Network Layer 2 (IPv4 and IPv6 addresses and related protocols)

Network Layer 2 (IPv4 and IPv6 addresses and related protocols) IP (internet protocol) protocol is the core protocol of the TCP/IP protocol family and the network layer of the internet. The current version number is 4, also known as IPv4. The next generation IP protocol version number is 6, that is, IPv6. As described in the network layer function, the IP layer provides the selection and forwarding functions for the Internet. Hosts connected to the Internet can communicate with each other through the IP layer. On the IP layer, IP addresses are used to identify the interfaces connected to the network and then identify a host. When the information is transmitted in the TCP/IP protocol stack, each layer adds its own control information, that is, the protocol header, and the IP address is added to the IP header. The IP header provides IP protocol and datagram information. 1. IPv4 datagram format when two devices connected to the network communicate with each other through the IP layer, the interactive information is encapsulated into a network layer group, and the network layer group is also called a datagram. The IPv4 datagram format is as follows: the meaning of each field is as follows: Version Number: Protocol version number, IPv4 is 4, IPv6 is 6 (of course, the IPv6 Header is not exactly like this, but four bits have the same meaning) Header Length: the header length refers to the number of 32 bits in the header, including any options. Therefore, the IPv4 header can be up to 60 bytes of service type: the service type (TOS) field contains a 3-bit priority subfield (which has been ignored now ), the 4-bit TOS subfield and the 1-bit unused bit must be set to 0. 4-bit to s represents the minimum latency, maximum throughput, maximum reliability, and minimum cost datagram length: the length of the entire IP datagram in bytes (including the header ). Identifier, flag, and offset: identifies each IP datagram sent by the host. The logo and slice offset are used to support IP Fragment. Of course they must be used together with the logo. IPv6 cannot be sharded on the vro. in IPv6, the shard and reorganization must survive at the source and destination: the number of vrouters that the datagram can pass through, this will cause the IP datagram to disappear in the network sooner or later, that is, it will either disappear or "die" due to the time of survival: Identify the protocol type of the previous layer carried by the IP layer, for example, UDP/TCP/SCTP. First checksum: The first checksum and field are the checksum and code calculated based on the I P header. The IPv6 Header does not contain the header checksum. Source and Destination addresses: source IP addresses and destination IP address options: the last field is any option, which is an optional variable length information in the datagram. It mainly includes: security and processing restriction record path (let every vro write down its I p address) timestamp (let every vro write down its I P address and time) loose Origin Site routing (specifying a series of mandatory I P addresses for the datagram) Strict Origin Site routing (similar to loose Origin Site routing, but only the specified addresses are required, cannot go through other addresses ). 1. The IP fragment data link layer generally limits the maximum length of data frames sent each time. When the IP layer receives an IP data report to be sent, it must determine which local interface to send data (optional) and query the interface to obtain its MTU. The IP address compares MTU with the datagram length, and fragment if necessary. Fragments can occur on the original sending host or intermediate router. However, only the final destination of the multipart packet will be reorganized. Re-assembly is completed by the IP layer of the destination. The purpose is to make the partitioning and re-assembly process transparent to the transport layer (such as TCP. The IP header contains an ID field set by the original datagram sender, which is unique in the IP datagram sent by the sender. This value is copied to each piece when the data packet is sharded. The flag field uses a bit to represent "more slices ". Except for the last piece, the bit must be set to 1 for each piece of data. The offset field refers to the position at the beginning of the offset of the original datagram. In addition, after the data packet is split, the total length value of each piece should be changed to the length value of the piece. One bit in the flag field is called the "not sharding" bit. If this bit is set to 1, the IP address does not shard the datagram. In this case, if the vro determines that a shard is required, it discards the datagram and sends an ICMP error message ("Shard is required but no shard bit is set") to the source host of the datagram.
When an IP datagram is sharded, each segment becomes a group with its own IP header and is independent from other groups when routing is selected. In this way, the data packets may be out of order when they arrive at the target end, but there is enough information in the IP header to allow the receiving end to correctly assemble the data packets.
