[j-nsp] IPv6 duplicate: Can't assign requested address

[Markus]

A friend has a MX480 with 11.4R2.14

He tried to bring up 4 new BGP transit peers (different providers) via 
IPv6. And got "Can't assign requested address" when bringing the local 
IPv6 up, for each address. And show interfaces shows "Duplicate" IPv6 
addresses.

First idea would be that another device has assigned itself the IPv6 
address, but there are no other devices in the link except a switch, and 
each logical link is on its own VLAN. Also, it happens for all 4 
providers addresses, not just one. How to troubleshoot such a situation?

A workaround was to add

dad-disable;

under the interfaces configuration for that unit.

The providers each gave him a /126 as the transfer network. Each 
transfer network is in its own VLAN. E.g.:

unit 900 {
description "Transit 1";
vlan-id 900;
family inet {
address 95.248.119.126/30;
}
family inet6 {
address 2b01:12d8:0:2::2/126;
}

show interfaces xe-0/1/0.900

Logical interface xe-0/1/0.900 (Index 196622) (SNMP ifIndex 542)
[...]
Protocol inet6, MTU: 1500
Addresses, Flags: Is-Preferred Is-Primary Duplicate
Destination: 2b01:12d8:0:2::/126, Local: 2b01:12d8:0:2::2
INET6 Address Flags: Duplicate
Addresses, Flags: Is-Preferred Duplicate
Destination: fe80::/64, Local: fe80::8618:8801:5c06:1052
INET6 Address Flags: Duplicate

Thanks!
Markus