Date: Mon, 12 Jun 2006 20:57:51 +0200 From: Ulrich Spoerlein <uspoerlein@gmail.com> To: Vadim Goncharov <vadim_nuclight@mail.ru> Cc: freebsd-isp@freebsd.org, freebsd-net@freebsd.org, freebsd-current@freebsd.org Subject: Re: [PATCH] ng_tag - new netgraph node, please test (L7 filtering possibility) Message-ID: <20060612185751.GB1226@roadrunner.aventurien.local> In-Reply-To: <opta09vodb17d6mn@nuclight.avtf.net> References: <optax2g7jq4fjv08@nuclight.avtf.net> <70e8236f0606110836j38f7ca33wa3058eaecf386fb5@mail.gmail.com> <optazz26kn17d6mn@nuclight.avtf.net> <d3ea75b30606111534q337aa27aj87baa1f20550ac1c@mail.gmail.com> <opta09vodb17d6mn@nuclight.avtf.net>
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[-- Attachment #1 --] Vadim Goncharov wrote: > I hope that my explanation was helpful enough to understand :) Also, if you will be using > 7.0, include BPF_JITTER in your kernel config as this will enable native code-compiling for > bpf and ng_bpf - this will speed things up. Am I the only one, that thinks BPF_JITTER is a stupid name? It suggest you add or enable jitter for the packet flow. No one wants jitter! It sucks. Why isn't it called simply BPF_JIT? Everyone knows what JIT stands for, JITTER on the other hand is to be avoided. > P.S. Here is quick-and-dirty primer how to convert ipp2p functions to ng_bpf(4) input > expression for tcpdump(1). Go to http://www.ipp2p.org/ and download source, unpack and open > file pt_ipp2p.c and find function for your P2P type, let it be BitTorrent for our example. So > look (I've formatted that bad Linux code a little to be a more style(9)'ish): > [snip] > We can give 1, 2 or 4 bytes to tcpdump for comarison at one time. The "payload" variable in > the source points to beginning of data in TCP packet. Remember from man ng_tag that tcpdump > assumes packets to have 14-byte Ethernet header for it's arrays like "tcp[]", but packets > come from ipfw to ng_bpf without this header, and that affects our offset calculations. So we > must give offsets from very beginning of packets, which is done through "ether[]" tcpdump's > prime, and parse headers manually. Let's assume (for simplicity and speed), however, that IP > and TCP headers have no any options and thus always have length 20 bytes each, then ipp2p's > "payload[0]" will be tcpdump's "ether[40]". Also, let's assume that ipfw checked packet len > for us so we don't do that in netgraph too. > > Then, we simply take hex bytes in order hd(1) told us, as this is network byte order also, > and write them as tcpdump expressions (remember that first string ("...protocol") actually > have 0x13 prepended to it). So, we write follow in ng_bpf(4) script: > [snip] > Note the last OR block in expression - this is translation of that "not sure" checking > request packets. I've explicitly written packet length - plen=17 + 20 byte IP header len + 20 > byte TCP header len, check at offset 2 in IP header, according to RFC 791. Construction > "get_u32 == __constant_htonl()" means comparing 4-byte values at given offset. Great stuff, this should make it somewhere into /usr/share/examples! Ulrich Spoerlein -- PGP Key ID: 20FEE9DD Encrypted mail welcome! Fingerprint: AEC9 AF5E 01AC 4EE1 8F70 6CBD E76E 2227 20FE E9DD Which is worse: ignorance or apathy? Don't know. Don't care. [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (FreeBSD) iD8DBQFEjbkv524iJyD+6d0RAsCmAJ9TnrhmRItXr/duWMSv2sIkdq6NVgCgmA9S EWI/jDS2ECluq4ww7LT7k6I= =YXjO -----END PGP SIGNATURE-----
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