Networking homework help

So, I’ve been given a list of IP addresses, and I have to determine whether or not each is a host, network, or broadcast address. The problem is, the text book has yet to explain how to make such a determination.

How do you determine whether or not a given IP address is a broadcast address, a network address, or a host address?

The IP addresses in question.
123.45.67.89
192.168.88.0
10.0.0.255
172.64.12.9
200.34.12.255
47.19.0.0
150.3.0.0
200.100.50.0

Not asking anyone to give me the answers, just asking if someone can take one of the above addresses and show me how to determine the answer.

Last octet in the IP address dictates the determination. Take a guess at which two numbers at the end of the octet aren't normally assigned to networking devices other than routers.

1 Like

Without much explanation.

the first and last addresses are un-usable as they are reserved for the network and broadcast address.

so and address ending in .0 is generally a network address and .255 is broadcast address

BUT!!!!!!! (have i made this noticeable)?

without the subnet masks for each IP theres no way of knowing whats a network, broadcast and host address.

If you assume the subnet for all of them are /24 (255.255.255.0) then its easy. the last number in each will be .0 (network), .255 (broadcast), everything else host. But if its not it could potentially be anything.

For example. if we use 10.0.0.255

if its a /24 then you get
network: 10.0.0.0
broadcast: 10.0.0.255
hosts 10.0.0.1 - 10.0.0.254

if its a /8 you get
network: 10.0.0.0
broadcast: 10.255.255.255
host 10.0.0.1 - 10.255.255.254

edit: so in one case 10.0.0.255 is the broadcast and in the other 10.0.0.255 is a host address

edit2: i made a mistake /25 should have been /24 (fixed it)

2 Likes

Did you mistake /25 for /24?

It's like 8.16.24.32, right?

/25 would be 255.255.255.128

2 Likes

Thanks, no idea what i was thinking, that would change the results :p

1 Like

Oh dammit, same here.

It wasn't me who was supposed to be captain obvious >_>

1 Like

Thanks for all the great info guys. What's confusing the hell of out me is the lack of a subnet mask, as well as Cisco saying that it's now possibly to use .0 and .255 as host addresses.e2

I swear, it's like teachers today are supposed to make the assignment deliberately infuriating, ran than informative.

Networking is infuriating, that's the point. ;)

I mean, in my experience as a consumer, you plug shit in and it works. I get that it's more complicated than that in the real world, but still, to this extent? Seems to me that someone needs to make a program to do this shit automatically.

Thats because consumer devices use a default network almost always 192.168.0.0/24 and youll have a couple of devices on it and itll assign IPs using DHCP.

When you have large networks you cant just assign a single /24

IPv6 is a lot better for autoconfiguration, it still requires setup otherwise how do you define and isolate networks.

no subnet masks????

If by subnet mask, you mean a /24, which our textbook refers to only as a prefix.

Really.. it doesnt tell you what /24 is?

The /24 for example, is part of CIDR (and yes, it defines the subnet mask)

To give a bit of background years ago IP addresses used classful networks, where you might have learned about Class A, B, C, D, E networks (more info)

That sucks, becuase it limits the amount of networks you can have and wastes IP addresses. So they made CIDR Classless Inter Domain Routing (or VLSM) (more info).

This allows you to specify very specific network ranges giving you only the number of hosts you need the /number notation is the CIDR notation for defining subnet masks.

e.x. 10.0.0.0/24 being the same as saying 10.0.0.0 subnetmask 255.255.255.0

hope thats useful

It is. They just.....they aren't coherent in the way they explain things. They will be in the middle of a sentence, and then make some pointless comment about something else that we haven't learned yet, and aren't going to learn for a week or two, and then get back to explaining what they were originally explaining.

Not to mention using different terminology than everyone else apparently uses. I'm still not quite sure what they mean with the term "Subnet ID"....is that the subnet mask (255.255.255.0)? is the the /24? What?.... I just.....GAAH brain explodes.

hm, if there asking whats the subnet id. They probably want the network and subnet. e.g. 192.168.0.0/24 or network 192.169.0.0 subnet mask 255.255.255.0

for example the 'network id' of say 10.10.10.5/24 would be 10.10.10.0/24 or 10.10.10.0 255.255.255.0

edit: feel free to keep asking questions :D

I asked the instructor, and according to her (and her job credentials are extensive and impressive), what she calls the Subnet ID, is the actual IP address (or starts with it). Or what other people could simply call, the Network ID.

I did ask her how you take a given IP (in the case of our project, 30.30.30.0), then take the given possible range of IP addresses (minus 30.30.30.1 and 30.30.30.255) and then pick subnets from that, so that you would end up with the following subnet ID's from that range,

30.30.30.00
30.30.30.64
30.30.30.128
30.30.30.192

This apparently using a relatively (to my knowledge) new routing command that allows the "zero" address (30.30.30.0) to be used as an actual host address, whereas before it would be reserved as the network address.

Please note, my math may be a bit off because of my terrible math skills, being drunk, and complete lack of experience.

Yeah, when you subnetted a class C for example would wouldn't be able to use the first subnet and last subnet. Now you can, relatively new would be 10 years ago :p

You still cant use the first and last addresses in each subnet though as they are all ready allocated for use (network and broadcast address).

Its worth mentioning that a network ID on with own with no other information isn't super useful. 30.30.30.0 doesnt say anything except a network starts there.. where does it end? The only way you can know that is because your given another 4 network IDs so you can figure out its actually 30.30.30.0/26

But even that is assuming that you have been provided every network ID on the network. Which i suppose is an ok assumption in your last example.

I'd recommend watching some of Anthony Sequeira's videos - stormwind live or CBT nuggets on youtube. Or even Dan's Courses.
You'll get a grasp of network fundamentals pretty quick.

I've not watched it but just bookmarked it to looked thought to brush up, this CCNA based series may be useful https://www.youtube.com/playlist?list=PLmdYg02XJt6QRQfYjyQcMPfS3mrSnFbRC