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Because devices in your LAN will all be accessible from the internet with IPv6, you need to firewall every device.
It becomes more of a problem for IoT devices which you can't really control. If you can, disable ipv6 for those.
Haha, no not really. IPv6 has the ability to provide public IP address for each device, but that doesn't mean it will have to. Other than number of possible addresses, nothing is different. Routing, firewalls, NATs, etc. All remains the same.
IPv6 doesn't support NAT... Or am I woefully out of date.
But your home router will just firewall like it does already but you don't have NAT as a simple fall back for "security". It does make running internal services much easier as you no long need to port forward. So you can run two webservers on port 80 and they be bother allowed inbound without doing horrible load balance or NAT translation.
IPv6 has NPTv6, which allows you to translate from one prefix into another.
Useful if you've got dual WAN, and can't advertise your own addressing via the ISP. You can use NPTv6 to translate between your local prefix and the public prefixes. But NPTv6 is completely stateless. It's literally a 1:1 mapping between the prefixes.
IPv6 has both NAT66 and NPTv6. (Note that NPTv6 was once called NAT66 too, but I am referring to the "stateful, one-to-many" NAT66 here. Yeah, it's confusing.) NAT66 is more like the traditional stateful NAT that all of us know and understand.
Ipv6 doesn't need NAT
The router does have a firewall but it blocks everything inbound by default. Some routers (at least mine) do not offer the granularity to filter traffic for certain devices (no NAT either). It's either allow all in or nothing.
When you enable IPv6 and switch off the firewall (since you can't host anything otherwise), every device becomes exposed to the internet.
Then unless the devices have a firewall themselves, all is exposed. Not just the web services, ssh and the rest as well.
There was a way around it however but not something everyone will be able to do with their home router. I had to ssh to the router using ISP admin credentials leaked on the internet, then create a file in init.d that loads a custom iptables file with the firewall rules I needed for IPv6. NAT for IPv6 however was not supported by the kennel used for my router.
Wait, ipv6 doesn't require port forwarding to expose something to the internet?
Port forwarding is exclusively a NAT phenomenon.
In IPv6 every device should in theory have a public address - just like how every computer had a public IPv4 address back in the 1980s ~ 1990s.
However, most sensible routers will have a firewall setup by default that blocks all incoming connections for security reasons. You still need to add firewall rules.
This is correct. My router however doesn't have that level of firewall. It's either all allowed or nothing is.
There's no "should in theory". It's only a possibility due to sheer number of possible combinations. No one was ever going to make every device public. It makes absolutely no sense. Why would your company's printer be online or isolated networks or VPNs? There's no point.
IP addressing is just a way to give a globally unique number to each device. It's just a number.
And there wasn't a real public/private distinction when the Internet was still in its infancy. Printers were indeed given "public" addresses because people needed a number for it.
If you don't want your printer to be reachable by the public Internet, use a firewall to block outside connections. If you can use NAT, you certainly can use a firewall. Heck, they are almost the same thing if you have been using the Linux kernel (iptables/nftables handle firewalling and masquerading with the same tool!)
Routability is not the same as reachability. With NAT transversal you can reach my "private" hosts all the same, although you can't route to me because I don't have a public address.
It's not necessary to firewall every device. Just like how your router can handle NAT, it should be able to handle stateful firewall too.
Mine blocks all incoming connections by default. I can add (IP, port range) entries to the whitelist if I need to host a service, it's not really different to NAT port forwarding rules.
So even though the device has a public address, the route is through the firewall, hence the ability to filter traffic?
Yes, the firewall is still your transition point from your internal network to your ISP network. Just like with ipv4, you should be configuring your ipv6 firewall to only allow designated traffic into your network from the internet.
Right. Packets still have to go through your router, assuming that your router has firewall turned on, it goes like this:
Your router receives a packet.
It checks whether the packet is "expected" (a "related" packet) - by using connection tracking.
For example, if ComputerA had sent something to ServerX before, and now the packet received by router says "from ServerX to ComputerA", then the packet is let through - surely, this packet is just a reply to ComputerA's previous requests.
If step 2 fails - we know this is a new incoming packet. Possibly it comes from an attacker, which we don't want. And so the router checks whether there is a rule that allows such a packet to go through (the assumption is that since you are explicitly allowing it, you know how to secure yourself.)
If I have setup a firewall rule that says "allow packets if their destination is ComputerB, TCP port 25565", and the received packet matches this description, the router lets it through.
Finally, the packets that the router accepts from the previous steps are forwarded to the relevant LAN hosts.
I understand this part :) I use a fairly complex firewall at work though I only know bits and pieces from reading different manuals. I think the part I didn't understand was how exactly the routing worked differently in IPv4 vs v6. I get that because NAT happens in IPv4, packets can't be routed at all without the firewall/router but I wasn't sure what was the mechanism by which v6 made sure that packets went through the router, especially when you have stuff like v6 DHCP relays.
Ah, I misunderstood your original comment, oops! But yes, IPv6 packets are routed just like IPv4 ones, just without the NAT'ing process i.e. the packet remains untouched the entire trip.
The argument for IPv6 that there could be a unique address for 200 devices for every person living on the planet was much more compelling when network security was a more simple space.
Nothing has changed about why that is compelling: NAT sucks and creates nothing but problems.
Network security is almost the same with IPv6.
If you rely on NAT as a security measure you are just very bad at networking.
I mean that, when IPv6 started filtering out to non-specialists, network security wasn't nearly as complex, and nor was the frequency of escalation what it is today. Back when IPv6 was new(ish), there weren't widespread botnets exploiting newly discovered vulnerabilities every week. The idea of maintaining a personal network of internet-accessible devices was reasonable. Now maintaining the security of a dozen different devices with different OSes is a full time job.
Firewalling off subnets and limitting the access to apps through a secured gateway of reverse proxies is bot bad networking. That's all a NAT is, and reducing your attack surface is good strategy.