However, IP fragmentation has a serious defect: The whole datagram should be re-transmitted even if only one piece of data is lost. In IPv6, the shard function is restricted to the source host because the shard increases the workload of the network core (that is, the router), and it has to judge the processing of all packets, the network core should focus more on its selection and forwarding functions, rather than being interrupted by additional processing. 2. IPv4 addresses are connected to the network through interfaces on both the host and vro over the Internet. An interface is a device connected to a host or vro. Generally, a host has one interface while a vro has multiple interfaces. To make the interface work at the network layer, each interface must have an IP address. Therefore, the IP address is actually associated with the interface, rather than connected to the host or router. 1. An IPv4 address format IP address is a 32-bit binary number, which is usually divided into four "8-bit binary numbers" (4 bytes ). IP addresses are usually expressed in the form of (a. B. c. d), where, a, B, c, and d are all 0 ~ A decimal integer between 255. For example, the IP address 100.4.5.6 is actually a 32-bit binary number (01100100.00000100.00000101.00000110 ). On the Internet, each host or router interface has an IP address. However, the IP addresses of each interface cannot be selected at will. The components of the IP addresses of each interface must be determined by their connected subnets. 1. When classification addressing is initially designed to facilitate addressing and hierarchical network construction, each IP address consists of two ID codes (IDS), namely the network ID and host ID. All hosts on the same physical network use the same network ID. A host on the network (including Workstation, server, and router) has a host ID corresponding to it. The Internet Committee defines five IP address types to suit networks of different capacities, that is, Class ~ Class E. The, B, and C3 categories (as shown in the following table) are allocated by InternetNIC globally, and Class D and Class E are special addresses.
Maximum number of networks in the network category the first available network number the last available network number the maximum number of hosts in each network A126 (2 ^ 7-2) 112616777214B16384 (2 ^ 14) 128.0191.25565534C2097152 (2 ^ 21) 192.0.0223.255.255254 its address layout is as follows: Class a ip Address
A Class a ip address refers to the network number of the first segment of the four segments of the IP address, and the remaining three segments are the numbers of the local computer. If A binary IP address is used to represent an IP address, A Class a ip address consists of A 1-byte network address and A 3-byte host address. The maximum IP address must be 0 ". In Class a ip addresses, the network ID length is 8 bits, the host ID is 24 bits, and the number of class A network addresses is small. It can be used in large networks with hundreds of thousands of hosts.
Class a ip address ranges from 1.0.0.0 to 126.20.255 [2] (in binary format: 00000001 00000000 00000000 00000001-01111111 11111111 11111111 11111111 ). The last one is the broadcast address.
The subnet mask of A-type IP addresses is 255.0.0.0. the maximum number of hosts supported by each network is 256 to the power of 3-2 = 16777214.
Class B IP Address
A Class B IP address refers to a network number in the four segments of the IP address. If the IP address is expressed in binary format, the B-type IP address consists of a 2-byte network address and a 2-byte host address. The maximum IP address must be "10 ". In B type IP addresses, the network ID length is 16 bits, and the host ID is 16 bits. B type network addresses are suitable for medium-sized networks, each network can accommodate more than 60 thousand computers.
Class B IP address range: 128.0.0.0-191.255.255.255 [1] (in binary format: 10000000 00000000 00000000 20170001----10111111 11111111 11111111 11111110 ). The last one is the broadcast address.
The subnet mask of the B-type IP address is 255.0.0, and the maximum number of hosts supported by each network is 256 to the power of 2 = 65534
Class c ip Address
A Class c ip address refers to the network number in the four segments of the IP address, and the remaining segment is the number of the local computer. If the IP address is expressed in binary format, the class c ip address consists of a 3-byte network address and a 1-byte host address. The maximum network address must be 110 ". In a class c ip address, the network ID length is 24 bits, the host ID is 8 bits, and the number of class C network addresses is large, which is suitable for small-scale local networks, each network can contain up to 254 computers.
