This tutorial explains three useful test scenarios to analyze slow networking issues. On a network slow network is a common issue. When this situation is encountered, the following questions should be asked.
1. Are you facing the issue when you are accessing a specific application ?
2. Are you facing the issue when you are accessing a specific system ?
3. Are you facing it when you are accessing internet ?
To analyze the first issue, use a protocol analyzer like wireshark on the system with the application. Apply a filter for the specific application . For ex, if the issue is with the FTP application apply a filter tcp.port==21 to filter all traffic corresponding to the FTP traffic. Check for TCP re transmissions, duplicate acks, timeouts etc. Also check the number of existing connections on the server for the specific application using tools like netstat.
To analyze the second issue, use a troubleshooting tool like ping and send about 100 packets to the server and analyze the number of packet drops. This would help to confirm issues related to network cards , duplex mismatches etc.
To analyze the third issue, check for DNS resolution times using custom scripts, and check for packet losses on the internet, which would help analyze issues with the internet service provider.