NFBPF_COMPILE(8) iptables 1.8.7 NFBPF_COMPILE(8)

nfbpf_compile - generate bytecode for use with xt_bpf

nfbpf_compile [ LLTYPE ] PROGRAM

LLTYPE := { EN10MB | RAW | SLIP | ... }

The nfbpf_compile utility aids in generating BPF byte code suitable for passing to the iptables bpf match.

Link-layer header type to operate on. This is a name as defined in <pcap/dlt.h> but with the leading DLT_ prefix stripped. For use with iptables, RAW should be the right choice (it's also the default if not specified).
The BPF expression to compile, see pcap-filter(7) for a description of the language.

The program returns 0 on success, 1 otherwise.

Match incoming TCP packets with size bigger than 100 bytes:

bpf=$(nfbpf_compile 'tcp and greater 100')
iptables -A INPUT -m bpf --bytecode "$bpf" -j ACCEPT

The description of bpf match in iptables-extensions(8) lists a few more examples.

iptables-extensions(8), pcap-filter(7)
iptables 1.8.7