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Special Forums Cybersecurity ~ IPTables : Limit Incoming UDP Packets With a Certain Length ~ Post 302307356 by otheus on Wednesday 15th of April 2009 06:53:39 AM
Old 04-15-2009
I'm not sure, but the second "-m length --length 20" is redundant. You only get to that table if this condition is true. What I'm not clear about the length module is if it is the rule that gets limited or something else. If it's the rule, then this would drop any packet over 20 bytes after there have been 5 per second.

Do you want to limit it by IP address? Then I recommend you use the "recent" feature:

Code:
iptables -N CHECK1
iptables -A INPUT -p udp -m length --length 20 -j CHECK1

iptables -A CHECK1 -m recent --name longudp --rcheck 1 --hitcount 5 -j DROP
iptables -A CHECK1 -m recent --name longudp --set -j RETURN

 

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spray(1M)						  System Administration Commands						 spray(1M)

NAME
spray - spray packets SYNOPSIS
/usr/sbin/spray [-c count] [-d delay] [-l length] [-t nettype] host DESCRIPTION
spray sends a one-way stream of packets to host using RPC, and reports how many were received, as well as the transfer rate. The host argu- ment can be either a name or an Internet address. spray is not useful as a networking benchmark, as it uses unreliable connectionless transports, UDP for example. spray can report a large number of packets dropped when the drops were caused by spray sending packets faster than they can be buffered locally, that is, before the packets get to the network medium. OPTIONS
-c count Specify how many packets to send. The default value of count is the number of packets required to make the total stream size 100000 bytes. -d delay Specify how many microseconds to pause between sending each packet. The default is 0. -l length The length parameter is the numbers of bytes in the Ethernet packet that holds the RPC call message. Since the data is encoded using XDR, and XDR only deals with 32 bit quantities, not all values of length are possible, and spray rounds up to the nearest possible value. When length is greater than 1514, then the RPC call can no longer be encapsulated in one Ether- net packet, so the length field no longer has a simple correspondence to Ethernet packet size. The default value of length is 86 bytes, the size of the RPC and UDP headers. -t nettype Specify class of transports. Defaults to netpath. See rpc(3NSL) for a description of supported classes. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWrcmdc | +-----------------------------+-----------------------------+ SEE ALSO
rpc(3NSL), attributes(5) SunOS 5.10 6 Nov 2000 spray(1M)
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