Question

4. The Network Layer (a) Consider the following routing table for a certain router implementing CIDR (Classless InterDomain Routing). \begin{tabular}{|l|l|} \hline Subnet & Next hop \\ \hline 202.172.208.0/20 & L1 \\ 202.172.221.0/22 & L2 \\ default & R0 \\ \hline \end{tabular} Suppose two packets, with IP addresses 202.172.221.103 and 297.172.207.87 re- spectively, arrive at the router. Describe how they are handled and routed, showing how you work out your answer. Hint: remember the longest matching prefix rule. In addition, note that the dec- imal 202 is represented in binary (word of 8 bits) as 11001010, 172 as 10101100, 208 as 11010000, 221 as 11011101, 103 as 01100111, 207 as 11001111 and 87 as 01010111. (13 marks)

          4. The Network Layer
(a) Consider the following routing table for a certain router implementing CIDR
(Classless InterDomain Routing).
\begin{tabular}{|l|l|}
\hline
Subnet & Next hop \\
\hline
202.172.208.0/20 & L1 \\
202.172.221.0/22 & L2 \\
default & R0 \\
\hline
\end{tabular}
Suppose two packets, with IP addresses 202.172.221.103 and 297.172.207.87 re-
spectively, arrive at the router. Describe how they are handled and routed,
showing how you work out your answer.
Hint: remember the longest matching prefix rule. In addition, note that the dec-
imal 202 is represented in binary (word of 8 bits) as 11001010, 172 as 10101100,
208 as 11010000, 221 as 11011101, 103 as 01100111, 207 as 11001111 and 87 as
01010111.
(13 marks)

4. The Network Layer
(a) Consider the following routing table for a certain router implementing CIDR
(Classless InterDomain Routing).

Subnet Next hop

202.172.208.0/20 L1

202.172.221.0/22 L2

default R0

Suppose two packets, with IP addresses 202.172.221.103 and 297.172.207.87 re-
spectively, arrive at the router. Describe how they are handled and routed,
showing how you work out your answer.
Hint: remember the longest matching prefix rule. In addition, note that the dec-
imal 202 is represented in binary (word of 8 bits) as 11001010, 172 as 10101100,
208 as 11010000, 221 as 11011101, 103 as 01100111, 207 as 11001111 and 87 as
01010111.
(13 marks)

Added by Irene L.

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