Class c ip address range: 192.0.0.0-223.255.255.255 [1] (Binary: 11000000 00000000 00000000 00000001-11011111 11111111 11111111 11111110 ).
The subnet mask of the class c ip address is 255.255.255.0, and the maximum number of hosts supported by each network is 256-2 = 254
Class d ip Address
Class D addresses are used as multicast addresses by IP addresses. Multicast provides IP addresses with the ability to forward data to a specific object.
The 28bits of class D addresses are used as multicast group numbers instead of other IDs. Multicast Group addresses include up to 4-bit multicast group numbers of 1110. They can usually be expressed as the dot decimal number, ranging from 224.0.0.0 to 239.20.255.
A host set that can receive data sent to a specific multicast group address is called a host group ). A host group can span multiple networks. Members in the Host group can join or leave the Host group at any time. There is no limit on the number of hosts in the Host group, and hosts that do not belong to a host group can send information to this group.
Some Multicast Group addresses are identified by IANA as well-known addresses. They are also treated as permanent host groups.
The IP address ("0.0.0.0") with each byte of the special website corresponding to the current host; the IP address ("255.255.255.255") with each byte of the IP address is the broadcast address of the current subnet; all Class e ip addresses starting with "llll0" are reserved for future and lab use. The IP address cannot start with "127" in decimal format. The numbers 127.0.0.1 to 127.255.255.255 in this type of address are used for loop testing. For example, 127.0.0.1 can represent the IP address of the local machine. http://127.0.0.1 "To test the Web server configured on the local machine. The first six-digit Group of the network ID cannot be set to "0", and "0" indicates the local network. 2. CIDR addressing the current address allocation policy is classless Inter-Domain Routing (CIDR ). CIDR eliminates the traditional concepts of Class A, Class B, and class C addresses and subnet division, so it can allocate IPv4 address spaces more effectively. In the classified addressing scheme, only three types of addresses A, B, and C are available. However, for some organizations, the size of the addresses may be between class B and class C. If Class C addresses are used, not enough, and the use of Class B addresses will lead to a waste of valuable address resources. This problem can be solved using the CIDR solution. In this addressing scheme, the IP address is divided into two parts: the network part and the host part, and has the Form a. B. c. d/x, where x indicates the number of bits in the first part. The first x bits are called the prefix of this address. The IP addresses of all devices in the Organization have this prefix. Therefore, for external routers, it only needs a route pointing to this prefix. When a data packet enters the internal network of the organization, the internal router forwards the data packet based on 32-x bits. CIDR blocks consecutive IP addresses with the same network prefix ". 2. Address Allocation Management 1. Although you know the IP address format, you cannot define your own IP Address at will. For a simple example, you cannot give your own place a name at will, and then let the courier company deliver the mail to you, the courier company does not know the information of your custom address. In order to obtain a valid IP address, the IP address must be recognized by a router on the Internet. Why is it a router? Because the vro determines how the datagram is routed and how it is forwarded, your host is connected to the network only when the vro can forward the datagram to your host. In this sense, vrouters play a core role in the Internet. In terms of the structure of the Internet, the user needs to obtain an IP address or address block from the ISP, and the ISP obtains the address block from its upper-level ISP. In the end, all the addresses come from ICANN, internet Name and number distribution organization. 2. Obtain the host address. The source and management method of the address are described above. However, the address is not actually allocated to the interface. Technically, you can assign an IP address to an interface either manually or dynamically. Dynamic configuration is more commonly used, because it is more flexible and convenient, and can reduce the burden on administrators. Dynamic configuration is implemented through DHCP, that is, the Dynamic Host Configuration Protocol. It can be used not only to obtain IP information, but also to obtain the subnet mask, the first vro, And the DNS server address. Therefore, it is also a very important and common protocol. 3. The private address ICANN only manages public addresses, and some other private addresses. Private address is a non-registered address, which is used internally by the Organization.
