IPv6 address

If you are issued with an IPv6/64 range what should the IPv6 Prefix ID?

If you've only been delegated a /64 then you only have one subnet, so the prefix ID would be 0.

The only choice is 1 - 65535

The first 64 bits of the IPv6 address *are* the prefix, so if you've only been given a /64 assignment, the prefix is exactly what you were given by the ISP. This means you can only have one subnet (no routing between subnets for you).

A decent ISP will assign you either a /56 or a /48. That means there are 8 or 16 bits remaining for you to assign yourself to make LAN prefixes, meaning you can have either 256 LANs or 65536 LANs respectively.

[EDITED]

e.g. ISP gives you 2001:db8:abcd:ef00::/56

You can assign prefixes 2001:db8:abcd:ef00::/64 to 2001:db8:abcd:efff::/64 to up to 256 LANs.

"Prefix ID" is not a well-defined term, where do you see this - on a particular router perhaps? It might be asking for those 8 or 16 bits. If so, the first available value is zero.

Edited by candlerb (Fri 01-Dec-23 20:48:36)

Acutally I think the /56 its in the range of:
2001:0db8:ab00:0000:0000:0000:0000:0000 to 2001:0db8:ab00:00ff:ffff:ffff:ffff:ffff

And when you set it as a /64
2001:0db8:ab00:0000:0000:0000:0000:0000 to 2001:0db8:ab00:00ff:ffff:ffff:ffff:ffff

Green is the Prefix, Blue is the Subnet ID, Red is the Interface ID.

My ISP gives me a /48 Prefix and I put that into a Pool as a /64 Prefix which all our devices uses to create their IPv6 Address.

---
Paul

Edited by PaulKirby (Fri 01-Dec-23 19:19:18)

Yes you're right of course, I've editing the post. Thank you!

Thank you for establishing the value should be 0 which it won't accept. so I thought I would manually enter the prefix which is 2002:6456:2ec:: which it won't accept either, it says it is reserved for 6 to 4 tunnels. This is the address asigned by the isp, or should I be using a different address prefix?

It looks like your ISP doesn't do native IPV6.

The 2002::/16 prefix is used for 6to4, which requires the next 32 bits to be a global unicast IPv4 address.

That makes 2002:6456:2ec:: to be 100.86.46.* (I think). (or 100.86.2.36)?

Ipv6 still confuses me.

Edited by j0hn83 (Sat 02-Dec-23 15:01:29)

It would be 100.86.2.236, however using reserved IPv4 address, e.g. those provided by RFC 1918 or RFC 6598, to form 6to4 addresses is undefined and will not work.

In reply to a post by j0hn83:

That makes 2002:6456:2ec:: to be 100.86.46.* (I think). (or 100.86.2.36)?

hex 64 56 02 ec = 100.86.2.236

What does your router show as its IPv4 WAN address?

My guess is that you're behind CGNAT *and* your ISP doesn't have a clue about how to do IPv6.