Does the IP address will reset the connection of TCP?

Problem Description

Network communication generally needs to obtain the IP address of the other device, but what if the IP address changes during the connection process?

This question is very technical and representative, and it is worth discussing carefully.

IP address changes are nothing more than manual configuration changes and automatic configuration changes. Communication is good, no user will manually modify their IP. However, if the user has to modify the IP, there is nothing. Before the modification is successful, the operating system will reset the current connection, then modify the IP, and then reconnect after the modification is completed.

Automatic configuration

The automatic configuration here refers to the IP dynamically obtained through DHCP. The IP address is leased. The lease period is generally 8 hours. It can be used until the lease expires. In order to keep the communication smooth, the client usually starts a lease extension dialogue with the DHCP server when the lease period is still half of the lease. Under normal circumstances, the lease renewal is successful. As long as the lease renewal is successful, the IP address can be used normally.

Of course, if the DHCP server keeps the IP and does not renew the lease when it renews the lease, then the user will not renew the lease and the client will continue to use the original IP to continue communication. Then renew the lease before the IP lease expires. If it still fails, it will give up the original IP and receive the new IP assignment from the DHCP server. Since the IP address has changed, the TCP connection must be reset, and then a new TCP connection is established.

Wireless client

When the wireless client is moving, unbind from one AP and then bind to another AP, which may cause the original IP to be unusable. It must receive the new IP assigned by the new AP, which will also cause TCP connection. Reset.

Even if the old AP and the new AP are assigned the same IP network segment, the IP address assigned to the client is exactly the same. Although the IP address of the client has not changed, but because the bound AP has changed, the professional belongs to the "anchor location" "Changed", communication with the Internet because the NAT entry does not exist, causing a reset of the communication.

Through the above introduction, you will find that if you want to maintain a continuous TCP connection, you need to meet two conditions at the same time:

• Host IP unchanged

• The anchor point (Anchor Point) of the host on the Internet should also remain unchanged

As long as the above two conditions are met, no matter where the mobile client moves, whether it is using WiFi or using a mobile 4G network, this conclusion is all established!

What is an anchor?

In layman's terms, the anchor point is the combination of the "public IP + port number" that this mobile client presents on the Internet. The server has always thought that it is communicating with the anchor point. Reset connection.

Host IP unchanged

The host IP remains the same, the host will not be full, go to Reset the current connection. Only if there is a change, it will reset the current connection.

How to achieve it?

It is easy to realize that the host IP remains unchanged. Generally, the host will retain its current IP when roaming, so you can keep it. The wireless network says that since you like it, then you can continue to use it. However, unfortunately, the host has moved to another anchor, at least the public IP must be different from the original one.

solution

Establish a tunnel between the new anchor point and the old anchor point to tunnel all the roaming host traffic to the old anchor point. The old anchor point then extracts the traffic in the tunnel and uses the old anchor key information IP + port number) replace the private IP + port number of the host, and finally send traffic to the Internet, and finally reach the server.

The above is the news sharing from the PASSHOT. I hope it can be inspired you. If you think today' s content is not too bad, you are welcome to share it with other friends. There are more latest Linux dumps, CCNA 200-301 dumps, CCNP Written dumps and CCIE Written dumps waiting for you.