The following lists the reserved private addresses.
Class A 10.0.0.0 -- 10.255.255.255
Class B 172.16.0.0 -- 172.31.255.255
Class C 192.168.0.0 -- 192.168.255.2553.NAT and UPnP1.NAT Network Address Translation (NAT, Network Address Translation) are connected to the WAN technology and are private (retained) it is widely used in various Internet access methods and networks. The reason is simple. NAT not only perfectly solves the problem of insufficient lP addresses, but also effectively avoids attacks from outside the network and hides and protects computers inside the network. NAT automatically modifies the source IP address and destination IP address of the IP packet. The IP address verification is completed automatically during the NAT process. Some applications embed the source IP address into the data part of the IP Message. Therefore, you also need to modify the data part of the packet to match the source IP address that has been modified in the IP header. Otherwise, the application that embeds the IP address in the packet data cannot work normally. There are three NAT implementation methods: Static translation Static Nat, Dynamic translation Dynamic Nat, and port multiplexing OverLoad. Static conversion: it refers to converting the private IP address of the internal network to a public IP address. The IP address pair is one-to-one and remains unchanged. A private IP address is only converted to a public IP address. Static conversions allow external networks to access certain devices (such as servers) in the internal network. Dynamic conversion: when the private IP address of the internal network is converted to a public IP address, the IP address is random and uncertain, all private IP addresses authorized to access the Internet can be randomly converted to any specified legal IP address. That is to say, dynamic conversion can be performed as long as you specify which internal addresses can be converted and which legitimate addresses can be used as external addresses. Multiple valid external address sets can be used for dynamic conversion. When the valid IP addresses provided by the ISP are slightly less than the number of computers in the network. You can use a dynamic conversion method. Port address Translation (PAT): modifies the source Port of the outbound data packet and converts the Port, that is, Port Address Translation (PAT, Port address Translation ). port multiplexing is used. All hosts in the internal network can share a valid external IP address to access the Internet, thus saving IP Address resources to the maximum extent. At the same time, all hosts in the network can be hidden to effectively prevent attacks from the internet. Therefore, port multiplexing is the most widely used network. Either way, a NAT translation table is used internally, which records information about address translation. NAT is also controversial: it uses port numbers, which are designed to differentiate network programs. It makes the router have to process information above the network layer, in violation of the layered principle, it violates the end-to-end principle, that is, the host should communicate with each other directly. UPnPUPnP refers to generic plug-and-play, which can be used to support NAT traversal. It requires that the host and NAT are UPnP compatible. When using it, applications running on a host can request a NAT ing for the announcement port numbers of some requests, which are located at (private IP address, private port number) and (Public IP address, public port. If NAT accepts the request and claims the ing, the node from outside will be able to initiate a TCP connection (Public IP address, public port number. 3. ICMPICMP is an Internet Control Message Protocol. It is a sub-Protocol of the TCP/IP protocol family. It is used to transmit control messages between IP hosts and routers. A message control refers to a message of the network itself, such as network connectivity, host accessibility, and routing availability. Although these control messages do not transmit user data, they play an important role in transferring user data. ICMP is a network-layer protocol that provides consistent and easy-to-understand error report information. The error message sent is returned to the device that sends the original data, because only the device that sends the error message is the logic recipient of the error message. The sender can then determine the type of the Error Based on the ICMP message and determine how to better resend the failed data packet. However, the only function of ICMP is to report problems rather than correct errors. The task of correcting errors is completed by the sender. ICMP packets are classified into two categories: ICMP Query Packets and ICMP error packets. For ICMP error packets, ICMP packets always contain the first eight bytes of the IP datagram that is generated for the first time. In the following cases, ICMP error packets are not generated: ICMP error message. Is the IP datagram of the broadcast address or multicast address. As the datagram of link layer broadcast. It is not the first slice of an IP address. The source address is not a datagram of a single host. This means that the source address cannot be zero address, loop address, broadcast address, or multicast address. ICMP Query Packets are used to query network-related information, such as echo response and request (ping), router request and notification, and timestamp. 