CCNA - Subnetting and more Subnetting

Refer to Exhibit

A Network Administrator is adding two new hosts to Switch A.  Which three values could be used for the configuration of these hosts? (Choose Three)



A. Host 1 IP Address 192.168.1.79
B. Host 1 IP Address 192.168.1.64
C. Host 1 Default Gateway 192.168.1.78
D. Host 2 IP Address 192.168.1.128
E. Host 2 Default Gateway 192.168.1.129
F. Host 2 IP Address 192.168.1.190

~~~~~~~~~
My Logic is Workstation A and B are using Vlan's 10 & 20 so that's where will focus on.

Vlan10
fa0/0.10
ip address 192.168.1.78 255.255.255.224

Vlan20
ip address 192.168.1.130 255.255.255.192


fa0/0.10 Subnet break down

IP Address - 192.168.1.78
Subnet       - 255.255.255.224

To figure out the / value you know 255.255.255.0 is a /24.
I would then figure out the last octet.

128  + 64 + 32 + 16 + 8 + 4  2  1
  |       |     
128 +  64 + 32 =224

255.255.255.224 would then be a /27 and you know there is 32 hosts because this is the last octet in your math so you then can do the following chart:

Remember you need to remove a number for the Broadcast address:
1   -  31
32  -  63
64  -  95     192.168.1.78  (78 - 95 is your range) Answer A, C
96  -  127
128 -  159
160 -  191
192 -  223
224 -  255


Now for the fa0/0.20 Subnet break down

IP Address - 192.168.1.130
Subnet       - 255.255.255.192

To figure out the / value you know 255.255.255.0 is a /24.
I would then figure out the last octet.

128  + 64 + 32 + 16 + 8 + 4  2  1
  |        |         
128 +  64 = 192

255.255.255.192 would then be a /26 and you know there is 64 hosts because this is the last octet in your math so you then can do the following chart:


Remember you need to remove a number for the Broadcast address:
1      -  63
64    -  127
128  -  191     192.168.1.130 (128 - 191 is your range) Answer F
192  -  255

A. Host 1 IP Address 192.168.1.79 (In Range)
B. Host 1 IP Address 192.168.1.64 (Not in Range)
C. Host 1 Default Gateway 192.168.1.78 (Vlan10's IP is the Gateway)
D. Host 2 IP Address 192.168.1.128 (Not in Range)
E. Host 2 Default Gateway 192.168.1.129 (Not Vlan 20's IP)
F. Host 2 IP Address 192.168.1.190 (In Range)



Edited by lodogg - 06 December 2007 at 9:02pm