GATEverse — GATE CSE previous year questions

Consider two hosts $P$ and $Q$ connected through a router $R$ . The maximum transfer unit $\text{(MTU)}$ value of the link between $P$ and $R$ is $1500$ bytes, and between $R$ and $Q$ is $820$ bytes. A $\text{TCP}$ segment of size $1400$ bytes was transferred from $P$ to $Q$ through $R$ , with $\text{IP}$ identification value as $\textsf{0x1234}.$ Assume that the $\text{IP}$ header size is $20$ bytes. Further, the packet is allowed to be fragmented, i.e., $\textsf{Don’t Fragment (DF)}$ flag in the $\text{IP}$ header is $\textit{not}$ set by $P$ . Which of the following statements is/are correct?

(A)

Two fragments are created at $R$ and the $\text{IP}$ datagram size carrying the second fragment is $620$ bytes.

(B)

If the second fragment is lost, $R$ will resend the fragment with the $\text{IP}$ identification value $\textsf{0x1234}.$

(C)

If the second fragment is lost, $P$ is required to resend the whole $\text{TCP}$ segment.

(D)

$\text{TCP}$ destination port can be determined by analysing $\textit{only}$ the second fragment.