4. The IP address technology widely used in IPv6 is IPv4, which has some problems: Limitations of the address space: the crisis of the I P address space has been around for a long time and is the main driving force of the upgrade. Performance: Although I P performs well, some designs from 2 0 years ago or even earlier can be further improved. Security: security has always been considered to be the responsibility of the layer above the network layer, but it is now the role of the next version of the IP. Automatic Configuration: the configuration of I P v 4 nodes is always complicated, while the network administrator and users prefer "out-of-the-box", that is: plug the computer in the network and then start using it. Enhanced I P host mobility also requires better configuration support when hosts move across different networks and use different network access points. These problems are the driving force of IP upgrade. The next generation of IP technology room IP version 6 is IPv6. Compared with IPv4, IPv6 mainly includes extended addresses. The address is extended to 128 bits, and the address space is increased by 96 to the power of 2. Simplified the Header Format. There are only eight fields to accelerate packet forwarding and increase throughput. Enhanced support for extensions and options. It supports more services and simplifies packet forwarding. Stream tag. The router needs to track and maintain certain information, which remains unchanged in each packet in the stream. This method enables the router to efficiently process packets in streaming mode. Authentication and confidentiality. Identity Authentication and privacy are key features of IPV6. 1. Shows the IPv6 Header version. The length is 4 bits. for IPv6, this field must be 6. Category. The length is 8 bits, indicating that the package provides a "differentiated service ". This field is defined independently of IPv6 and has not been defined in any RFC. The default value of this field is all 0. Stream tag. It is a 20-bit package used to identify the same business flow. A node can serve as the sending source for multiple business flows at the same time. The stream tag and source node address uniquely identify a business flow. The net charge length. The length is 16 bits, including the bytes of the packet net load, that is, the number of bytes contained in the packet after the IPv6 Header. This means that the length of the IPv6 extension header is included in the calculation of the net Load Length. Next header. This field specifies the protocol type in the header field after the IPv6 Header. Similar to IPv6 fields, the next header field can be used to indicate whether the top layer is TCP or UDP, but it can also be used to specify the existence of IPv6 extension headers. Hop limit. The length is 8 bits. Each time a node forwards packets, this field is reduced by 1. If this field reaches 0, the package will be discarded. Source Address. The length is 128 characters, indicating the sender address of the IPv6 package. Destination Address. The length is 128 bits, indicating the receiver address of the IPv6 package. This address can be a unicast, multicast, or any on-demand address. If you use a routing extension header (which defines a special route that a packet must go through), the destination address can be the address of an intermediate node instead of the final address. Compared with IPv4, the header length does not exist because the IPv6 Header has a fixed length. The service type field is changed to the stream type. The datagram length is changed to the net charge length. The net charge length of IPv6 contains the extension header, while the IPv4 datagram length field specifies the length of the entire datagram, including the header. Therefore, in IPv4, the router needs to calculate the packet's Net Load Length by subtracting the datagram length from the packet header length, which is not required in IPv6. The datagram ID, identifier, and flag fields are deleted because they are used for datagram sharding in IPv4. However, IPv6 slice is implemented through the shard extension header and must be completed on the source device. The survival field is changed to the hop limit, and the usage similar to the protocol field is changed to the next header. The protocol field in v4 is used to indicate the high-level protocol type, but the next header can be used to indicate the extended header or the high-level protocol header. The header checksum is deleted. Because the header checksum is calculated for top-level protocols such as TCP and UDP, IPv4 header checksum is redundant, so this field has disappeared in IPv6. For apps that really need to authenticate the content, IPv6 provides the authentication header. The source object address has been extended to 128 bits. 2. Addressing 1. Address expression IPv6 address is 4 times longer than IPv4 address, and the complexity of expression is 4 times that of IPv4 address. The basic expression of an IPv6 address is X: X, where X is a 4-bit hexadecimal INTEGER (16 digits ). Each number contains four digits, each integer contains four digits, and each address contains eight integers, totaling 128 bits (4 × 4 × 8 = 128 ). For example, the following are some valid IPv6 addresses:
CDCD: 910A: 2222: 5498: 8475: 1111: 3900: 2020
1030: 0: 0: 0: C9B4: FF12: 48AA: 1A2B
2000: 0: 0: 0: 0: 0: 0: 1
Note that these integers are hexadecimal integers, with A to F representing 10 to 15. Each integer in the address must be expressed, but the starting 0 does not need to be expressed. This is a standard IPv6 address expression, and there are two more clear and easy-to-use methods.
