TCP handshakes are integral to the establishment of connections in network communications. Most network engineers are well-acquainted with the traditional 3-way handshake, but the waters get murkier when delving into the lesser-known territories of split handshakes and simultaneous opens. This article sheds light on these handshake variants and their implications on network security, mainly focusing on the proficiency of Palo Alto Networks’ next-gen firewalls in managing them.
The Standard 3-Way Handshake
The 3-way handshake is the cornerstone of TCP connections, facilitating the initiation of a session between a client and a server. The process is as follows:
1. SYN: The client initiates the communication by sending a packet with the SYN (synchronize) flag set to the server.
2. SYN/ACK: In response, the server sends back a packet flagged with SYN and ACK (acknowledgment).
3. ACK: To conclude the handshake, the client acknowledges the receipt of the SYN/ACK packet by sending an ACK packet back to the server.
A --> B: SYN A <-- B: SYN/ACK A --> B: ACK
Step 1: Client A sends a SYNchronize packet to Server B.
Step 2: Server B responds with a SYNchronize-ACKnowledgement packet.
Step 3: Client A sends an ACKnowledgement packet to complete the handshake.
Exploring Variants: Split Handshake and Simultaneous Open
While the 3-way handshake is a standard method for establishing TCP connections, the TCP protocol specifications recognize several other valid handshake methods. These include:
1. 4-Way Split Handshake: This variant involves a different sequence of packets than the traditional handshake, with SYN and ACK packets sent separately. The procedure can manifest in multiple forms, potentially perplexing some network security appliances.
A --> B: SYN A <-- B: ACK A <-- B: SYN A --> B: ACK
Step 1: Client A sends a SYNchronize packet to Server B.
Step 2: Server B responds with an ACKnowledgement packet.
Step 3: Server B sends a SYNchronize packet to Client A.
Step 4: Client A sends an ACKnowledgement packet.
Variation 2:
A --> B: SYN A <-- B: SYN A --> B: SYN/ACK A <-- B: ACK
Step 1: Client A sends a SYNchronize packet to Server B.
Step 2: Server B responds with a SYNchronize packet.
Step 3: Client A sends a SYNchronize-ACKnowledgement packet.
Step 4: Server B sends an ACKnowledgement packet.
2. Simultaneous Open: In this scenario, the client and the server dispatch SYN packets simultaneously. They then respond with SYN/ACK packets, acknowledging each other’s initial SYN packets.
A --> B: SYN A <-- B: SYN A --> B: SYN/ACK A <-- B: SYN/ACK
Step 1: Client A and Server B send SYNchronize packets simultaneously.
Step 2: Both Client A and Server B respond with SYNchronize-ACKnowledgement packets.
3. 5-Way Split Handshake: An extension of the 4-way split handshake, this variant incorporates an additional step, increasing the handshake to five steps and, in turn, potentially confusing specific network security devices.
A --> B: SYN A <-- B: ACK A <-- B: SYN A --> B: SYN/ACK A <-- B: ACK
Step 1: Client A sends a SYNchronize packet to Server B.
Step 2: Server B responds with an ACKnowledgement packet.
Step 3: Server B sends a SYNchronize packet to Client A.
Step 4: Client A sends a SYNchronize-ACKnowledgement packet.
Step 5: Server B sends an ACKnowledgement packet.
Navigating Handshake Complexities with Palo Alto Networks
Addressing the challenges posed by these handshake variations, Palo Alto Networks’ next-gen firewall emerges as a resilient solution. It accurately processes these unconventional handshakes and offers advanced features for enhanced network security. One such feature is the ability to drop TCP Split Handshake in the zone protection profile, preventing the completion of handshakes through the 4 or 5-way methods.
Conclusion
While the 3-way handshake remains a foundational concept in network communications, understanding the intricacies of its lesser-known counterparts is essential for robust network security. Palo Alto Networks’ next-gen firewall exemplifies adaptability in handling diverse handshake types, ensuring secure and seamless connections in an ever-evolving digital landscape.