Subnetting question

Question in the MS Press book, page 2-44. I know I should I've been able to answer this myself, but it's been a year and a few months since my CCNA

. So here goes:

You have a 192.168.64.0/23 address block that you need to subnet as 192.168.64.0/25. The answer on the same page lists 4 subnets, 192.168.64.0, 192.168.64.128, 192.168.65.0, 192.168.65.128. I know where the first 2 came from, but how did the last 2 appear in the answer.

I am definitely missing something here, could someone please help.

Edit: I'll add three more questions here.

1. We can use the calculator during the test, right?
2. Can there be VLSM questions on the test? Transcender has a huge (really huge) question on VLSM.
3. How extensively can RIP and OSPF be on the test. The questions at the back of the MS Press are fairly in-depth, the CCNA stuff.

I hope asking these questions is not in violation of the test DNA, sorry NDA. I just want a general idea.

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flares2

Remember your splitting one network into multiple subnets. Your 192.168.64.0/23 network has a range of 192.168.64.1-192.168.65.255. So, you can split this into 4 /25 subnets.
It looks like you're seeing the /25 subnets as Class C. Remember your network is /23, which is class B.

meadIT

MobilOne wrote:

1. We can use the calculator during the test, right?
2. Can there be VLSM questions on the test? Transcender has a huge (really huge) question on VLSM.
3. How extensively can RIP and OSPF be on the test. The questions at the back of the MS Press are fairly in-depth, the CCNA stuff.

I hope asking these questions is not in violation of the test DNA, sorry NDA. I just want a general idea.

1. Yes, but they are not scientific calculators, just the basic functions (add, subtract, multiply, divide)..no binary conversions.

2. Yes, definately.

3. I don't remember if I had any RIP or OSPF on my exam, so I'll leave this up to someone else.

Essendon

flares2 wrote:

So, you can split this into 4 /25 subnets.

Can I ask how?

dynamik

I'll give you a hint

Starting Network Mask: 11111111.11111111.11111110.00000000
Available Subnet Bits: 11111111.11111111.11111110.00000000

meadIT

You have a 192.168.64.0/23 address block that you need to subnet as 192.168.64.0/25. The answer on the same page lists 4 subnets, 192.168.64.0, 192.168.64.128, 192.168.65.0, 192.168.65.128. I know where the first 2 came from, but how did the last 2 appear in the answer.

Ok, let's break the 3rd and 4th octet into binary. The network portion is in blue.

192.168.64.0/23 = 192.168.01000000.00000000

If you want to subnet it into /25, then you will borrow 2 bits for the subnet (subnet portion in bold).

192.168.64.0/25 = 192.168.01000000.00000000

So our possible subnets could be 00, 01, 10, 11, so that gives us the network addresses

192.168.01000000.00000000 = 192.168.64.0
192.168.01000000.10000000 = 192.168.64.128
192.168.01000001.00000000 = 192.168.65.0
192.168.01000001.10000000 = 192.168.65.128

Essendon

XtreemeChaos wrote:

You have a 192.168.64.0/23 address block that you need to subnet as 192.168.64.0/25. The answer on the same page lists 4 subnets, 192.168.64.0, 192.168.64.128, 192.168.65.0, 192.168.65.128. I know where the first 2 came from, but how did the last 2 appear in the answer.

Ok, let's break the 3rd and 4th octet into binary. The network portion is in blue.

192.168.64.0/23 = 192.168.01000000.00000000

If you want to subnet it into /25, then you will borrow 2 bits for the subnet (subnet portion in bold).

192.168.64.0/25 = 192.168.01000000.00000000

So our possible subnets could be 00, 01, 10, 11, so that gives us the network addresses

192.168.01000000.00000000 = 192.168.64.0
192.168.01000000.10000000 = 192.168.64.128
192.168.01000001.00000000 = 192.168.65.0
192.168.01000001.10000000 = 192.168.65.128

Thank you, that's cleared the mystery up

the_erickee

XtreemeChaos wrote:

You have a 192.168.64.0/23 address block that you need to subnet as 192.168.64.0/25. The answer on the same page lists 4 subnets, 192.168.64.0, 192.168.64.128, 192.168.65.0, 192.168.65.128. I know where the first 2 came from, but how did the last 2 appear in the answer.

Ok, let's break the 3rd and 4th octet into binary. The network portion is in blue.

192.168.64.0/23 = 192.168.01000000.00000000

If you want to subnet it into /25, then you will borrow 2 bits for the subnet (subnet portion in bold).

192.168.64.0/25 = 192.168.01000000.00000000

So our possible subnets could be 00, 01, 10, 11, so that gives us the network addresses

192.168.01000000.00000000 = 192.168.64.0
192.168.01000000.10000000 = 192.168.64.128
192.168.01000001.00000000 = 192.168.65.0
192.168.01000001.10000000 = 192.168.65.128

Great explaination!!!

Psoasman

There is a good chance you will be tested on these. I would know how to set these up, when you would use them. OSPF is harder to set up, but is dynamic and easier to maintain once set up and is used by larger companies.
RIP is still used in smaller companies. IT is easier to set up, but harder to maintain. There is a 15-hop limit with RIP v1.
RIP v1has been around since the late 60's when the goverment started the internet aka ARPANET....not AL GORE!!

I think I only had a couple of questions on this. Main focus was DNS