calculating how many hosts/networks

jason2713

I've read so many different variations on how this should and could be done. I need to know for the exam how they are going to grade this question.

2^n-2 for hosts and networks I've heard is the equation, however, I'm doing ****.com's practice tests and they are saying that only applies to hosts, you can use the 2^n for networks (which I am pretty sure is true)

so if a 26 bit Subnet mask is used which is 255.255.255.192 for a class C nework, then you have 2 bits for the networks, and 6 bits for the hosts

2^n-2 = 2^6-2 = 62 hosts
2^n-2 = 2^2-2 = 2 networks

or is it going to be 4 networks since technically you could use the other 2?

I dont get it, very basic question, however, I'm getting 2 different answers and i know they are going to have both as an option in the multiple choice.

georgemc

Simple answer: Four(4)

kafifi13

2^n is for when you use VLSM

2^n-2 should be used when using the same subnet mask on the entire network.

jason2713

great, glad I got that straightened out. I was getting basic questions wrong. real PITA trying to figure out which questions were right and wrong.

jason2713

kafifi13 wrote:

2^n is for when you use VLSM

2^n-2 should be used when using the same subnet mask on the entire network.

VLSM is only in OSPF, RIP V2, and EIGRP correct? and EIGRP requires all cisco equipment as does IGRP? just getting this straight in my head

I think I have all the switching and routing crap in my head straightened out, I gotta move on to NAT, ACLs, and VLSM...as well as IP address conservation.

I took the test and failed because of the simulation parts were taking me entirely too long. I found that if you read the question and run Show Running Config to compare contrast configs of say 2 routers or switches that are messed up, you can usually get what's different and change it. It took me almost 15 mins to figure this was the easiest way to see the problem.

any other tips? I found this usually worked if it wasn't a subnetting or addressing issue.

Gaztop1

I know this might seem like a dumb way to work out Hosts and Networks but worked for me and i think its pretty clever!

Networks

---

> <

---

Hosts
128 64 32 16 8 4 2 1

Just like you would look at an Octet before you convert it into Binary and i am sure most of us know how to do that. Basically everything in the Direction

---

> will equal the amount of networks you will have and everything <

---

will be the amount of Hosts you need or want.

Obviously the best is 2^(n)-2 and u will always come up right but this is just a quick and easy way to do it ( guideline )