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16.3. Usage
16.3.1. Check for support
Load module, if so compiled
# modprobe ip6_tables |
Check for capability
# [ ! -f /proc/net/ip6_tables_names ] && echo "Current kernel doesn't support ¬ 'ip6tables' firewalling (IPv6)!" |
16.3.2. Learn how to use ip6tables
16.3.2.1. List all IPv6 netfilter entries
Short
# ip6tables -L
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Extended
# ip6tables -n -v --line-numbers -L
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16.3.2.3. Insert a log rule at the input filter with options
# ip6tables --table filter --append INPUT -j LOG --log-prefix "INPUT:"
¬ --log-level 7
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16.3.2.6. Allow ICMPv6
Using older kernels (unpatched kernel 2.4.5 and iptables-1.2.2) no type can be specified
Accept incoming ICMPv6 through tunnels
# ip6tables -A INPUT -i sit+ -p icmpv6 -j ACCEPT
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Allow outgoing ICMPv6 through tunnels
# ip6tables -A OUTPUT -o sit+ -p icmpv6 -j ACCEPT
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Newer kernels allow specifying of ICMPv6 types:
# ip6tables -A INPUT -p icmpv6 --icmpv6-type echo-request -j ACCEPT
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16.3.2.7. Rate-limiting
Because it can happen (author already saw it to times) that an ICMPv6 storm will raise up, you should use available rate limiting for at least ICMPv6 ruleset. In addition logging rules should also get rate limiting to prevent DoS attacks against syslog and storage of log file partition. An example for a rate limited ICMPv6 looks like:
# ip6tables -A INPUT --protocol icmpv6 --icmpv6-type echo-request
¬ -j ACCEPT --match limit --limit 30/minute
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16.3.2.8. Allow incoming SSH
Here an example is shown for a ruleset which allows incoming SSH connection from a specified IPv6 address
Allow incoming SSH from 3ffe:ffff:100::1/128
# ip6tables -A INPUT -i sit+ -p tcp -s 3ffe:ffff:100::1/128 --sport 512:65535
¬ --dport 22 -j ACCEPT
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Allow response packets (at the moment IPv6 connection tracking isn't in mainstream netfilter6 implemented)
# ip6tables -A OUTPUT -o sit+ -p tcp -d 3ffe:ffff:100::1/128 --dport 512:65535
¬ --sport 22 ! --syn j ACCEPT
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16.3.2.9. Enable tunneled IPv6-in-IPv4
To accept tunneled IPv6-in-IPv4 packets, you have to insert rules in your IPv4 firewall setup relating to such packets, for example
Accept incoming IPv6-in-IPv4 on interface ppp0
# iptables -A INPUT -i ppp0 -p ipv6 -j ACCEPT
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Allow outgoing IPv6-in-IPv4 to interface ppp0
# iptables -A OUTPUT -o ppp0 -p ipv6 -j ACCEPT
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If you have only a static tunnel, you can specify the IPv4 addresses, too, like
Accept incoming IPv6-in-IPv4 on interface ppp0 from tunnel endpoint 1.2.3.4
# iptables -A INPUT -i ppp0 -p ipv6 -s 1.2.3.4 -j ACCEPT
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Allow outgoing IPv6-in-IPv4 to interface ppp0 to tunnel endpoint 1.2.3.4
# iptables -A OUTPUT -o ppp0 -p ipv6 -d 1.2.3.4 -j ACCEPT
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16.3.2.10. Protection against incoming TCP connection requests
VERY RECOMMENDED! For security issues you should really insert a rule which blocks incoming TCP connection requests. Adapt "-i" option, if other interface names are in use!
Block incoming TCP connection requests to this host
# ip6tables -I INPUT -i sit+ -p tcp --syn -j DROP
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Block incoming TCP connection requests to hosts behind this router
# ip6tables -I FORWARD -i sit+ -p tcp --syn -j DROP
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Perhaps the rules have to be placed below others, but that is work you have to think about it. Best way is to create a script and execute rules in a specified way.
16.3.2.11. Protection against incoming UDP connection requests
ALSO RECOMMENDED! Like mentioned on my firewall information it's possible to control the ports on outgoing UDP/TCP sessions. So if all of your local IPv6 systems are using local ports e.g. from 32768 to 60999 you are able to filter UDP connections also (until connection tracking works) like:
Block incoming UDP packets which cannot be responses of outgoing requests of this host
# ip6tables -I INPUT -i sit+ -p udp ! --dport 32768:60999 -j DROP
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Block incoming UDP packets which cannot be responses of forwarded requests of hosts behind this router
# ip6tables -I FORWARD -i sit+ -p udp ! --dport 32768:60999 -j DROP
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16.3.3. Demonstration example
Following lines show a more sophisticated setup as an example. Happy netfilter6 ruleset creation....
