70-291 Subnetting and subtracting 2 for host and broadcast

[wasisnt]

I was watching a video for the subnetting portion of the 70-291 and they were saying that you don't need to subtract the 2 for all 0s and all 1s when making a custom subnet mask for the network IDs anymore. But you still do for the host IDs.

They say its because of newer routers made since 1995. Does Microsoft feel the same way about this? I would like to know if I should be subtracting 2 or not for the test.

MCSE NT 4.0, MCP (2003), A+ & Network +

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[kmcferrin]

I don't follow your distinction between network and host IDs. As long as I've been using TCP/IP you've always lost the all 1s and all 0s addresses in the subnet range to the broadcast/network numbers and those IPs cannot be used for a host address. In other words, if you want 7 usable addresses you cannot use a /248 (only gives you 6 addresses instead of 8), you must use a /240 (gives you 14 addresses instead of 16).

If you have questions, I highly recommend that you look at something like Solar Winds Subnet Calculator. You can't use it during the test, but you can play around with it and really get a good feel for how it works.

 

[wasisnt]

Yes you lose all 1s and 0s because you cant use them for host IDs. But in the past you would lose the 1s and 0s for network IDs as well. Now this video says you dont have to lose the 1s and 0s for the network IDs but only the host IDs.

Lets say you have an IP address and you need 50 hosts and 4 networks.

So you do your math and get lets say 84 host IDs so you drop the 2 and end up with 82.

Then you do the math for the network side and get lets say 6 network IDs. I remember having to drop the 2 for a total of 4 network IDs. Is that not the case anymore?

MCSE NT 4.0, MCP (2003), A+ & Network +

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[kmcferrin]

Oh. I don't think that you lose them for the network IDs. I haven't seen anything like that before. Based on what you said above, if you need for networks with 50 hosts on each and your starting address was 192.168.0.0 you would get:


Subnet Mask Size Host Range Broadcast
192.168.0.0 255.255.255.192 62 192.168.0.1 to 192.168.0.62 192.168.0.63
192.168.0.64 255.255.255.192 62 192.168.0.65 to 192.168.0.126 192.168.0.127
192.168.0.128 255.255.255.192 62 192.168.0.129 to 192.168.0.190 192.168.0.191
192.168.0.192 255.255.255.192 62 192.168.0.193 to 192.168.0.254 192.168.0.255

 

[wasisnt]

I was just watching an older video by the same company (CBT Nuggets) and this guy was dropping the 2 for the network portion as well as the host.

He was using the typical subnetting formula.

H to the power of 2 minus 2 for hosts (H= host bits)
N to the power of 2 minus 2 for networks (N= network bits)

Ive seen it done with and without subtracting the 2 for the network IDs but was wondering what Microsoft will use for the test.

MCSE NT 4.0, MCP (2003), A+ & Network +

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[wasisnt]

Ooops I mean

2 to the H minus 2 for hosts (H= host bits)
2 to the N minus 2 for networks (N= network bits)

MCSE NT 4.0, MCP (2003), A+ & Network +

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[theravager]

Microsoft exams have been this way since 2003 server. Its know as zero length subnet masking.

Don't worry thou as you will not find any exam questions that have answers that will be affected by this.