Subnetting Tricks and Tips with concepts.

Question and Answer regarding Subnetting concepts.

Q.1 – What is the maximum number of IP addresses that can be assigned to hosts on a local subnet that uses the 255.255.255.224 subnet mask?

Ans. Remember

/24 ,1 subnet of host 256-2=254

/25  ,2 subnet of host 128-2=126 each valid                                                     128*2=256

/26  ,4 subnet of host 64-2=62 each valid                                                          64*4=256

/27  ,8 subnet of host 32-2=30 each valid                                                          32*8=256

/28  ,16 subnet of host 16-2=14 each valid                                                          16*16=256

/29  ,32 subnet of host 8-2=6 each valid                                                               8*32=256

/30  ,64 subnet of host 4-2=2 each valid                                                              4*64=256

/31  ,128 subnet of host 2 each(there is no network and broadcast)            2*128=256

/32  ,single ip address(used in cloud for website hosting like)

 

/27 (255.255.255.224) is 3 bits on and 5 bits off. This provides 8 subnets, each with 30 hosts.

 

Q.2 – If a host on a network has the address 172.16.45.14/30, what is the subnetwork this host belongs to?

A. 172.16.45.4

B. 172.16.45.12

C. 172.16.45.0

D. 172.16.45.8

Ans. B.

/30  ,64 subnet of host 4-2=2 each valid                       4*64=256

block size(host in each subnet) of 4 and our subnets are 0, 4, 8, 12, 16, etc. Address 14 is obviously in the 12 subnet.

 

Q.3 – What is the subnetwork address for a host with the IP address 200.10.5.68/28?

A.  200.10.5.0

B.  200.10.5.32

C.  200.10.5.56

D.  200.10.5.64

Ans. D

/28  ,16 subnet of host 16-2=14 each valid        16*16=256

block size is 16 in the fourth octet. 0, 16, 32, 48, 64, 80, etc. The host is in the 64 subnet.

 

Q.4 – You have an interface on a router with the IP address of 192.168.192.10/29. Including the router interface, how many hosts can have IP addresses on the LAN attached to the router interface?

A. 6                              B. 8                                 C. 30                         D. 32

Ans. A

/29  ,32 subnet of host 8-2=6 each valid

So 6 is the answer.