In this post, I would like to share a .PCAP file of a TACACS+ TCP stream. This file was captured in a lab environment and is for educational purposes only.

TACACS+ communication is encrypted by default so I have included the TACACS+ key so that you can see the decrypted information.

Download link: https://blog.synack.co.uk/download/pcap-tacacs-pcap-file/

Key: Cisco123

Let me explain a little about the capture…

  1. We can see the initial TCP 3-way handshake occurs from a source of with a destination port of 49 (TACACS+). The device starts by sending an SYN request to

  2. Device responds with a source port of 49 to destination with a TCP SYN-ACK

  3. receives the SYN-ACK and responds with an ACK

  1. After the TCP 3-way handshake has finished, device sends a TACACS+ authentication request. At this stage, you can use the key to decrypted and analyse the TACACS+ communication. We can see that a user: synack has sent a login authentication request to

  2. Device sends an acknowledgement and then sends a TACACS+ packet back to Once this TACACS+ message is decrypted we can see that the TACACS+ server has now asked for a password for user: synack.

  3. Device sends an acknowledgement to say that is has received the request for the password.

  4. Device then sends the password: Password1 back to the TACACS+ server

  5. The TACACS+ server responds with an authentication passed. This means that the user: synack has now been authenticated

  6. The TCP session is now torn down with the device sending a FIN-ACK

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