Some IPv6 addresses may contain a long string of 0 (as in the second and third examples above ). In this case, the "gap" is allowed in the standard to indicate the 0 of this long string. In other words, the address
2000: 0: 0: 0: 0: 0: 0: 1
It can be expressed:
2000: 1
The two colons indicate that the address can be expanded to a complete 128-bit address. In this method, only when all the 16-bit groups are 0 will they be replaced by two colons, and the two colons can only appear once in the address.
There may be a third method in the hybrid environment of IPv4 and IPv6. The minimum 32 bits in an IPv6 address can be used to represent an IPv4 address, which can be expressed in a hybrid manner, that is, X: d. d. d. d, where X represents a 16-digit integer, while d represents an 8-digit decimal integer. For example, the address
0: 0: 0: 0: 0: 0: 10.0.0.1
Is a valid IPv4 address. Combine the two possible expressions. The address can also be expressed:
: 10.0.0.1
Because an IPv6 address is divided into two parts: the subnet prefix and interface identifier, it is expected that an IP node address can be expressed as an address carrying an additional value in a way similar to a CIDR address, the additional value indicates the number of bits in the address as the mask. That is, the IPv6 Node Address specifies the prefix length, which is differentiated from the IPv6 address by a slash. For example:
1030: 0: 0: 0: C9B4: FF12: 48AA: 1A2B/60
The prefix length used for routing in this address is 60 characters. Limit 6128 bit address space is divided:
2. The addressing model IPv6 addressing model is similar to IPv4. Each Unicast address identifies a separate network interface. An IP address is assigned to a network interface instead of a device. Therefore, a device with multiple network interfaces can have multiple IPv6 addresses. Any IPv6 address can represent the device. Although a network interface can be associated with multiple unicast addresses, one Unicast address can only be associated with one network interface. Each network interface must have at least one Unicast address.
Here is a very important statement and a very important exception. This statement is related to the use of point-to-point links. In IPv4, all network interfaces, including a point-to-point link connecting a device to a router (using many dial-up Internet connections), require a dedicated IP address. As many organizations start to use point-to-point links to connect their branches, each link requires its own subnet, which consumes a lot of address space. In IPv6, if any point-to-point link endpoint does not need to receive or send data from a non-neighbor device, they do not need a special address. That is, if two devices are mainly transmitting business flows, they do not need IPv6 addresses.
The requirement to assign a globally unique Unicast address to each network interface hinders the expansion of IPv4 addresses. A server that provides general services may crash in high demand. Therefore, an important exception is raised in the IPv6 address model: If the hardware can correctly share its network load on multiple network interfaces, then multiple network interfaces can share an IPv6 address. This makes it possible to expand from the server to the Server Load balancer cluster, instead of upgrading hardware when the demand for servers increases. 3. There are three types of IPv6 addresses: unicast, multicast, and any on-demand. The broadcast address is no longer valid. RFC 2373 defines three IPv6 address types: unicast: the identifier of a single interface. Packets sent to a unicast address are sent to the interface identified by this address. Pan-play: the identifier of a group of interfaces (generally different nodes. Packets sent to a wildcard IP address will be transmitted to one of the interfaces identified by this IP address (select the nearest one based on the distance calculation method of the routing protocol ). Multicast: the identifier of a group of interfaces (generally different nodes. Packets sent to a multicast address are transmitted to all interfaces with the address ID. 1. the unicast address identifies a separate IPv6 interface. A node can have multiple IPv6 network interfaces. Each interface must have a unicast address. A unicast address can be considered to contain a piece of information, which is contained in a 128-bit field. This address can completely define a specific interface. In addition, the data in the address can be interpreted as multiple segments. However, when all the information is put together, it will constitute a 128-bit address that identifies a node interface.
