Maximum retransmission attempts

FortiGate

FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.

Article Id 312297

Description

This article describes the maximum retransmission attempts the Fortigate TCP stack will attempt before resetting a TCP connection

Scope

FortiGate.

Solution

In TCP protocol, every stream of data sent to one side requires an ACK packet to be received back.

In case the ACK is not received, the sender will retransmit the same data and if ACK is still not received, it will reset the session by sending an RST packet

In FortiGate, the maximum retransmit attempts before sending an RST is 15. After 15 retransmissions, if there is no ACK packet from the receiver, the connection will be closed.

This can be checked with the following command:

fnsysctl cat /proc/sys/net/ipv4/tcp_retries2
15

993

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Technical Tip: Maximum retransmission attempts

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