Match using Linux Socket Filter. Expects a BPF program in decimal format. This is the format generated by the nfbpf_compile utility.

--bytecode code
    Pass the BPF byte code format (described in the example below).

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

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