To allow for packet capturing, DrayTek routers have a Port Mirroring facility, which assigns one port to receive data from other LAN or WAN ports on the router.
When working with a router on-site, it is a great way to diagnose and troubleshoot networking issues. Simply plug in a PC running Wireshark to the Port Mirror port to capture packets and diagnose network issues.
When working with a router remotely, instead of being on-site, packet capturing can be much more difficult. The Vigor 3910 provides a Web UI Packet Capture facility to remotely capture packets from the router’s LAN or WAN interfaces and save them as a .pcap file to help with diagnosing network issues.

This article depicts setup steps of the build-in packet capture feature available on Vigor 3910 routers.

Step 1.
Go to [Diagnostics] > [Port Mirror/Packet Capture],

1. select Download .pcap
2. choose desired WAN or LAN interfaces

Step 2.
Choose the relevant Setting option:

1. Capture All Packets option saves traffic for selected interfaces for 60 seconds by default. This can be set to 30, 120, 180, 300, or 600 seconds. Press Start to begin the packet capture process.



2. Capture with Filter option defines filters such as ICMP, TCP, UDP, or TCP/UDP Protocols, an IP Address, or a Port Number. Press Start to begin the packet capture process.

Step 3.
The packet capture process can be interrupted at any time. The maximum size of the packet capture file is 200MB. Packet capturing will finish at the end of the specified capture duration, or when the capture file reaches 200MB in size. Press the Stop button to end the capture immediately.

Step 4.
Once the capture is completed, the Status will change from Capturing to Idle. The packet capture file is ready. Press Download to save it on your computer.

Step 5.
Downloaded packet capture file is saved as pkt_monitor.pcap by default. Once opened in your favourite application (we have used Wireshark here), packets can be inspected.

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