Linux: Limit IPv6 connectivity to specific programs (opens in new tab)

At home my HE tunnel is snappier than the plain ipv4 from rr. The weird thing is it is not just a case of user perception (mine). One of the upstream s1 ntp boxes I sync with has ipv4 and ipv6 and is relatively close. I set one of my s1s to sync with both the ipv4 and ipv6 addresses of the machine and the ipv4 clock displayed a lower delay and less jitter while the offsets were seasonably close.

IPv6 is no longer necessarily preferred due to happy eyeballs. http://tools.ietf.org/html/rfc6555

You can always just drop ipv6 packets for certain destination ports (eg 80) with iptables if you know the application (like a browser) will be ok. Which is much simpler.

There is nothing special about firewalling off IPv6. NAT is not a security feature. The problem is that most consumer "routers" that people use nowadays are really: a router, a switch, a wireless access point, a firewall, and who knows what else. Here are some sample rules for firewalling off IPv4 (typed from memory, so use with caution):

  iptables -A INPUT -i lo -j ACCEPT
  iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
  iptables -A INPUT -s 192.168.1.0/24 -j ACCEPT
  iptables -A INPUT -p icmp -j ACCEPT
  iptables -A INPUT -j DROP
  
  iptables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
  iptables -A FORWARD -s 192.168.1.0/24 -j ACCEPT
  iptables -A FORWARD -p icmp -j ACCEPT
  iptables -A FORWARD -j DROP

Here are the IPv6 rules:

  ip6tables -A INPUT -i lo -j ACCEPT
  ip6tables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
  ip6tables -A INPUT -s 2001:xx:xx:xx::/64 -j ACCEPT
  ip6tables -A INPUT -p ipv6-icmp -j ACCEPT
  ip6tables -A INPUT -j DROP
  
  ip6tables -A FORWARD -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
  ip6tables -A FORWARD -s 2001:xx:xx:xx::/64 -j ACCEPT
  ip6tables -A FORWARD -p ipv6-icmp -j ACCEPT
  ip6tables -A FORWARD -j DROP

Does that look like it would be hard to do? Your router should come with these rules already. If it does not, ditch it and buy one that is supported by OpenWRT, where IPv6 support is not a second class citizen.

Edit: Naturally, IPv4 rules would have to be more complicated since you'll want to have your NAT setup in there. In this way, configuring IPv6 is actually easier :). Also, a real router would have rules set up for throttling certain types of traffic (e.g.: you don't want more than, say, 1000 ICMP messages per second). However, all those steps are identical for IPv6.

What's the point of assigning an address to every node on the Internet if you can't connect to these addresses.

The advantage of IPv6 is that any computer can act as a server again. NAT makes it unnecessarily difficult to build simple peer to peer applications such as for telephony, remote access or file transfer.

I agree - that line from the article makes no sense. Not having NAT is awesome because NAT is a nasty hack that doesn't add any security.

The tunnelling scenario is valid though - because they add quite a bit of latency so you might not want to use it for everything.

If you with the commercial router route, checkout OpenWRT / DD-WRT / Tomato. There are several forks, so depending on what features you want, and what hardware you have, you may opt for a different version. If you go with an existing x86/amd64, just install your favorite distro and start reading up on iptables configuration and management. While iptables to be quite powerful in terms of features, I find its' syntax is painful. There are several projets aiming to simplify this, by generating rules from another, simpler, DSL but it adds complexity. This is why I prefer PF, but that requires you to install OpenBSD instead of Linux. If you know your way around UNIX, and are ready to read up the FAQ and man pages, this shouldn't be a problem :).

Openwrt https://openwrt.org/ is where most of the docs are, though there are other similar projects. The most supportive vendor is probablr Netgear now http://www.myopenrouter.com/

Not exactly a common use case or linux related but my Red Alert 2 game patched for tcp/ip instead of IPX support it shipped with will only let you into LAN game lobbies on ipv6, you can't see any games to join. ipv4 and it works like a charm.

My point is just that I'm sure some very very weird stuff can happen with software.