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The BSD Packet Filter: A New Architecture for User-level Packet Capture

The BSD Packet Filter: A New Architecture for User-level Packet Capture. Steven McCanne and Van Jacobson Lawrence Berkeley Laboratory Winter USENIX, December 19,1992. Introduction The BPF Network Tap The CSPF(Tree) Filter Model The BPF(CFG) Model The BPF Pseudo-Machine

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The BSD Packet Filter: A New Architecture for User-level Packet Capture

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  1. The BSD Packet Filter: A New Architecture for User-level Packet Capture Steven McCanne and Van Jacobson Lawrence Berkeley Laboratory Winter USENIX, December 19,1992 Shen Chuan-Hsing

  2. Introduction • The BPF Network Tap • The CSPF(Tree) Filter Model • The BPF(CFG) Model • The BPF Pseudo-Machine • Filter Performance Measurements • Conclusion Shen Chuan-Hsing

  3. Introduction • So What‘s A Packet Filter？ • Because network monitors run as user-level processes, packets must be copied across the kernel/user-space protection boundary. This copying can be minimized by deploying a kernel agent called a packet filter, which discards unwanted packets as early as possible. • Why Would I Want to Packet Filter？ • Control. Security. Watchfulness. Shen Chuan-Hsing

  4. The BPF Network Tap Shen Chuan-Hsing

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  7. The CSPF(Tree) Filter Model Shen Chuan-Hsing

  8. The BPF(CFG) Model Shen Chuan-Hsing

  9. The BPF Pseudo-Machine • This filter accepts all IP packets • ldh [12] • jeq #ETHERTYPE_IP, L1, L2 • L1: ret #TRUE • L2: ret #0 Shen Chuan-Hsing

  10. The BPF Pseudo-Machine (cont.) • This filter accepts all IP packets, beside 128.3.112 or 128.3.254. • ldh [12] • jeq #ETHERTYPE_IP, L1, L4 • L1: ld [26] • and #0xffffff00 • jeq #0x80037000, L4, L2 • L2: jeq #0x8003fe00, L4, L3 • L3: ret #TRUE • L4: ret #0 Shen Chuan-Hsing

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  14. Filter Performance Measurements Shen Chuan-Hsing

  15. Conclusion • Tcpdump: filter translation, packet acquisition, and packet display Shen Chuan-Hsing

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