NFBPF_COMPILE(8)

✨ NFBPF_COMPILE ✨

okay bestie, welcome to the nfbpf_compile page 💅 this one lives in the iptables world (version 1.8.11, if you're keeping receipts) and it's genuinely such a useful little goblin. come sit, we're gonna get you fluent in it 🫶

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🌸 NAME 🌸

nfbpf_compile — generate bytecode for use with xt_bpf

like. it makes BPF bytecode. for xt_bpf. that's the whole job and she does it beautifully 😌

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🎀 SYNOPSIS 🎀

nfbpf_compile [ LLTYPE ] PROGRAM

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

so you can pass an LLTYPE, or you can just... not, and let her pick 🧚 either way PROGRAM is the main character here.

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💖 DESCRIPTION 💖

The nfbpf_compile utility aids in generating BPF byte code suitable for passing to the iptables bpf match. no cap — that's literally her entire purpose and she's obsessed with it ✨

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👑 OPTIONS 👑

• LLTYPE — the link-layer header type to operate on, bestie. it's a name as defined in <pcap/dlt.h>, but with the leading DLT_ prefix stripped off (yes, they really do just chop it off, iconic honestly). for use with iptables, RAW should be the right choice — it's also the default if not specified 🌈 so if you say nothing, she's already giving RAW.
• PROGRAM — the BPF expression to compile 🦋 peep pcap-filter(7) for a description of the language, because that's where the grammar lives.

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💀 EXIT STATUS 💀

The program returns 0 on success, 1 otherwise. so 0 is the slay, 1 is the "not me" 😭

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🍓 EXAMPLE 🍓

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

see how she just hands you the bytecode and you pipe it straight into --bytecode?? that's the vibe fr fr 🔥

The description of bpf match in iptables-extensions(8) lists a few more examples, so if you want more inspo, that's your next stop 📚

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🔥 SEE ALSO 🔥

• iptables-extensions(8)
• pcap-filter(7)

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and that's the whole page, bestie!! 💜 this was iptables 1.8.11's NFBPF_COMPILE(8) — go forth and compile some bytecode, you absolute main character 👑🦋