2.8. A Node's Required Addresses

Host Required Addresses

A host is required to recognize the following addresses as identifying itself:

1. Link-Local Address for each interface (Link-Local Address)

2. Any additional unicast and anycast addresses that have been configured for the node's interfaces (manually or via automatic address configuration)

3. The Loopback Address (Loopback Address, ::1)

4. All-Nodes Multicast Addresses defined in Section 2.7.1 (All-Nodes Multicast Addresses)

   • FF01::1 (interface-local all-nodes)
   • FF02::1 (link-local all-nodes)

5. Solicited-Node Multicast Address for each of its unicast and anycast addresses (Solicited-Node Multicast Address)

6. Multicast addresses of all other groups to which the node belongs

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Router Required Addresses

A router is required to recognize all addresses that a host is required to recognize, plus the following addresses as identifying itself:

1. Subnet-Router Anycast Addresses for all interfaces that are configured to act as a router (Subnet-Router Anycast Addresses)

2. All other Anycast Addresses with which the router has been configured

3. All-Routers Multicast Addresses defined in Section 2.7.1 (All-Routers Multicast Addresses)

   • FF01::2 (interface-local all-routers)
   • FF02::2 (link-local all-routers)
   • FF05::2 (site-local all-routers)

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Address Requirements Summary

Minimum Host Address Requirements

Required addresses:
├── Unicast addresses
│   ├── Link-local address (per interface)
│   ├── Loopback address (::1)
│   └── Other configured unicast/anycast addresses
│
└── Multicast addresses
    ├── FF01::1 (interface-local all-nodes)
    ├── FF02::1 (link-local all-nodes)
    ├── Solicited-node addresses (per unicast/anycast address)
    └── Other joined multicast groups

Minimum Router Address Requirements

Required addresses:
├── All host required addresses
│
├── Anycast addresses
│   └── Subnet-router anycast addresses (per router interface)
│
└── Multicast addresses
    ├── FF01::2 (interface-local all-routers)
    ├── FF02::2 (link-local all-routers)
    └── FF05::2 (site-local all-routers)

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Important Notes

1. Link-local addresses are mandatory: Every IPv6 interface must have at least one link-local address, even if that interface does not have a global unicast address.

2. Solicited-node multicast addresses: For each configured unicast or anycast address, a node must join the corresponding solicited-node multicast address. This is critical for the normal operation of the Neighbor Discovery Protocol.

3. Additional router requirements: Routers must support all host address requirements in addition to router-specific anycast and multicast addresses.

4. Dynamic address management: When addresses are added or removed (whether manually or through automatic configuration), corresponding solicited-node multicast addresses must also be joined or left accordingly.