Connection Rate Limiting

Tom Eastep

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Shorewall supports several mechanisms for limiting connection rates. These are described in the following sections.

Rates are expressed in terms of a connections per unit time and a burst. An interval is calculated by dividing the unit of time by the number of connections allowed in that unit of time (connections/{sec|min|hour|day|week|month}[:burst]

Example: 4/min:5

Connections = 4
Unit of time = 1 minute
Interval = 1 minute/4 = 15 seconds.
Burst = 5

As each connection arrives,if the burst count is > 0 the burst count is reduced by one and the connection is accepted. After each interval (15 seconds) that passes without a connection arriving, the burst count is incremented by 1 but is not allowed to exceed its initial setting (5).

By default, the aggregate connection rate is limited. If the specification is preceded by "s:" or "d:", then the rate is limited per SOURCE or per DESTINATION IP address respectively.

Policy Rate Limiting

The LIMIT column in the /etc/shorewall/policy file applies to TCP connections that are subject to the policy. The limiting is applied BEFORE the connection request is passed through the rules generated by entries in /etc/shorewall/rules. Those connections in excess of the limit are logged and dropped.

Rules Rate Limiting

The RATE LIMIT column in the /etc/shorewall/rules file allows limiting of ACCEPT, DNAT and Action rules.

Limit Action

The Limit Action is a legacy mechanism that limits connections per source IP. It does not support the notion of a burst size.


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