Tag Archives: IPv6 Global Unicast Address

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IPv6 VPN Routing with Dynamic Prefixes

How to route traffic inside an IPv6 site-to-site VPN tunnel if one side offers only dynamic IPv6 prefixes? With IPv4, the private network segments were statically routed through the tunnel. But with a dynamic prefix, a static route is not possible. That is, a dynamic routing protocol must be used. Here is an example of how I used OSPFv3 for IPv6 between my VPN endpoints.

In detail, I have a home office with a dual stack ISP connection. However, this connection has a dynamic IPv6 prefix: After every reboot or lost connection of the firewall, I get a new IPv6 prefix. This is really bad for building a site-to-site VPN to the headquarter. Since I don’t want to use any kind of NAT/NPTv6 with unique local addresses, I am talking OSPFv3 over the VPN tunnel in order to route the dynamic prefix range (global unicast) via the tunnel.

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IPv6 Site-to-Site Reommendations featured image

IPv6 Site-to-Site VPN Recommendations

With global IPv6 routing, every single host has its own global unicast IPv6 address (GUA). No NAT anymore. No dirty tricks between hosts and routers. Great. Security is made merely by firewalls and policies. Site-to-site VPNs between partners can be build without address conflicts. Great again!

However, one problem to consider is the proper IPv6 routing via site-to-site VPNs since both sides now can reach each other even without a VPN. This was (mostly) not true with IPv4 in which both partners heavily relied on private RFC 1918 addresses that were not routable in the Internet. If specific IPv6 traffic should flow through a VPN but does actually traverse the Internet, it would be easy for a hacker to eavesdrop this traffic, leading to a security issue!

The following principles should be realized properly to assure that IPv6 traffic is never routed through the mere Internet when a site-to-site VPN tunnel is in place. Even in a failure of that tunnel. The principles can be applied to any IPv6 tunnels between partners, remote sites, home offices, etc., as long as the other site has its own global unicast IPv6 address space. (For VPNs in which a sub-prefix from the headquarters prefix is routed to a remote site, the situation behaves different. This article focuses on the routing between different IPv6 adress spaces.)

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