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A router uses the following routing table: Destination Mask Interface 144.16.0.0 255.255.0.0 eth0 144.16.64.0 255.255.224.0 eth1 144.16.68.0 255.255.255.0 eth2 144.16.68.64 255.255.255.224 eth3 A packet bearing an estimation address 144.16.68.117 arrives at the router. On which interface will it be forwarded?

A router uses the following routing table: Destination Mask Interface 144.16.0.0 255.255.0.0 eth0 144.16.64.0 255.255.224.0 eth1 144.16.68.0 255.255.255.0 eth2 144.16.68.64 255.255.255.224 eth3 A packet bearing an estimation address 144.16.68.117 arrives at the router. On which interface will it be forwarded? Correct Answer <span style="text-align: -webkit-center;">eth2</span>

The correct answer is "option 3".

CALCULATION:

To calculate the interface, perform the following steps:

1.Bitwise AND between IP address 144.16.68.117 & subnet mask.

2.Match the output network address with the destination address given corresponding to the subnet mask.  

DESTINATION

 

ADDRESS

(GIVEN)

MASK

BITWISE AND

(ADDRESS & MASK)

144.16.0.0

144.16.68.117

255.255.0.0

144.16.0.0

144.16.64.0

144.16.68.117

255.255.224.0

144.16.64.0

144.16.68.0

144.16.68.117

255.255.255.0

144.16.68.0

144.16.68.64

144.16.68.117

255.255.255.224

144.16.68.96

Option 3:

 

1st Octet

2nd Octet

3rd Octet

4th Octet

144.16.68.117 

10010000

00010000 

01000100

1110101

255.255.255.0 (&)

11111111

11111111

11111111

00000000

Result

10010000 

00010000

01000100

00000000
  144 16 68 0

Hence, the packet with IP address 144.16.68.117 will be forwarded to the interface eth2.

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