Hi, all.

My experiment is to test lwip 2.1.2 IPv6 address auto-configuration with two different routers.
And check whether IPv6 address auto-configuration is successful.
Unfortunately, the test failed.

My test board is running lwip2.1.2 and there are 3 IPv6 address for the Ethernet netif.
Slot 0 is link local, slot 1 is for global address, slot 2 is for auto-configured address.
My test board can setup auto-configuration IPv6 address with the Router 1 with valid time of 604800 seconds(7 days).
The following address is the auto-configured address 1 with valid time of 604054.
FC00::D51:200:DFF:FE41:1, 604054
When I unplug the Ethernet cable, the auto-configured address 1 with prefix of Router 1 is still there and the valid time is counting down.
FC00::D51:200:DFF:FE41:1, 604038
When I plug the Ethernet cable to the Router 2, no new auto-configured IPv6 address will be generated for prefix of Router 2(FC00:0:0:5B1::/64).
I think when the valid time of auto-configured address 1 is expired, another new address with prefix of Router 2 may generated.
But, this is 7 days later which is not reasonable.

I used the same procedure to test my laptop which is windows 10 with IPv6 auto-configuration enabled on Ethernet interface.
I connected my laptop to the two Routers one by one, everything works fine.
I notice that when I connect my laptop to Router 2, the valid time of the auto-configuration IPv6 address with prefix of Router 1 is reduced to 3 seconds from a 6 days.
And after 3 seconds, the former auto-configured address is disappear and new auto-configured address is generated with prefix of Router 2.
The procedure is as follows:
Interface 16: Ethernet 5
Address type   DAD     Valid time   Preferred time   Address
---------  ----------- ---------- ---------- ------------------------
Public         No         6d23h59m50s  23h59m50s fc00::d51:8c79:e4f9:f5a3:e5eb
Tentative         No         6d23h59m44s  23h57m15s fc00::d51:9146:165c:cb7f:f35a
Other        No            infinite   infinite fe80::8c79:e4f9:f5a3:e5eb%16

Interface  16: Ethernet  5
Address type   DAD     Valid time   Preferred time   Address
---------  ----------- ---------- ---------- ------------------------
Public         Preferred                 3s         3s fc00::d51:8c79:e4f9:f5a3:e5eb
Tentative    Preferred                 3s         3s fc00::d51:9146:165c:cb7f:f35a
Other          Preferred           infinite   infinite fe80::8c79:e4f9:f5a3:e5eb%16

Interface 16: Ethernet  5
Address type   DAD     Valid time   Preferred time   Address
---------  ----------- ---------- ---------- ------------------------
Public        Preferred        6d23h59m59s  23h59m59s fc00::5b1:8c79:e4f9:f5a3:e5eb
Tentative   Preferred        6d23h59m59s  23h57m30s fc00::5b1:b0de:2e31:256f:afcd
Other        Preferred           infinite   infinite fe80::8c79:e4f9:f5a3:e5eb%16

From the test, we can see that when a new router is connected, windows 10 will set the valid time of the former prefix to 3 seconds to make it expired quickly,
then new address will be generated.

So, how to make lwip behave like windows 10 under such circumstances?