# A few subnetting question

• posted

I am working through subnetting question and I had two that I was not sure about:

1) a firm is assigned the network part 128.171. It selects an 8-bit subnet part. Represent the second host on the third subnet in dotted decimal notation.

I came up with 128.171.4.2

2) You have a 20-bit network part and a 4-bit subnet part, how many hosts can you have per subnet? a. 14 b. 16 c. 254 d. 256 e. none of the above

I came up with C

Thanks

• posted

I personally would go would E, your bits only add up to 24 bits, and their is 32 bits in an IP address....

• posted

The way I figured the second problem was if you had 20 bits for the network and 4 bits for the subnet you have 8 bits left for the hosts.

20+4+8=32

8 bits = 256 hosts - 2 for broadcast and network = 254.

I am lost on the first question, it seems that you would need a subnet mask to answer this question.

Thanks for look> I am working throughsubnettingquestionand I had two that I was not sure > about:

• posted

Let me take a stab at question 1.

128.171.x.x is a class B address, therefore the eight bit subnet will be in the third octet.

So the counting the subnets up I get :-

128.171.0.0 This is the zero subnet not normally acknowledged or required on the CCNA unless specifically asked for so I discount it (please can someone correct me if this wrong!). 128.171.1.0 First subnet 128.171.2.0 Second subnet 128.171.3.0 Third subnet

So I get 128.171.3.2 as the second host on the third subnet.

As for question 2 I think this is more simple. It's a trick question. There can't be a 20 bit network part for the address.

A = 8 network bits. B = 16 network bits C = 24 network bits.

I would therefore have to go with e for this question.

K.

1) a firm is assigned the network part 128.171. It selects an 8-bit subnet part. Represent the second host on the third subnet in dotted decimal notation.

I came up with 128.171.4.2

2) You have a 20-bit network part and a 4-bit subnet part, how many hosts can you have per subnet? a. 14 b. 16 c. 254 d. 256 e. none of the above

I came up with C

Thanks

• posted

The recommendation in the CCNA Cisco Press exam guide (Appendix D p592) is:

If there is no hint in the question use 2^n-2

If the Q includes the words 'classful' 'RIPv1' or is not using VLSM -> 2^n-2

If the Q includes the words 'classless' 'OSPF' 'EIGRP' 'RIPv2' or uses VLSM ->

2^n

The question may explicitly say which to use, or simply infer it.

Cisco themselves give no direct recommendation.

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