BPF (Berkeley Packet Filter)
Definition
A kernel-level packet filtering mechanism used by tcpdump, Wireshark, and most capture tools to select which packets are written to disk. BPF expressions such as 'port 443' or 'host 10.0.0.1' reduce capture file size and focus collection on relevant traffic. The filter runs in the kernel before packets reach user space, minimising CPU load.
Related terms
- Network Tap
- A hardware device inserted inline in a network cable path that passively copies the electrical or optical signal to one or more...
- Promiscuous Mode
- A network interface operating mode in which the card passes all received frames to the capture software, not just frames addressed to...
- JA3 / JA3S
- An MD5 fingerprint of the ordered fields of a TLS Client Hello (JA3) or Server Hello (JA3S). Allows identification of client software...
- Monitor Mode
- An 802.11 radio mode that captures every wireless frame in range, including management and control frames, without associating to an access point....
- PCAP / PCAPng
- The standard file formats for storing captured packets. PCAP (libpcap format) is the legacy standard supported by virtually all tools. PCAPng (Next...
- PCAPng
- PCAP Next Generation file format. Block-structured (SHB, IDB, EPB, ISB, DSB), supports multiple interfaces in one file, per-packet comments, name resolution, and...
- Ring Buffer Capture
- A capture mode in which the tool writes successive PCAP files of a fixed size or duration, overwriting the oldest when the...
- SPAN Port (Port Mirroring)
- A switch feature that copies frames from one or more source ports or VLANs to a designated destination port, where a capture...
Explained in these topics
- Live Packet Capture, Traffic Analysis and Deep Packet InspectionThe kernel-level filter language used by libpcap, tcpdump, Wireshark capture filters, Zeek and many flow exporters. Operates before the packet hits user space,...
- Packet Capture Tools and MethodsA kernel-level packet filtering mechanism used by tcpdump, Wireshark, and most capture tools to select which packets are written to disk. BPF expressions such...