The IPv6 address itself can provide more or less information about the node's structure, depending on who will observe the address and what to observe. For example, a node simply needs to know that the entire 128-bit address is a globally unique identifier and does not need to know whether the node exists in the network. On the other hand, a vro can use this IP address to identify a unique node in a specific network or subnet. The IPv6 unicast address format defined in RFC 2373 is as follows: IPv6 unicast addresses include the following types: globally available addresses. No specified address or all 0 addresses. Return address. An IPv6 address with an IPv4 address. Supplier addresses based on suppliers and geographical locations. OSI Network Service Access Point (NSAP) address. IP address of the IP address. 2. multicast is used to identify a group of nodes. When a device subscribes to a multicast address, it declares that it wants to become a member of multicast. Therefore, any local router will reserve the multicast address in the name of this node. When other devices on the same network want to send information to the multicast address, IP multicast packets are encapsulated in the Link Layer Multicast Data Transmission unit. Send messages to devices concurrently. The format of an IPv6 multicast address is as follows: the multicast address can only be used as the destination address, and the multicast address is used as the source address without a datagram. The 1st bytes in the address format are all "1" and identify the multicast address. Multicast addresses account for IPv6
The total address space is 1/256. The rest of the multicast address format except 1st bytes, including the following three fields: the flag field consists of four individual bits. From left to right: the highest bit is the Reserved Bit and must be 0. If the R bit is set to 0, it indicates the multicast address of the non-embedded RP. If the R bit is set to 1, it indicates the multicast address of the embedded RP. In this case, the P and T bit must also be set to 1. P-Bit 0 indicates the multicast address not based on the unicast prefix; 1 indicates the multicast address based on the unicast prefix. At this time, the T-bit must also be set to 1. If the T-bit value is 0, the multicast address is permanently allocated. If the value is 1, the multicast address is not permanently allocated. Range field: 4-bit long, used to represent the multicast range. That is, multicast groups only include nodes in the same region network, the same site, and the same organization, or nodes at any location in the IPv6 global address space. The possible values of the four bits are 0 ~ 15. Group Identifier Field: 112 characters long, used to identify multicast groups. Depending on whether the multicast address is temporary, well-known, and the address range, the same multicast identifier can represent different groups. A permanent multicast address is a group identifier assigned with special meanings. The group members depend on both the group identifier and the range. Multicast range value and its significance
3. In a sense, multicast addresses can be shared by multiple nodes. All nodes of the multicast address Member are expected to receive all packets sent to the address. The wildcard IP address is similar to the multicast IP address. multiple nodes share one multicast IP address. The difference is that only one node is expected to receive the datagram from the wildcard IP address.
Wildcard play is particularly useful for providing certain types of services, especially for services that do not have a specific relationship between the client and the server, such as domain name servers and time servers. A name server is a name server and should work as well as far and away. Similarly, a near-time server is more desirable in terms of accuracy. Therefore, when a host sends a request to the Pan-play address to , the response should be the closest server associated with the Pan-play address.
1. Distribution and format of pan-play addresses
The wildcard IP address is allocated outside the normal IPv6 unicast IP address space. Because the unicast address and unicast address cannot be separated in form, each member of a wildcard address must be explicitly configured to identify the wildcard address.
2. a wildcard playback address must have an option: This option includes pointers pointing to the network interfaces of all nodes that share the wildcard address. This information will be used for router routing.