Reference:
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipv6/configuration/xe-3s/ipv6-xe-36s-book/ip6-multicast.
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When an interface is configured with IPv6 address, it automatically joins the all nodes (FF02::1) and solicited- node (FF02::1:FFxx:xxxx) multicast groups. The all-node group is used to communicate with all interfaces on the local link, and the solicited-nodes multicast group is required for link-layer address resolution. Routers also join a third multicast group, the all-routers group (FF02::2).

When Rapid PVST+ is used, switch ports always enter the blocking state immediately after the boot process
1. The blocking state is the first of the five possible port states in the Rapid PVST+ protocol. In this state, the port does not forward frames but listens to BPDUs to determine the location of the root bridge and the best path to reach it 12. After a port enters the blocking state, it transitions to the listening state and then to the learning state before finally entering the forwarding state. When Rapid PVST+ (Per-VLAN Spanning Tree Plus) is used, switch ports go through a specific state immediately after the boot process. This state is known as the "discarding" state.