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Conntrack / Netfilter

The settings in this menu allow you to control some advanced network parameters. In most cases, the default settings are fine. Think very carefully before changing the settings from their defaults. You are advised to change these settings only if you have advanced networking knowledge and/or experience.


The Connections menu contains some limited conntrack configuration settings. Conntrack is a Linux utility that provides an interface to the netfilter connection tracking system. It tracks connections, and is used to know how the packets that pass through the system are related to their connections.

In general, conntrack can be used to search, list, inspect and maintain the Linux kernel's connection tracking. Conntrack does NOT manipulate packets, and works independently of NAT functions.

Maximum Connections: Defines the maximum number of sessions handled by the router (/proc/sys/net/ipv4/netfilter/ip_conntrack_max).

Clicking on the [ Count current … ] link gives you a real-time view of the current demand for oconnections.

Hash Table Size: This parameter allows you to tweak the following kernel attribute: /proc/sys/net/ipv4/netfilter/ip_conntrack_buckets

TCP Timeout

The TCP Timeout table allows you to define some critical TCP parameters, such as timeouts. These affect only connections towards the router and not through the router.

UDP Timeout

The UDP Timeout table defines the timeouts of UDP packets to and from the router.

Other Timeouts

Other Timeouts allows further adjustments to the router's timeout settings.

Tracking/NAT Helpers

Some protocols are well-known for being poorly designed to work with NAT. Some workarounds (Helpers) have been developed to allow these protocols to operate in a NAT environment. Enabling the option will enable the helper procedure.

Be advised that on networks where VoIP is in use, the use of the SIP helper is not recommended. While this may seem counterintuitive, real world experience shows that the SIP Helper often makes VoIP function work worse, not better.


TCP/UDP Buffers: This setting defines the amount of TCP/UDP buffers allowed (to and from the router). This setting needs to be tweaked carefully. A large buffer will facilitate higher throughput, but too large a buffer might create bufferbloat. Bloated buffers lead to network-crippling latency spikes.

TTL Adjust: This option increases or decreases the packet Time-To-Live value crossing the router.

Inbound Layer 7: This enables Layer 7 matching for inbound traffic, caches the results, and marks the traffic as outbound.

advanced-ctnf.txt · Last modified: 2023/05/24 22:02 by hogwild