Date: Thu, 03 Mar 2005 10:42:53 -0800 From: "Bruce A. Mah" <bmah@freebsd.org> To: Brooks Davis <brooks@one-eyed-alien.net> Cc: cvs-src@freebsd.org Subject: Re: cvs commit: src/sys/netgraph/netflow netflow.c Message-ID: <1109875373.752.30.camel@localhost> In-Reply-To: <20050303173852.GC4737@odin.ac.hmc.edu> References: <200503031101.j23B16Vn065793@repoman.freebsd.org> <20050303173852.GC4737@odin.ac.hmc.edu>
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--=-Q+EcZfUKptIVzfOBHX8T Content-Type: text/plain Content-Transfer-Encoding: quoted-printable If memory serves me right, Brooks Davis wrote: > On Thu, Mar 03, 2005 at 11:01:06AM +0000, Gleb Smirnoff wrote: > > glebius 2005-03-03 11:01:06 UTC > >=20 > > FreeBSD src repository > >=20 > > Modified files: > > sys/netgraph/netflow netflow.c=20 > > Log: > > Cisco uses milliseconds for uptime. This is stupid. Nobody cares of s= uch > > precision when IP packet may travel through internet for several seco= nds. > > Also uptime measured in milliseconds overflows every 48+ days. > > But we have to do same to keep compatibility with Cisco and flow-tool= s. > > =20 > > Make a macro MILLIUPTIME, which does overflowable multiplication to 1= 000. >=20 > JFYI, I know of applications that care about even higher granularity. > For instance, I talked to one of the people from Panasas this fall who > would really like the kernel timer interface to be able to handle > sub-millisecond timeouts. In their environment, at packet that has not > been acked in around 100 microseconds has been dropped! What's also odd is that NetFlow (at least the versions I work with) timestamps the export packets with nanosecond precision, then uses the "uptime-in-milliseconds" timestamp for both the packet and the individual NetFlow records. You have to do some weird arithmetic to get the "real" timestamps of the NetFlow records. (And if you have only millisecond precision offsets for the individual records, what's the point of nanosecond precision for the whole clump of them?) (This of course does not address the *accuracy* of the measurements which is a whole 'nother story.) Bruce. --=-Q+EcZfUKptIVzfOBHX8T Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.0 (FreeBSD) iD8DBQBCJ1qt2MoxcVugUsMRApYlAJ4yR2mJh+BgQ4jrueVjbdiQoqZOZQCfbM7c KZYJhkMlaG2XYUJoqAs8xTY= =wg5s -----END PGP SIGNATURE----- --=-Q+EcZfUKptIVzfOBHX8T--
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