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Conntrack / Netfilter

The settings on this page allow you to control some advanced network parameters. In most cases, the default settings are already fine. You should 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. In general, conntrack can be used to search, list, inspect and maintain the Linux kernel's connection tracking subsystem.

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 not being designed to work well 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 often shows that the SIP helper often makes VoIP work worse, not better.


TCP/UDP Buffers: This settings defines the amount of TCP/UDP buffers allowed (again, to and from the router). Please be aware that this setting needs to be tweaked carefully. A large buffer will facilitate higher throughput, but a buffer too big might create a collateral 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 L7 matching for inbound traffic, caches the results, and marks the traffic as outbound.

advanced-ctnf.txt · Last modified: 2022/01/11 16:00 by hogwild