IP Addressing from Ethernet network

[dakhnod]

Hello,

my Thread interface has the following IP addresses:

        inet6 fe80::c8e4:3d1:99a6:7688  prefixlen 64  scopeid 0x20<link>
        inet6 fdd2:5640:49ae:1:cdb2:9b0c:9f00:4c0  prefixlen 64  scopeid 0x0<global>
        inet6 fdb7:5552:f959:a347:0:ff:fe00:4400  prefixlen 64  scopeid 0x0<global>
        inet6 fdb7:5552:f959:a347:3d52:a887:4c21:66ef  prefixlen 64  scopeid 0x0<global>
        inet6 fdb7:5552:f959:a347:0:ff:fe00:fc10  prefixlen 64  scopeid 0x0<global>
        inet6 fdb7:5552:f959:a347:0:ff:fe00:fc38  prefixlen 64  scopeid 0x0<global>
        inet6 fdb7:5552:f959:a347:0:ff:fe00:fc11  prefixlen 64  scopeid 0x0<global>

From experiments, I learned that a border router routes packets from ethernet -> thread network addresses to fdd2:5640:49ae:1:cdb2:9b0c:9f00:4c0.

When sending packets to fdb7:... through ethernet, the border router does not seem to forward them.

My questions are:

1. Why does the BR not route most of the addresses into the Thread network?
2. How is the fdd2:... prefix and IID calculated?
3. How can we make sure that the routable address (fdd2:...) doesn't change by itself, for example when the BR changes?

Thanks!

[jwhui]

The fdb7 prefix is the mesh-local prefix. It is not routable beyond the Thread mesh itself.

By design, the routable address (fdd2 in your example) may change to ensure different subnets are assigned different IPv6 prefixes. This is especially important in cases where the Thread mesh may partition / merge.

[dakhnod]

Thanks!

How can we address one device from ethernet, if its routable address could change?

[jwhui]

The typical answer is by using DNS-SD to resolve IPv6 addresses.

Check out the Thread Border Router - Bidirectional IPv6 Connectivity and DNS-Based Service Discovery codelab to learn more.