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210-255 · Question #76

Refer to the following packet capture. Which of the following statements is true about this packet capture? 00:00:04.549138 IP omar.cisco.com.34548 > 93.184.216.34.telnet: Flags [S], seq 3152949738, w

The correct answer is C. This is a Telnet transaction that is timing out and the server is not responding.. The packet capture shows repeated TCP SYN packets from omar.cisco.com to a Telnet port on 93.184.216.34 with no SYN-ACK responses, indicating a connection that is timing out.

Network Intrusion Analysis

Question

Refer to the following packet capture. Which of the following statements is true about this packet capture? 00:00:04.549138 IP omar.cisco.com.34548 > 93.184.216.34.telnet:

Flags [S], seq 3152949738, win 29200, options [mss 1460,sackOK,TS val 1193148797 ecr 0,nop,wscale 7], length 0 00:00:05.547084 IP omar.cisco.com.34548 > 93.184.216.34.telnet: Flags [S], seq 3152949738, win 29200, options [mss 1460,sackOK,TS val 1193149047 ecr 0,nop,wscale 7], length 0 00:00:07.551078 IP omar.cisco.com.34548 > 93.184.216.34.telnet: Flags [S], seq 3152949738, win 29200, options [mss 1460,sackOK,TS val 1193149548 ecr 0,nop,wscale 7], length 0 00:00:11.559081 IP omar.cisco.com.34548 > 93.184.216.34.telnet: Flags [S], seq 3152949738, win 29200, options [mss 1460,sackOK,TS val 1193150550 ecr 0,nop,wscale 7], length 0

Options

  • AThe host with the IP address 93.184.216.34 is the source.
  • BThe host omar.cisco.com is the destination.
  • CThis is a Telnet transaction that is timing out and the server is not responding.
  • DThe server omar.cisco.com is responding to 93.184.216.34 with four data packets.

How the community answered

(19 responses)
  • A
    5% (1)
  • B
    11% (2)
  • C
    79% (15)
  • D
    5% (1)

Why each option

The packet capture shows repeated TCP SYN packets from omar.cisco.com to a Telnet port on 93.184.216.34 with no SYN-ACK responses, indicating a connection that is timing out.

AThe host with the IP address 93.184.216.34 is the source.

In each capture line, 93.184.216.34 appears after the '>' symbol, which designates it as the destination, not the source.

BThe host omar.cisco.com is the destination.

omar.cisco.com appears before the '>' symbol in every line, identifying it as the source host, not the destination.

CThis is a Telnet transaction that is timing out and the server is not responding.Correct

All four packets show only the SYN flag set from omar.cisco.com with the same sequence number, meaning no SYN-ACK was ever received from the server. The retransmission intervals approximately double each time (1s, 2s, 4s), matching TCP exponential backoff behavior during a timeout. This pattern confirms the Telnet server at 93.184.216.34 is not responding to the connection attempts.

DThe server omar.cisco.com is responding to 93.184.216.34 with four data packets.

omar.cisco.com is the client sending SYN connection-request packets, not a server sending data; additionally, no data packets are present since only the SYN flag is set throughout the capture.

Concept tested: TCP SYN retransmission and connection timeout identification

Source: https://www.cisco.com/c/en/us/support/docs/ip/transmission-control-protocol-tcp/5215-retransmit.html

Topics

#packet capture analysis#Telnet#TCP SYN#connection timeout

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