Analysis of IPv6 DNS servers

The premise for the commercial use of IPv6 is that IPv4 addresses are exhausted. For this reason, we urgently need the IPv6 protocol to improve this situation. So how does IPv6 distribute DNS servers? Next we will analyze the principles in depth. Hope to help you.

What is the architecture of the IPv6 Domain Name System?

The DNS in the IPv6 network is consistent with the IPv4 DNS in the architecture and uses a tree-like domain name space. The difference between the IPv4 protocol and the IPv6 protocol does not mean that the IPv4 DNS System and the IPv6 DNS system must be independent. On the contrary, the DNS system and domain name space must be consistent, that is, IPv4 and IPv6 share the same domain name space. During the transition from IPv4 to IPv6, the domain name can correspond to multiple IPv4 and IPv6 addresses at the same time. With the popularization of IPv6 networks, IPv6 protocol addresses will gradually replace IPv4 addresses. The only Root in the DNS tree structure), represented by the dot. The next Level of the root is called Top Level Domain, TLD), also known as Top Level Domain. The lower Level of the top-Level Domain is the Second Level Domain, SLD), the lower Level of the Second Level Domain is the third Level Domain, and so on. Each Domain is a subdomain of its parent Domain. For example, ".net.cn" is ". "cn", while "cnnic.net.cn" is both a subdomain of "net.cn" and ". the subdomain of cn.

Each node on the DNS tree has a Label. The root node ID is "null", that is, the length is 0), and the identification length of other nodes is between 1 and 63 bytes. The domain name of a node is composed of all the identifiers in the path from this node to the root node, which are arranged from left to right and separated. For example, http://www.cnnic.net.cn/

The entire Domain Name Space of DNS is divided into many zones), and data is stored in a distributed manner. Each zone has a Domain Name Server including the primary server and secondary server), and stores domain name information in the form of Resource Record. Resource records include host name domains), IP address ing, and authorization of subdomain servers.

When using the DNS service, you do not have to carefully understand the tree structure of the DNS domain name space. You only need to specify a DNS server or use dynamic hosts to configure DHCP when setting the network, this allows your applications to access the DNS system through the Resolver embedded in the operating system and query the network resource information related to the domain name.

How does IPv6 automatically discover DNS servers that provide resolution services?

(1) stateless DNS server discovery

The stateless DNS server automatically discovers the following methods:

Configure any multicast addresses within the site range for the DNS servers in the subnet. The node to be automatically configured sends a server Discovery request with the target address of this arbitrary play address, and queries DNS information such as the DNS server address, domain name, and search path. This request is sent to the nearest DNS server. Based on the request, the server answers DNS information such as the unicast address, domain name, and search path of the DNS server. The node configures the local DNS information based on the server's response. Later DNS requests will be sent directly to the DNS server using the unicast address.

In the same way as the first method, the multicast address or link multicast address within the site range is used instead of any multicast address within the site range.

IPv6 always uses any multicast address within the site as the address of the DNS server. All DNS resolution requests are sent to this multicast address. The nearest DNS server is responsible for parsing this request. After the resolution result is obtained, the result is returned to the request node, instead, the first method is to tell the node the DNS information such as the unicast address, domain name, and search path of the DNS server.

In terms of network scalability, security, and practicality, the first method is to use any broadcast address within the site as the DNS server address.

(2) stateful DNS server discovery

Stateful DNS server discovery uses DHCP-like servers to notify the node of DNS information such as the DNS server address, domain name, and search path. Of course, this requires additional servers.

In the transition phase from IPv4 to IPv6, how does one implement DNS?

During the transition from IPv4 to IPv6, the DNS service as the Internet infrastructure must also support the upgrade and conversion of this network protocol. You can use either of the following two methods to implement the DNS during the transition from IPv4 to IPv6:

(1) method of combining DNS-ALG and NAT-PT

IPv4 and IPv6 DNS are different in the record format, in order to realize the DNS query and response between IPv4 network and IPv6 network, the Application Layer Gateway DNS-ALG and NAT-PT can be combined, as a translator between IPv4 and IPv6 networks. For example, IPv4 address domain name ing uses the "A" record, while IPv6 uses the "AAAA" or "A6" record. Then, IPv4 nodes to IPv6 network DNS query request is "A" record, the DNS-ALG will "A" into "AAAA", and sent to the IPv6 network DNS server. When the server's answer arrives at the DNS-ALG, The DNS-ALG modifies the answer, change "AAAA" to "A", change the IPv6 address to the IPv4 translation address in the DNS-ALG address pool, inform the NAT-PT of the ing between the IPv4 translation address and the IPv6 Protocol address and return the IPv4 host as the resolution result. The IPv4 host uses this IPv4 translation address as the destination address to communicate with the actual IPv6 host through the NAT-PT.

(2) Dual-protocol stack

For A dual-protocol stack transition method, "A" record and "AAAA" or "A6" record exist simultaneously on the DNS server. Because the node can process both IPv4 and IPv6 protocols, there is no need to switch devices like dns alg. No matter whether the DNS server answers the "A" record or the "AAAA" record, it can communicate.