Hi bgp players, just saw this, and I can tell you good news.
It works, solid establised bgp session on Vultr + RouterOS (Both v6 and v7).
Answer your question:
1.
Q: What should I set the next hop to for the BGP peer route as default gateway is leant via RA? Should it be the link local address or the interface ipv6 address?
A:
Case1: before you use dd command to write raw image, take a note your ipv6 gateway address.
Case2: you already in RouterOS:
Get your gateway mac-address, from Winbox -> IP -> ARP.
Convert that to IPv6 local-address. For example, use this online tools.
https://ben.akrin.com/mac-address-to-ip ... converter/
ADD a ipv6 route, NO NEED to add default router (I mean no ::/0). dst.address is your bgp peer address (get it from vultr panel
https://my.vultr.com/subs/?id=your-inst ... id#subsbgp, Vultr's ipv6 addres, not your instance address. ), gateway is that link-local address your found with your interface name, for example: "fe80::fc00:aaa:aaaa:aaaa
%ether1"
2.
Q: What should I set the scope and target scope for the BGP routes using routing filters?
A: If i remember it correctly, you don't need to adjust that to make it works. as bgp with vultr works with
Routeros v6, at that time mikrotik does not support recursive routes on IPv6, maybe I just rewrite to link-local or use default.
I current have it default as :
To vultr peer address: (scope:30, target scope:10, gateway: gw-link-local-address-you-found-in-q1)
Router received from BGP: Scope 40, target scope: 30 gateway: vultr-bgp-address)
From now, you shoud success ping your peer address.
Add bgp peers, enable multihop, like normal.
I forget if I configure that, or if it's a best practice, but it works on version 7.7rc5(and before, except some buggy version I don't remember)
If you have more question on this, you can contact bgp players (like, from dn42 unofficial telegram group/ others), thay have master experience on BGP @ RouterOS @ Vultr.