Ip addressing.

Question

Destination	Subnet Mask	Interface
128.75.43.0	255.255.255.0	Eth 0
128.75.43.0	255.255.255.128	Eth 1
144.16.68.0	255.255.255.0	Eth 2
144.16.68.64	255.255.255.224	Eth 3

On which interfaces will the router forward packets addressed to destinations 128.75.43.16 and 144.16.68.117 ?

a. Eth0 and Eth3

b. Eth1 and Eth3

c. Eth0 and Eth2

d. Eth1 and Eth2

Answer 1

first Ip-128.75.43.16

subnet mask given as 255.255.255.0 and 255.255.255.128

=>(128.75.43.16 )&(255.255.255.0)=128.75.43.0

=>(128.75.43.16 )&(255.255.255.128)=>128.75.43.0

here we are getting two net id with different subnet mask so take that one which has greater subnet mask(means more number of 1's)=>Eth 1

---

second ip-144.16.68.117

subnet mask given as 255.255.255.0 and 255.255.255.224

=>(144.16.68.117)&(255.255.255.0)=144.16.68.0(matches with Eth 2)

=>(144.16.68.117)&(255.255.255.224)=144.16.68.96(not matches)

hence this implies Eth 2

so option (d) is correct.