CCIE Security Exam: TCP Packet Response | Host SEQ Number 1234 | ACK Number 5678 | Length 1000 Bytes

TCP Packet Response

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If a host receives a TCP packet with an SEQ number of 1234, an ACK number of 5678, and a length of 1000 bytes, what will it send in reply?



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A. B. C. D.


In order to determine the correct answer, we need to understand how the TCP protocol works and how it handles data transfer.

TCP (Transmission Control Protocol) is a connection-oriented protocol that provides reliable, ordered, and error-checked delivery of data between applications. It operates on top of the IP protocol, which provides the basic packet delivery service.

When a TCP connection is established between two hosts, a three-way handshake occurs. During this handshake, the hosts exchange TCP packets with SYN and ACK flags to establish the connection. Once the connection is established, data can be transferred using TCP packets.

Each TCP packet contains a sequence number (SEQ) and an acknowledgment number (ACK). The SEQ number indicates the byte number of the first byte in the packet, and the ACK number indicates the next expected byte number.

In the given scenario, the host receives a TCP packet with a SEQ number of 1234, an ACK number of 5678, and a length of 1000 bytes. This means that the packet contains 1000 bytes of data starting from byte number 1234 and the next expected byte number is 2234 (5678 + 1000).

To reply to this packet, the host needs to send a TCP packet with the ACK flag set and the ACK number set to 2234. The SEQ number should be set to the next byte the host expects to receive, which is 5678.

Therefore, the correct answer is C. a TCP packet with SEQ number: 1234, and ACK number: 2234.