Supplementary content about IPv6 address Definition

In the previous article, we talked about a lot of IPv6 address-related content and learned the differences between IPv6 addresses and traditional version IP addresses and the meanings of some new content, now let's expand this part of content. Now we will talk about multicast addresses, fields, and some definitions.

IPv6 multicast addresses recognize multiple interfaces. Use an appropriate multicast routing topology to send packets sent to the multicast address to all interfaces identified by the address.

IPv6 multicast addresses have a format prefix FP of 1111 1111 ). IPv6 addresses are easy to distinguish between multicast addresses because they always start with FF. Multicast addresses cannot be used as source addresses.

In addition to FP, multicast addresses include other structures to identify their logos, scopes, and multicast groups, as shown in.

The fields in the multicast address are as follows:

Flag: the "flag" field indicates the flag set on the IPv6 multicast address. The size of this field is 4 bits. The unique identifier defined from RFC 2373 is the Transient T) identifier. The T sign uses the low bit of the flag field. When it is set to 0, the t sign indicates that the multicast address is a well-known) multicast address permanently assigned by the Internet Number Assignment organization IANA. When it is set to 1, the t sign indicates that the multicast address is a transient non-permanent assignment) multicast address.

Scope: the scope field indicates the scope of the IPv6 network for multicast communication. The size of this field is 4 bits. In addition to the information provided by the multicast routing protocol, the router uses the multicast scope to determine whether multicast communication can be forwarded.

The following scopes are defined in RFC 2373:

Scope field value range: 1 node local, 2 link local, 5 site local, 8 Local, E global

For example, communication using the multicast address FF02: 2 has a local link scope. The IPv6 router will never forward the communication to a local link.

Group ID: the "Group ID" field identifies multicast groups and is unique in the scope. The size of this field is 112 characters. The permanently assigned group ID is independent of the scope. The transient group ID is only related to a specific scope. The multicast address from FF01: To FF0F: is a reserved known address.

To identify all nodes used for local node and Local Link scope, define the multicast addresses of the following IPv6 addresses:

FF01: 1. All node addresses in the local scope of a node)

FF02: 1. All node addresses in the local scope of The Link)

To identify all routers used for local nodes, local links, and local scope of the site, define the following multicast addresses:

FF01: All vro addresses in the local scope of Node 2)

FF02: 2. All router addresses in the local scope of The Link)

FF05: 2. All vro addresses in the local scope of the site)

If 112 bits are used in the group ID, there may be a 112-Power Group ID of 2. However, because IPv6 multicast addresses are mapped to Ethernet multicast MAC addresses, RFC 2373 recommends that you assign a "group ID" from a low 32-bit IPv6 multicast address ", set the remaining original group ID to 0. Each group ID is mapped to a unique Ethernet multicast MAC address.

Request Node Address: The request Node Address facilitates effective network node query during address resolution. In IPv4, ARP request frames are sent to MAC-level broadcasts, disrupting all nodes in the network segment, including nodes that do not run IPv4. IPv6 uses the "neighbor request" message to perform address resolution. However, all node addresses in the local link scope are not used as the target of the "neighbor request" message, because this may disturb all IPv6 nodes on the local link, but use the multicast address of the Request node. The multicast address of the Request node consists of the prefix FF02: 1: FF00: 0/104 and the last 24 addresses of the resolved IPv6 address.

For example, for a node that uses the local IPv6 address of the FE80: 2AA: FF: FE28: 9C5A link, the corresponding request Node Address is FF02: 1: FF28: 9C5A. To resolve the FE80: 2AA: FF: FE28: 9C5A address to its link layer address, the node sends a "neighbor request" message to FF02: 1: FF28: 9C5A request Node Address. When FE80: 2AA: FF: FE28: 9C5A is used, multicast communication of the Request Node Address is listened because it corresponds to the interface of a physical network adapter, you have registered a multicast address with the network adapter.

The result of using the multicast address of the Request node is that address resolution usually occurs on the link. You do not need to use a mechanism to disrupt all network nodes. In fact, few nodes are disturbed during address resolution. In practice, because of the relationship between the Ethernet MAC address, IPv6 Interface ID, and the request Node Address, the request Node Address plays the role of a pseudo Unicast address to achieve very effective address resolution.