powered by Caper
authored by Hyunsuk Bang
Welcome to bpfsimulator.com, your go-to playground for exploring the fascinating world of BPF (Berkeley Packet Filter) through intuitive graphical representations.
Simply type pcap expressions you want to compile into BPF, specify a pcap file to process, and check the 'optimized' box if you want to optimize the BPF.
See the example! EXAMPLE
BPF, short for Berkeley Packet Filter, has been a powerful tool for analyzing network traffic since its inception in 1992. Utilizing its own instruction sets and registers, BPF efficiently captures incoming packets by generating a control flow graph. This technique is employed by renowned tools such as tcpdump and libpcap to capture packets based on higher-level filter expressions known as 'pcap expressions.' These expressions are then transformed into BPF code to effectively process network data.
Curious to see how BPF code looks? You can easily inspect it by typing a simple command. Here's an example:
$ tcpdump -d "tcp or udp"
(000) ldh [12]
(001) jeq #0x86dd jt 2 jf 7
(002) ldb [20]
(003) jeq #0x6 jt 11 jf 4
(004) jeq #0x2c jt 5 jf 10
(005) ldb [54]
(006) jeq #0x6 jt 11 jf 10
(007) jeq #0x800 jt 8 jf 12
(008) ldb [23]
(009) jeq #0x6 jt 11 jf 10
(010) jeq #0x11 jt 11 jf 12
(011) ret #1514
(012) ret #0
These BPF codes, depending on the operating system, are either being interpreted by a virtual machine or compiled into machine code by a just-in-time compiler and executed in the kernel.
Thorough explanations of BPF can be found in the original paper, The BSD Packet Filter.
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