Copyright © 2003 FhG FOKUS
Copyright © 2005-2009 voice-system.ro
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| Revision $Revision: 6120 $ | $Date: 2009-09-14 21:11:57 +0200 (Mon, 14 Sep 2009) $ |
Table of Contents
List of Examples
The module provides a simple mechanism for DOS protection - DOS based on floods at network level. The module keeps trace of all (or selected ones) IPs of incoming SIP traffic (as source IP) and blocks the ones that exceeded some limit. Works simultaneous for IPv4 and IPv6 addresses.
The module does not implement any actions on blocking - it just simply reports that there is a high traffic from an IP; what to do, is the administator decision (via scripting).
There are 2 ways of using this module (as detecting flood attacks and as taking the right action to limit the impact on the system):
manual - from routing script you can force the check of the source IP of an incoming requests, using "pike_check_req" function. Note that this checking works only for SIP requests and you can decide (based on scripting logic) what source IPs to be monitored and what action to be taken when a flood is detected.
automatic - the module will install internal hooks to catch all incoming requests and replies (even if not well formed from SIP point of view) - more or less the module will monitor all incoming packages (from the network) on the SIP sockets. Each time the source IP of a package needs to be analyse (to see if trusted or not), the module will run a script route - see "check_route" module parameter -, where, based on custom logic, you can decide if that IP needs to be monitored for flooding or not. As action, when flood is detected, the module will automatically drop the packages.
The following modules must be loaded before this module:
No dependencies on other OpenSIPS modules.
Time period used for sampling (or the sampling accuracy ;-) ). The smaller the better, but slower. If you want to detect peeks, use a small one. To limit the access (like total number of requests on a long period of time) to a proxy resource (a gateway for ex), use a bigger value of this parameter.
IMPORTANT: a too small value may lead to performance penalties due timer process overloading.
Default value is 2.
How many requests should be allowed per sampling_time_unit before blocking all the incoming request from that IP. Practically, the blocking limit is between ( let's have x=reqs_density_per_unit) x and 3*x for IPv4 addresses and between x and 8*x for ipv6 addresses.
Default value is 30.
Example 1.2. Set reqs_density_per_unit parameter
...
modparam("pike", "reqs_density_per_unit", 30)
...
For how long the IP address will be kept in memory after the last request from that IP address. It's a sort of timeout value.
Default value is 120.
The name of the script route to be triggers (in automatic way) when a package is received from the network. If you do a "drop" in this route, it will indicate to the module that the source IP of the package does not need to be monitored. Otherwise, the source IP will be automatically monitered.
By defining this parameter, the automatic checking mode is enabled.
Default value is NONE (no auto mode).
Example 1.4. Set check_route parameter
...
modparam("pike", "check_route", "pike")
...
route[pike]{
if (src_ip==111.222.111.222) /*trusted, do not check it*/
drop;
/* all other IPs are checked*/
}
....
Process the source IP of the current request and returns false if the IP was exceeding the blocking limit.
Return codes:
1 (true) - IP is not to be blocked or internal error occured.
-1 (false) - IP is source of flooding, being previously detected
-2 (false) - IP is detected as a new source of flooding - first time detection
This function can be used from REQUEST_ROUTE.
One single tree (for both IPv4 and IPv6) is used. Each node contains a byte, the IP addresses stretching from root to the leafs.
Example 2.1. Tree of IP addresses
/ 193 - 175 - 132 - 164 tree root / \ 142 \ 195 - 37 - 78 - 163 \ 79 - 134
To detect the whole address, step by step, from the root to the leafs, the nodes corresponding to each byte of the ip address are expanded. In order to be expended a node has to be hit for a given number of times (possible by different addresses; in the previous example, the node “37” was expended by the 195.37.78.163 and 195.37.79.134 hits).
For 193.175.132.164 with x= reqs_density_per_unit:
After first req hits -> the “193” node is built.
After x more hits, the “175” node is build; the hits of “193” node are split between itself and its child--both of them gone have x/2.
And so on for node “132” and “164”.
Once “164” build the entire address can be found in the tree. “164” becomes a leaf. After it will be hit as a leaf for x times, it will become “RED” (further request from this address will be blocked).
So, to build and block this address were needed 3*x hits. Now, if reqs start coming from 193.175.132.142, the first 3 bytes are already in the tree (they are shared with the previous address), so I will need only x hits (to build node “142” and to make it “RED”) to make this address also to be blocked. This is the reason for the variable number of hits necessary to block an IP.
The maximum number of hits to turn an address red are (n is the address's number of bytes):
1 (first byte) + x (second byte) + (x / 2) * (n - 2) (for the rest of the bytes) + (n - 1) (to turn the node to red).
So, for IPv4 (n = 4) will be 3x and for IPv6 (n = 16) will be 9x. The minimum number of hits to turn an address red is x.