I have a fiber connection to my ISP, that ends in a HUB like box. There are currently 2 routers and 4 computers connected. All with static IP addresses.

On one router I use the information I got from my ISP:

  • Client Host IPv6 Segment: 2001:xxxx:yyyy:FF00::/64
  • Client Host IPv6 Preset Gateway: 2001:xxxx:yyyy:FF00::FFFF/64

  • Client Router WAN Port IPv6 Address: 2001:xxxx:yyyy:FF00::0001/64

  • Client Router WAN Port IPv6 Gateway: 2001:xxxx:yyyy:FF00::FFFF/64

  • Client Router LAN Port IPv6 Address: 2001:xxxx:yyyy:0000::/56

  • DNS-1: 2001:b000:168::1

  • DNS-2: 2001:b000:168::2

My two ASUS routers RT-AC66U (office // multimedia) have the choices of connection type:

  1. Static IPv6
  2. Native
  3. Passthrough and others. I use STATIC IPv6 (no idea if others would be better)

What I want:

  1. I want a larger segment on my office router (IPv4 and IPv6)
  2. I want a larger segment on my multimedia router (IPv4 and IPv6)
  3. I want a small segment on each of the other computers (IPv4 and IPv6)
  4. I want to add many more IPv6 ONLY computers

In the IPv4 world I would change the Client Router WAN Port, the Client Host Segment (Netmask). How do I do that in IPv6???

migrated from serverfault.com Apr 15 '17 at 12:26

This question came from our site for system and network administrators.


I don't know what "host segment" is supposed to mean in your question. I do however notice that it is exactly the same as the WAN segment, so I am going to assume that it is the WAN segment.

Issues with your current configuration

Looking over your current configuration I notice two problems:

  • Your LAN prefix has the wrong length /56 rather than /64 which is the length you are supposed to be using on all link prefixes.
  • Both of the DNS servers are inside the same /64 which means there is likely a single point of failure which will take out both simultaneously once in a while.

Assuming the /56 is a routed prefix assigned by your ISP, that first problem can be fixed by assigning only a /64 to the LAN rather than an entire /56. A /56 is subdivided into 256 /64s, but in your case it appears the first of those is already assigned to the WAN, so you only have 255 left (which is probably more than you are going to need).

You can change 2001:xxxx:yyyy:0000::/56 into 2001:xxxx:yyyy:0001::1/64 for the LAN.

For DNS I suggest you use the DNS server provided by your ISP as the first sever and as the second server either host a recursor on one of your routers or use a public recursor.

Connecting two routers

How to connect two routers depends on what is supported by your ISP, which is something I cannot tell you, you'll have to ask them. It is possible that they only support one router directly connected, and traffic to the second router has to be routed through the first.

Ideally your ISP can split the /56 into two separate routed prefixes (for example two routed /60 prefixes and leaving the rest unallocated for the future) using the two routers as gateways. Maybe this can be achieved by having each router send DHCPv6 requests to the ISP. Maybe the ISP has a webinterface where this can be configured. Maybe the ISP does not support it at all.

Alternatively you can have the entire /56 routed to just one of the routers. That router can be configured to route a /60 to the other router. The connection between the two routers in this scenario can be done in a number of ways. What you want probably is to have this traffic between your routers go from the WAN port on the primary router to the WAN port on the secondary router. But it is also possible to use a LAN port on the primary router and connect that to the WAN port on the secondary router. Alternatively if your routers have enough segments you can use a third segment on each. Finally if the routers know VLANs you can use a VLAN tag as substitute for a third segment.

Just remember that connecting the LAN port of one router to a LAN port of the other router may have unintended consequences.

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