Topology: Server---Private network---AR28-11------Public network----PC
Symptom: PC in public network could access the server for private network through FTP, but it cannot open the directory, failing to download the file on server.
1. According to the configurations of AR28-11, AR28-11 has advertised the FTP of server in private network to public network, with configurations as follows:
nat server protocol tcp global X.X.160.100 inside 10.110.10.1 ftp
The command above could advertise both TCP20 and 21 ports of the server to public network.
2. Advertise the FTP configurations of server in private network at AR28-11, changing the configurations as follows:
nat server protocol tcp global X.X.160.100 inside 10.110.10.1 any
After the change, PC in public network could access the server in private network through FTP, and download the files normally.
3. Use display ip faster cache command to check the fast FIB of AR28-11, and it is found that the server does not use the port 20 stated in FTP to transmit files, but uses other else ports, so PC in public network cannot download the file on server in private network under AR28-11.
1. NAT server of AR28-11 is problematic in configuration, failing to advertise the FTP to public network.
2. The server does not use the port 20 of TCP to transmit files.
For the software that uses TCP20 port stipulated in standard FTP protocol to transmit files, it has to configure the port with mapping for thorough advertising of the port. Execute display ip fast cach command to check which ports are used to forward packets.