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Does anyone how to redirect an incoming port to another port for an IPv6 address in OpenWRT?

There is no NAT involved just an ordinary global IPv6 address.

What I am trying to do is change the port of SSH for a number of servers; redirecting an arbitrary port number to 22 internally. Whilst remaining on port 22 for the local network.

E.g. [2345::1]:5000 -> OpenWRT -> [2345::1]:22

When using the equivalent IPv4 NAT this configuration is very simple because the ports can easily be configured with port forwarding.

Many thanks

  • I'm not sure why you wouldn't just configure those servers to additionally listen on port 5000... – grawity Aug 19 '18 at 22:42
  • ^, and then simply block port 22 for WAN inbound connections. – confetti Aug 19 '18 at 23:19
  • yes that would be an alternative, but doing it once on the router is preferable to configuring many servers – jacob_pro Aug 19 '18 at 23:25
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You can actually use the same DNAT-based port forwarding in Linux ip6tables as well. The main difference is that you don't change the destination address; on the other hand, you do need to match on the existing address.

-t nat -I PREROUTING -d 2345::1 -p tcp --dport 5000 -j DNAT --to-destination [2345::1]:22

Of course, with IPv6 you don't need SNAT-based masquerading, but that's a completely separate firewall rule to begin with, so it can be simply omitted.

I don't know how this translates to OpenWRT (except that you might need the kmod-ipt-nat6 package), but I suspect it's something like:

config redirect
    option family ipv6
    option src wan6
    option src_dip 2345::1
    option proto tcp
    option src_dport 5000
    option target DNAT
    option dest_ip 2345::1
    option dest_port 22
  • thanks very much. I have installed kmod-ipt-nat6 and have been using the following command (i haven't got it working with the openwrt UCI config yet): ip6tables -t nat -I PREROUTING -d IPV6_ADDRESS -p tcp --dport 5000 -j DNAT --to-destination [IPV6_ADDRESS ]:22 however it will only work if i also open port 22 from WAN to the device in the firewall - which leaves me stuck with the original problem of 22 being open. the redirect from 5000 is working - but how can I limit access to only 5000 and not 22 as well? – jacob_pro Aug 20 '18 at 23:12
  • as far as i can see "config redirect" is not supported for ipv6? github.com/openwrt/luci/issues/925 – jacob_pro Aug 21 '18 at 15:33
  • You can allow DNAT-ed connections to port 22 (first) and then DROP any NEW connections to port 22 in your FORWARD chain. – Tomek Aug 21 '18 at 21:04
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It does not appear to currently be possible to use "config redirect" for IPv6 in OpenWRT's firewall 3.

However I was able to manually achieve it using the following rules:

ip6tables -t nat -I PREROUTING -d IPV6_ADDRESS_HERE -p tcp --dport 5000 -j DNAT --to-destination [IPV6_ADDRESS_HERE]:22 ip6tables -A zone_wan_input -m conntrack --ctstate DNAT -j ACCEPT ip6tables -A zone_wan_forward -m conntrack --ctstate DNAT -j zone_(ZONE_NAME)_dest_ACCEPT

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