# ip6tables -n -v -L
Chain INPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 extIN all sit+ * ::/0 ::/0
4 384 intIN all eth0 * ::/0 ::/0
0 0 ACCEPT all * * ::1/128 ::1/128
0 0 ACCEPT all lo * ::/0 ::/0
0 0 LOG all * * ::/0 ::/0
¬ LOG flags 0 level 7 prefix `INPUT-default:'
0 0 DROP all * * ::/0 ::/0
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
¬
0 0 int2ext all eth0 sit+ ::/0 ::/0
0 0 ext2int all sit+ eth0 ::/0 ::/0
0 0 LOG all * * ::/0 ::/0
¬ LOG flags 0 level 7 prefix `FORWARD-default:'
0 0 DROP all * * ::/0 ::/0
Chain OUTPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
¬
0 0 extOUT all * sit+ ::/0 ::/0
4 384 intOUT all * eth0 ::/0 ::/0
0 0 ACCEPT all * * ::1/128 ::1/128
0 0 ACCEPT all * lo ::/0 ::/0
0 0 LOG all * * ::/0 ::/0
¬ LOG flags 0 level 7 prefix `OUTPUT-default:'
0 0 DROP all * * ::/0 ::/0
Chain ext2int (1 references)
pkts bytes target prot opt in out source destination
¬
0 0 ACCEPT icmpv6 * * ::/0 ::/0
0 0 ACCEPT tcp * * ::/0 ::/0
¬ tcp spts:1:65535 dpts:1024:65535 flags:!0x16/0x02
0 0 LOG all * * ::/0 ::/0
¬ LOG flags 0 level 7 prefix `ext2int-default:'
0 0 DROP tcp * * ::/0 ::/0
0 0 DROP udp * * ::/0 ::/0
0 0 DROP all * * ::/0 ::/0
Chain extIN (1 references)
pkts bytes target prot opt in out source destination
¬
0 0 ACCEPT tcp * * 3ffe:400:100::1/128 ::/0
¬ tcp spts:512:65535 dpt:22
0 0 ACCEPT tcp * * 3ffe:400:100::2/128 ::/0
¬ tcp spts:512:65535 dpt:22
0 0 ACCEPT icmpv6 * * ::/0 ::/0
0 0 ACCEPT tcp * * ::/0 ::/0
¬ tcp spts:1:65535 dpts:1024:65535 flags:!0x16/0x02
0 0 ACCEPT udp * * ::/0 ::/0
¬ udp spts:1:65535 dpts:1024:65535
0 0 LOG all * * ::/0 ::/0
¬ limit: avg 5/min burst 5 LOG flags 0 level 7 prefix `extIN-default:'
0 0 DROP all * * ::/0 ::/0
Chain extOUT (1 references)
pkts bytes target prot opt in out source destination
¬
0 0 ACCEPT tcp * * ::/0
¬ 3ffe:ffff:100::1/128tcp spt:22 dpts:512:65535 flags:!0x16/0x02
0 0 ACCEPT tcp * * ::/0
¬ 3ffe:ffff:100::2/128tcp spt:22 dpts:512:65535 flags:!0x16/0x02
0 0 ACCEPT icmpv6 * * ::/0 ::/0
0 0 ACCEPT tcp * * ::/0 ::/0
¬ tcp spts:1024:65535 dpts:1:65535
0 0 ACCEPT udp * * ::/0 ::/0
¬ udp spts:1024:65535 dpts:1:65535
0 0 LOG all * * ::/0 ::/0
¬ LOG flags 0 level 7 prefix `extOUT-default:'
0 0 DROP all * * ::/0 ::/0
Chain int2ext (1 references)
pkts bytes target prot opt in out source destination
¬
0 0 ACCEPT icmpv6 * * ::/0 ::/0
0 0 ACCEPT tcp * * ::/0 ::/0
¬ tcp spts:1024:65535 dpts:1:65535
0 0 LOG all * * ::/0 ::/0
¬ LOG flags 0 level 7 prefix `int2ext:'
0 0 DROP all * * ::/0 ::/0
0 0 LOG all * * ::/0 ::/0
¬ LOG flags 0 level 7 prefix `int2ext-default:'
0 0 DROP tcp * * ::/0 ::/0
0 0 DROP udp * * ::/0 ::/0
0 0 DROP all * * ::/0 ::/0
Chain intIN (1 references)
pkts bytes target prot opt in out source destination
¬
0 0 ACCEPT all * * ::/0
¬ fe80::/ffc0::
4 384 ACCEPT all * * ::/0 ff02::/16
Chain intOUT (1 references)
pkts bytes target prot opt in out source destination
¬
0 0 ACCEPT all * * ::/0
¬ fe80::/ffc0::
4 384 ACCEPT all * * ::/0 ff02::/16
0 0 LOG all * * ::/0 ::/0
¬ LOG flags 0 level 7 prefix `intOUT-default:'
0 0 DROP all * * ::/0 ::/0
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Generated: 2007-01-26 17:58:19