IPv6: LL address is occasionally the wrong one

RouterOS General
1 
[nsayer@KFU] > int br print
Flags: X - disabled, R - running 
 0  R name="bridge1" mtu=1500 l2mtu=1520 arp=proxy-arp mac-address=00:0C:42:A9:0F:62 protocol-mode=none priority=0x8000 auto-mac=yes admin-mac=00:00:00:00:00:00 max-message-age=20s forward-delay=15s transmit-hold-count=6 ageing-time=5m 
[nsayer@KFU] > ipv6 ad print
Flags: X - disabled, I - invalid, D - dynamic, G - global, L - link-local 
 #    ADDRESS                                     FROM-POOL INTERFACE                                                                                                                                                                                                 ADVERTISE
 0  G 2601:9:4980:52::/64                                   bridge1                                                                                                                                                                                                   yes      
 1 DL fe80::20c:42ff:fea9:f5d/64                            ether1-gateway                                                                                                                                                                                            no       
 2 DL fe80::20c:42ff:fea9:f5e/64                            bridge1

Now, I’d expect the LL address to end in f62, not f5e.

This causes IPv6 routing to break on occasion, since sometimes ff02::2 on that segment yields f62 and sometimes f5e. I’m not entirely sure why it seems to flap back and forth.

2

After a couple of back-n-forths with Support, the upshot is that this is expected behavior. If you want your bridge to have a mac address that doesn’t change (and thus, a LL address that doesn’t change), then you must hard-code an admin-mac.

I’ve done that, and after a reboot the LL address of the bridge now is the EUI-64 of the admin mac, and that should result in a stable IPv6 route.