Category Archives: CCENT

Are You Smarter Than a CCENT? Transport Layer

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Here is a query from a current project – enjoy!

  1. You are examining a packet capture from your local network. What two determinations can you make from this output? (Choose 2)

100-105a. This is a UDP packet
b. This is a TCP packet
c. The target destination is FTP
d. The target destination is HTTP

Correct Answer: b, d

Explanation: Due to its use of reliable transmissions, Transmission Control Protocol (TCP) uses many fields in its packet structure. These include:

  • source TCP port number
  • destination TCP port number
  • sequence number
  • acknowledgement number
  • TCP data offset
  • reserved data
  • control flags
  • window size
  • TCP checksum
  • urgent pointer
  • TCP optional data

In contrast, the unreliable User Datagram Protocol (UDP) packets feature these simple fields:

  • source port number
  • destination port number
  • length
  • checksum

From the destination TCP port number here of 80, you can determine the intended target service is the Hypertext Transfer Protocol (HTTP). Know the following common ports for this exam:

Port Number TCP or UDP Protocol
20 TCP FTP Data
21 TCP FTP Control
22 TCP SSH
23 TCP Telnet
25 TCP SMTP
53 UDP DNS
67, 68 UDP DHCP
69 UDP TFTP
80 TCP HTTP
110 TCP POP3
161 UDP SNMP
443 TCP SSL/TLS
514 UDP Syslog
520 UDP RIP

ICND1 100-105 NAT Quiz!

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NAT

Good luck with this quiz based on questions from my ICND1 Exam Cram for 100-105!

CCENT 100-105 Configure, Verify, and Troubleshoot Inside Source NAT

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