NCC#2008053970 [ris-int] [Fwd: Quagga question]
Erik Romijn eromijn at ripe.net
Tue May 27 10:52:24 CEST 2008
Hi, we've never seen this problem, but we've never specifically looked for it either. I have been doing things with the dump code for ASN32, so I know some parts of it. Looking into the code briefly just now, the dumping of the packet seems to be done by bgp_dump_packet_func, which is called by bgp_dump_packet which is called by bgp_read (which processes incoming BGP packets). So, it would seem that the processing of the packet is done -after- the dump, but I'm not sure about it. If so, it could be that the BGP route handling in quagga actually switches the order around or has some other bug, and that the dump is correct. OTOH, the dump code is probably one of the least tested parts... I would suggest confirming with tcpdump whether the dumpfile is actually in the wrong order, to be sure that the bug is not actually in the BGP handling. However, I have no time to do this. But, as it may affect RIS, I'd like to know about any news :) cheers, Erik On May 27, 2008, at 10:18 AM, Henk Uijterwaal wrote: > Hi RIS team, > > See below. Any comments or ideas? > > Olaf helped with us on myASn in the past, so we should say a little > bit > more than just a standard answer. > > Henk > > > -------- Original Message -------- > Subject: Quagga question > Date: Tue, 27 May 2008 09:42:26 +0300 > From: Olaf Maennel <olaf at maennel.net> > To: Henk Uijterwaal <henk at ripe.net> > CC: Ashley Flavel <ashley.flavel at adelaide.edu.au> > > > Dear Henk, > > how are you? haven't heard from you for a while now... Hope > everything is > okay?! > > Ashley, one of my colleagues in Australia, was looking into errors > in quagga > and suspects that updates could sometimes be reordered if they > arrive within > a very short time (= not written to file in chronological order). > Are you > aware of anything like that? > > Thanks, > > olaf > > > > On 27/05/08 4:44 AM, "Ashley Flavel" <ashley.flavel at adelaide.edu.au> > wrote: >> Hi guys, >> I'm looking at making the CleanBGP stuff usable by others (including >> myself). Just found an interesting 'feature' of the data. I'm not >> sure if it is a bug in the Quagga route monitor collecting the data, >> but this is what is happening... >> If two updates are received at the same timestamp for the same >> prefix, >> I have been assuming that the ordering of them in the file dictates >> which order they were received in. However, this is not necessarily >> the case :( I have found cases where a prefix is updated twice in >> the >> same second and the ordering of the updates is incorrect in the files >> (I know this as I have tables which tell me the entry which is >> present). It gets worse... I have also found cases where updates >> with >> a gap of 1 second are recorded in the incorrect order. >> I have a way to deal with this... I keep a history of the last update >> prior to the current update (if it is within 5 seconds -- I could >> make >> this larger if I needed to). Then when I compare my constructed >> table >> at a timestamp, if a difference occurs, I can check if this is as a >> result of the ordering of 'almost simultaneous' updates. >> So... although this is annoying -- it also adds to the 'things you >> need to be careful about' when analysing the data. >> Ash > > > > > > -- > ------------------------------------------------------------------------------ > Henk Uijterwaal Email: > henk.uijterwaal(at)ripe.net > RIPE Network Coordination Centre http://www.amsterdamned.org/~henk > P.O.Box 10096 Singel 258 Phone: +31.20.5354414 > 1001 EB Amsterdam 1016 AB Amsterdam Fax: +31.20.5354445 > The Netherlands The Netherlands Mobile: +31.6.55861746 > ------------------------------------------------------------------------------ > > Is one of the choices leaving the office open? > Alan Greenspan on the next > elections > -- Erik Romijn RIPE NCC software engineer http://www.ripe.net/ Information Services dept.
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