![]() ![]() Kernel-mode interpreters for that same virtual machine language are used in raw data link layer mechanisms in other operating systems, such as Tru64 Unix, and for socket filters in the Linux kernel and in the WinPcap and Npcap packet capture mechanism. Linux includes a BPF JIT compiler which is disabled by default. Some platforms, including FreeBSD, NetBSD, and WinPcap, use a just-in-time (JIT) compiler to convert BPF instructions into native code in order to improve performance. Some projects use BPF instruction sets or execution techniques different from the originals. This is accomplished using preprocessor conditions. Traditional Unix-like BPF implementations can be used in userspace, despite being written for kernel-space. Programs in that language can fetch data from the packet, perform arithmetic operations on data from the packet, and compare the results against constants or against data in the packet or test bits in the results, accepting or rejecting the packet based on the results of those tests.īPF is often extended by "overloading" the load (ld) and store (str) instructions. Filtering īPF's filtering capabilities are implemented as an interpreter for a machine language for the BPF virtual machine, a 32-bit machine with fixed-length instructions, one accumulator, and one index register. While one copy remains in the receipt path for user processes, this preserves the independence of different BPF device consumers, as well as allowing the packing of headers into the BPF buffer rather than copying complete packet data. In 2007, Robert Watson and Christian Peron added zero-copy buffer extensions to the BPF implementation in the FreeBSD operating system, allowing kernel packet capture in the device driver interrupt handler to write directly to user process memory in order to avoid the requirement for two copies for all packet data received via the BPF device. īPF provides pseudo-devices that can be bound to a network interface reads from the device will read buffers full of packets received on the network interface, and writes to the device will inject packets on the network interface. eBPF is also available for Microsoft Windows. The Linux kernel provides an extended version of the BPF filtering mechanism, called eBPF, which uses a JIT mechanism, and which is used for packet filtering, as well as for other purposes in the kernel. The BPF filtering mechanism is available on most Unix-like operating systems. Some systems, such as Linux and Tru64 UNIX, provide a raw interface to the data link layer other than the BPF raw interface but use the BPF filtering mechanisms for that raw interface. The filter program is in the form of instructions for a virtual machine, which are interpreted, or compiled into machine code by a just-in-time (JIT) mechanism and executed, in the kernel.īPF is sometimes used to refer to just the filtering mechanism, rather than to the entire interface. This avoids copying unwanted packets from the operating system kernel to the process, greatly improving performance. BPF returns only packets that pass the filter that the process supplies. For example, a tcpdump process may want to receive only packets that initiate a TCP connection. ![]() In addition, if the driver for the network interface supports promiscuous mode, it allows the interface to be put into that mode so that all packets on the network can be received, even those destined to other hosts.īPF supports filtering packets, allowing a userspace process to supply a filter program that specifies which packets it wants to receive. It provides a raw interface to data link layers, permitting raw link-layer packets to be sent and received. The Berkeley Packet Filter ( BPF) is a technology used in certain computer operating systems for programs that need to, among other things, analyze network traffic. Unix-like ( FreeBSD, OpenBSD, NetBSD, DragonFly BSD, macOS, Oracle Solaris 11 and later, AIX, Tru64, Linux, Orbis), Windows Interface to data link layers on a Unix-like system Berkeley Packet Filter Developer(s) ![]()
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