Match using Linux Socket Filter. Expects a path to an eBPF object or a cBPF program in decimal format.

--object-pinned path
    Pass a path to a pinned eBPF object.

Applications load eBPF programs into the kernel with the bpf() system call and BPF_PROG_LOAD command and can pin them in a virtual filesystem with BPF_OBJ_PIN. To use a pinned object in iptables, mount the bpf filesystem using

    mount -t bpf bpf ${BPF_MOUNT}

then insert the filter in iptables by path:

    iptables -A OUTPUT -m bpf --object-pinned ${BPF_MOUNT}/{PINNED_PATH} -j ACCEPT

--bytecode code
    Pass the BPF byte code format as generated by the nfbpf_compile utility.

The code format is similar to the output of the tcpdump -ddd command: one line that stores the number of instructions, followed by one line for each instruction. Instruction lines follow the pattern 'u16 u8 u8 u32' in decimal notation. Fields encode the operation, jump offset if true, jump offset if false and generic multiuse field 'K'. Comments are not supported.

For example, to read only packets matching 'ip proto 6', insert the following, without the comments or trailing whitespace:

    4 # number of instructions
    48 0 0 9 # load byte ip->proto
    21 0 1 6 # jump equal IPPROTO_TCP
    6 0 0 1 # return pass (non-zero)
    6 0 0 0 # return fail (zero)

You can pass this filter to the bpf match with the following command:

    iptables -A OUTPUT -m bpf --bytecode '4,48 0 0 9,21 0 1 6,6 0 0 1,6 0 0 0' -j ACCEPT

Or instead, you can invoke the nfbpf_compile utility.

    iptables -A OUTPUT -m bpf --bytecode "`nfbpf_compile RAW 'ip proto 6'`" -j ACCEPT

Or use tcpdump -ddd. In that case, generate BPF targeting a device with the same data link type as the xtables match. Iptables passes packets from the network layer up, without mac layer. Select a device with data link type RAW, such as a tun device:

    ip tuntap add tun0 mode tun
    ip link set tun0 up
    tcpdump -ddd -i tun0 ip proto 6

See tcpdump -L -i $dev for a list of known data link types for a given device.

You may want to learn more about BPF from FreeBSD's bpf(4) manpage.