directory

  • An overview of the
  • The physical layer
  • Data link layer
  • Network layer (1) Basic knowledge
  • Network layer (2) IP address design and exhaustion
  • Network layer (3) Network layer packet transmission process
  • Network layer (4) Network layer multicast and other applications
  • Transport layer (1) Reliable transport and TCP/UDP
  • Transport layer (2) congestion control and handshake waving

IP multicast

A one-to-many relationship when a piece of data needs to travel from one starting point to multiple ends. If one-to-one transmission is used, the same data needs to be sent many times, both for the volume of data and transmission efficiency is extremely low. But with IP multicast, it is sent only once. Multiple copies are copied by the router for transmission to multiple destinations. Once you reach the LAN, you can also use the LAN’s native multicast capabilities. That is, if the host is connected to the Internet via a LAN (most are).

How do you mark the beginning and the end

The intuitive idea is to write all the destination addresses of IP packets, but this is not realistic. Because there may be hundreds of destination addresses. You can mark the group with an address, and the class D address is a multicast address. A multicast address can only be used to mark a destination address. In addition, the PING command does not respond to ICMP error packets.

How to transfer

Now that you have the transmission format, how does the router know how to transmit and deliver to the host in the group? Two protocols are used, one is the multicast routing protocol for transmission between routers, and the other is the Internet management protocol IGMP for direct delivery by multicast routers. The multicast routing protocol is complicated, so you can learn it by yourself. Introduce the IGMP

Internet management protocol IGMP

Its function is to see if the host that the router is connected to participates in the multicast group. Procedure: 1. When a host joins a multicast group, it sends an IGMP packet to the multicast router to declare that it is a member of the multicast group. The multicast router also needs to check periodically whether the members of the group are still in the group, so it needs to search for each host. If there is no response, it indicates that the group is out.

You can see that the sender of a multicast group does not know how many members it has.

Virtual private network Vp.n

A unit can apply for a limited number of IP addresses, and some hosts are not connected to the Internet due to security issues. But these hosts need to communicate with other hosts on the LAN. They can assign IP addresses by themselves, but such local IP addresses conflict with global addresses on the network. When the network is running, IP addresses are not unique and problems can occur. That’s why a dedicated address is designated for internal communication within the organization. The router receives these addresses and does not forward them. Networks that use such addresses are called private networks. You can see that this address can be reused. In one case, hosts in the network need to link to other computers in remote locations. There are two kinds of distribution can be used, one is to rent a special line, simple answer is convenient, the cost is high, the other is to use the Internet as a carrier of communication, such communication is VP.N, virtual private network. The effect is the same as a real dedicated line, but not dedicated.

The VP. N

If it’s going through the Internet, it has to be a legitimate global IP address.

  1. The transmitted datagrams need to be encrypted, and the destination address is the global IP address of the remote
  2. The router encrypts the data when it realizes it has to go over the Internet
  3. Change the wish address to the router’s global IP address
  4. The destination router decrypts the packet after receiving it. Restore data and the destination local IP address. To complete the delivery

This way, as if over a dedicated network transmission. The whole process can be a tunnel. There is also a type of VP.N, or remote access, where remote employees need to connect to the company’s network, use the company’s services, conduct meetings, etc. The vP.n tunnel is established through the vP.n software and the company’s mainframe.

Network address translation NAT

This protocol is used on hosts that use local addresses to connect to the Internet. The intuitive way is to apply for additional IP addresses and assign them to him. But there are limitations to this reality. The fastest way is to use address translation NAT. A NAT router has a valid global IP address that an online host can use to transmit network data. 1. After receiving a request from an internal host to other hosts on the Internet, the internal host changes the source IP address to its own global IP address. 2. When network data is returned, NAT uses a translation table to map the data to a real local IP address for delivery. This network cannot be used as a server. Why? Because the NAT does not know who to deliver the data to. If there is only one IP address, you can only wait for queuing use, but now generally add a port number, you can share an IP address.