Special unicast addresses in IPv6 technology

In IPv6 technology, the address structure is worth further learning. The biggest difference between IPv6 and IPv4 is that IPv6 technology defines globally multicast addresses that can be clustered. This new concept may be vague, so we will explain this concept in this article.

What is an IPv6 clustered global unicast address?

The IPv6 protocol technology designs an Address with a hierarchical structure for point-to-point communication. This Address is called Aggregatable Global Unicast Address, which is defined in RFC2374. Clustering addresses have three levels of hierarchical structure:

Public topology: suppliers and exchange groups that provide public Internet transmission services;

Site topology: a specific local site or organization. Public transfer services are not provided to nodes other than the site;

Interface identifier: identifies the interface on the link;

The first three addresses are the prefix of the address type, which is used to distinguish other address types. The subsequent 13-bit tla id, 32-bit nla id, 16-bit sla id, and 64-bit host interface ID are used to identify the Top-down TLA Level Aggregator in the hierarchical structure, top aggregation), NLANext Level Aggregator, lower aggregation), SLASite Level Aggregator, site-Level aggregation) and host interface.

RES reserved for future TLA or NLA extension. TLA is a public network access point that is connected to long-distance service providers and telephone companies. It obtains the address from an international Internet Registrar such as IANA. NLA is usually a large ISP. It requests an address from TLA and assigns an address to the SLA. An SLA can also be called a subscriber). It can be an organization or a small ISP. The SLA is responsible for allocating addresses to its subscribers. The SLA usually assigns its subscribers an address block consisting of consecutive addresses so that these organizations can establish their own address hierarchical structure to identify different subnets. The bottom layer of the hierarchical structure is the network host.

The address format is designed to support both the clustering based on the current supplier and the new clustering type called the Exchange Board. Its Combination enables efficient route aggregation to be used to directly connect to the vendors and sites connected to the Exchange Board. The site can be connected to any of the two types of clustering points.

What is the difference between IPv6 Address Allocation and IPv4?

In IPv4, the address is owned by the user. That is to say, once a user applies for an address space from an organization, he will always use the address space, regardless of the Internet service provider's ISP. The disadvantage of this method is that the ISP must maintain a table item for each user's network number in the route table. As the number of users increases, there will be a large number of special routes that cannot converge. Even if there is no classless Inter-Domain Routing CIDR, such route table explosion cannot be handled.

IPv6 technology changes the address allocation mode from user-owned to ISP-owned. The global network number is assigned to the ISP by the Internet address allocation organization IANA. the user's global network address is a subset of the ISP address space. Whenever a user changes the ISP, the global network address must be updated to the address provided by the new ISP. In this way, the ISP can effectively control route information and avoid route explosion.