Question 40

The destination IP address 145.36.109.70 has first two octets 145.36 and third octet $109 = 01101101_2$. Checking each routing table entry:

• 145.36.0.0/16 (E1): First 16 bits are 145.36 $\implies$ Matches (prefix length 16).
• 145.36.128.0/17 (E2): Third octet of subnet is $128 = \mathbf{1}0000000_2$; 17th bit is 1, whereas for $109 = \mathbf{0}1101101_2$ the 17th bit is 0 $\implies$ Does not match.
• 145.36.64.0/18 (E3): Third octet of subnet is $64 = \mathbf{01}000000_2$; bits 17-18 are 01, which matches bits 17-18 of $109 = \mathbf{01}101101_2$ $\implies$ Matches (prefix length 18).
• 145.36.255.0/24 (E4): Third octet $255 \ne 109$ $\implies$ Does not match.
• Default (E5): Matches with prefix length 0.

By the longest-prefix match rule, the /18 entry wins, forwarding the packet to interface E3.