Cause Analysis of Intranet server access failures over the Internet (Internet is acceptable)

The environment is as follows:

Internet IP Address: 218.94.2.20.

Lan: host a 192.168.1.100 host B 192.168.1.101
Machine A acts as a server and provides a Web service through port 88. Port 88 is also configured on the router to map to machine.

Server B serves as a general Intranet client.

 

Now:

The browser on B accesses the Web Service 222.188.91.252: 88 on a through the Internet IP address. The router forwards the IP address to server a through port ing. At this time, the IP address received by server a is 192.168.1.101, the protocol they use is TCP. TCP requires three handshakes to establish a connection. At this time, server a receives a connection request and replies to a response packet. The destination IP address is 192.168.1.101 and the source IP address is 192.168.1.100, because both IP addresses are in the LAN, routers directly forward the IP addresses without being encapsulated.

Therefore, the source IP address of the response packet received by server B is different from the destination IP address of the Request Packet sent by server B, so the packet is discarded.

Server A has been waiting for server B to respond again, but server B has discarded the package, so it cannot wait until the connection fails.