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How to Avoid PAWS Packet Loss

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Last updated: 2025-11-13 17:38:37

Background

The tcp_tw_recycle parameter is used to quickly reclaim connections in the TIME-WAIT status. However, under certain circumstances, this parameter may cause Protection Against Wrapped Sequence Numbers (PAWS) packet loss issues, especially when network address translation (NAT) exists in the network linkage. Therefore, it is generally recommended to disable the parameter.
Below are the steps to disable tcp_tw_recycle and configure tcp_tw_bucket.

Operation Steps

Disabling tcp_tw_recycle

Temporary Disabling

sudo sysctl -w net.ipv4.tcp_tw_recycle=0

Permanent Disabling

1. Edit the /etc/sysctl.conf file to add or modify the following line:
net.ipv4.tcp_tw_recycle = 0
2. Make the configuration take effect:
sudo sysctl -p

Configuring tcp_tw_bucket

The tcp_tw_bucket parameter is used to set the number of buckets for connections in the TIME-WAIT status. Increasing this value helps the system more efficiently handle a large number of connections in the TIME-WAIT status.

Temporary Configurations

sudo sysctl -w net.ipv4.tcp_max_tw_buckets=4096

Permanent Configurations

1. Edit the /etc/sysctl.conf file to add or modify the following line:
net.ipv4.tcp_max_tw_buckets = 4096
2. Make the configuration take effect:
sudo sysctl -p

Other Related Optimizations

In addition to the two parameters mentioned above, other kernel parameters can also help optimize TCP connection handling:

Increasing the File Descriptor Length Limitation

sudo sysctl -w fs.file-max=100000

Increasing the Number of Open Files Allowed by the System

Edit the /etc/security/limits.conf file to add or modify the following lines:
* soft nofile 65535
* hard nofile 65535

Increasing the Maximum Number of Connections That Can Be Established by the System

sudo sysctl -w net.core.somaxconn=65535

Increasing the Length of Half-Open Connection Queues

sudo sysctl -w net.ipv4.tcp_max_syn_backlog=65535

Reducing the Timeout Duration of the TIME-WAIT Status

sudo sysctl -w net.ipv4.tcp_fin_timeout=15

Verifying the Configuration

You can use the following commands to verify whether the configuration takes effect:
sysctl -a | grep tcp_tw
sysctl -a | grep file-max
sysctl -a | grep somaxconn
sysctl -a | grep tcp_max_syn_backlog
sysctl -a | grep tcp_fin_timeout

Restarting the Service

If you are optimizing a certain service (such as a web server or database), it is recommended to restart the service to ensure that the new kernel parameters take effect.
Previous Topic: Adding Kernel Parameters via GRUB on Linux InstancesNext Topic: History

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