218 lines
4.2 KiB
HTML
218 lines
4.2 KiB
HTML
<HTML
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>Protecting your host from SYN floods</TITLE
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NAME="LARTC.COOKBOOK.SYNFLOOD-PROTECT"
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>15.2. Protecting your host from SYN floods</H1
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><P
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>>From Alexey's iproute documentation, adapted to netfilter and with more
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plausible paths. If you use this, take care to adjust the numbers to
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reasonable values for your system.</P
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><P
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>If you want to protect an entire network, skip this script, which is best
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suited for a single host.</P
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><P
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>It appears that you need the very latest version of the iproute2 tools to
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get this to work with 2.4.0.</P
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> <TABLE
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>#! /bin/sh -x
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#
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# sample script on using the ingress capabilities
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# this script shows how one can rate limit incoming SYNs
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# Useful for TCP-SYN attack protection. You can use
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# IPchains to have more powerful additions to the SYN (eg
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# in addition the subnet)
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#
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#path to various utilities;
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#change to reflect yours.
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#
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TC=/sbin/tc
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IP=/sbin/ip
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IPTABLES=/sbin/iptables
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INDEV=eth2
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#
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# tag all incoming SYN packets through $INDEV as mark value 1
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############################################################
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$iptables -A PREROUTING -i $INDEV -t mangle -p tcp --syn \
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-j MARK --set-mark 1
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############################################################
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#
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# install the ingress qdisc on the ingress interface
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############################################################
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$TC qdisc add dev $INDEV handle ffff: ingress
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############################################################
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#
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#
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# SYN packets are 40 bytes (320 bits) so three SYNs equals
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# 960 bits (approximately 1kbit); so we rate limit below
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# the incoming SYNs to 3/sec (not very useful really; but
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#serves to show the point - JHS
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############################################################
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$TC filter add dev $INDEV parent ffff: protocol ip prio 50 handle 1 fw \
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police rate 1kbit burst 40 mtu 9k drop flowid :1
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############################################################
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#
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echo "---- qdisc parameters Ingress ----------"
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$TC qdisc ls dev $INDEV
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echo "---- Class parameters Ingress ----------"
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$TC class ls dev $INDEV
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echo "---- filter parameters Ingress ----------"
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$TC filter ls dev $INDEV parent ffff:
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#deleting the ingress qdisc
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#$TC qdisc del $INDEV ingress</PRE
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> </P
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>Rate limit ICMP to prevent dDoS</TD
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