Thanks for the tip on IGMP snooping! It was absolutely breaking connectivity for me on daisy-chained switches trying to ping Google's IPv6 DNS.I know this is an old thread but maybe someone will be searching for the solution to the same issue like I was last night...
Basically in my case the end effects were pretty much exactly like OP described:
Hosts in the same subnet (local LAN) get local and global ipv6 fine. They can ping each other OK using local and global ipv6 but pinging or otherwise accessing external global ipv6 fail initially.
Notice the bolded "initially" because it's important! Basically I discovered that once the router had recorded successfully the host in terms of ipv6 neighbor discovery the pings to outside (eg. ipv6.google.com) start working!
I was able to reproduce this every time by changing the default privacy setting on the interface of my test host from "default" to "prefer temporary addresses". This is important because unlike ipv4's ARP - it's not possible to clear the ND (neighbor discovery) cache on mikrotik. This causes the host to generate a new IPv6 every time the interface gets up which in turn will guarantee that the router will not have it in it's ND cache and pings initially fail. So once you have a fresh uncached (ND) ipv6 address on the host you ping eg. ipv6.google.com and see that pings fail.
In the meantime you ping the router's global IPv6 address which will cause it to "notice" (discover) the new IP and record it and then magically pings starts to reply.
It turned out that the problem was caused by "IGMP snooping" set to ON on the LAN bridge. Once I've changed that back to OFF everything started working OK. I found the hint to this in viewtopic.php?t=155797 so hopefully it will help anyone experiencing similar issues.
Statistics: Posted by Aerowinder — Fri Jan 19, 2024 5:16 pm