? And why does it say Third Edition on the library hardcover but only Second Edition on the actual books? :

steve2012

Your books are fine for the CCNA.

I have the same set and passed the ICND1 exam recently.
There are a few new updates to the info but overall, there have been no major exam changes to the CCNA exams and you should do fine with those books.

Good luck on your studies!


Steve

jsb515

Second is fine, I think Wendell even says they second editions are good and that the third just has a few updates but nothing that will hurt you on the test.

notheory

Thanks for the clarification guys.

mikespranger

here's a crazy question - i have an odom book for the ccent, from like 2003 or so, and it shows something weird for subnetting -
says to subtract the 2 even when you are doing number of subnets-just like you do for number of hosts.
i tried to ignore it, since it's backwards, but it threw me off

maybe i read it wrong

boredgamelad

That information is a bit outdated thanks to the ip subnet-zero command. Here's an article that might help clarify things for you, mike.

The “ip subnet-zero” Command | PacketU

mikespranger

Thx- just to be sure, on the test it's -2 for # of hosts right?

Xyro

Yes, it's -2 for the number of hosts in each subnet. 1 (the 1st address) is for network address & 1 (the last address) is for broadcast address.

havenlad

Not quite - the 1st address is 99.99% of the time the default gateway

Xyro

I was trying to keep it as simple as I could.

alan2308

havenlad wrote: »

Not quite - the 1st address is 99.99% of the time the default gateway

The default gateway is a host.

havenlad

I see your point but I would say it is an interface as opposed to a host. What the question was regarding was why we -2 from the number of hosts in any subnet.

If we look at 192.168.255.0 /24 for example:

The 1st network address would be 192.168.255.0
The dg would be 192.168.255.1
The broadcast address would be 192.168.255.255
It is the dg and the broadcast address you would leave out, not the network address. This is where the -2 would be relevant.

The answer would always be the first address is the gateway and the last address is the broadcast address

alan2308

The default gateway is often a router or a firewall, there's nothing special about it in comparison to any other host on the network. And the default gateway does not have to be the first address, it can be any address I choose to assign to it.

And what about a network with more than one gateway? For example, I give the computers the router as a default gateway, and I give phones the phone server as a default gateway. Whether or not its a good design, there's nothing stopping me from doing it. I can even have a network with NO default gateway.

And why would you not count 192.168.255.0 in your example? If it's the network number, it can't be assigned to a host. How is it a useable address?

havenlad

Alan I think you are looking way too deep for the question to be honest. Mike - If it's asking number of hosts, use the -2 rule, one for the broadcast address and one for the default gateway. What Alan's saying isn't wrong, but for the purpose of the exam, it's too deep.

ajs1976

I have to agree with Alan.

In the context of the host portion of an IP address, there are three types of addresses. Network, Host, and Broadcast. Network is all zeroes so it is the first address. Broadcast is all ones so it is the last. Everything else is a Host address. A host is anything that plugs into that subnet and needs an IP address: router, server, workstation, printer, etc.

Using 192.168.1.x/24 as an example. It would go from .0 to .255 and have 256 address. .0 is the network and .255 is the broadcast.

I'm not sure where you are getting that 99.99% .1 is the default gateway. Its nice when it is used, but in my experience, it is no where near that high.

havenlad

I am trying to help in "exam world", not "real world".

alan2308

You're completely wrong in both worlds.

boredgamelad

Gotta agree with alan here.

havenlad wrote: »

Alan I think you are looking way too deep for the question to be honest. Mike - If it's asking number of hosts, use the -2 rule, one for the broadcast address and one for the default gateway.

This is, as alan noted, incorrect. The -2 refers to the subnet ID and the broadcast address. It has nothing to do with default gateway (assuming every network has a default gateway is erroneous as well).

havenlad wrote: »

If we look at 192.168.255.0 /24 for example:

The 1st network address would be 192.168.255.0
The dg would be 192.168.255.1
The broadcast address would be 192.168.255.255
It is the dg and the broadcast address you would leave out, not the network address. This is where the -2 would be relevant.

The bolded portion is, again, wrong.

192.168.255.0/24 contains 256 IP addresses (192.168.255.0 through 192.16.255.255)

192.168.255.0 is the subnet ID, and not counted towards the number of usable hosts (-1).
192.168.255.1 is the first usable host.
192.168.255.254 is the last usable host.
192.168.255.255 is the broadcast ID, and not counted towards the number of usable hosts (-1).

It's clear, and correct, to say that the subnet ID and broadcast ID are subtracted from the total number of IP addresses to give you the total number of usable hosts (254). This also jives with the (2^n)-2 rule as (2^8 )-2 = (256)-2 = 254.