Access point movie goes whizzing past very quickly as Bill Fenner narrates. Lets you see where people are congregating, and which talks are more interesting, and when people migrate out of talks; could feed into the survey to tell the program comittee which talks are of more interesting. netdisco, collects data from network elements, plots them, put a front end on it; If you opted in, by emailing him you MAC address, it would render a map with your location on it. has RSS feeds of your location as well. fenner at research.att.net 2006.02.15 An Inter-domain Consistency Management Layer Nate Kushman, MIT Steve Feldman, welcome back, Nate Kushman is up first to talk about routing consistency. Transient BGP loops was with akamai, now at MIT srikanth kandula, dina katabi, john wroclawski Do loops matter? can we do something about them? what is a transient BGP loop? slide showing loop forming. How common are "transient BGP loops" Sprint study, IMC 2003, IMW 2002 looked at packet traces from the sprint backbone up to 90% of the observed packet loss was caused by routing loops 60-100% could be attributed to BGP Is it true on internet? Routing loop damage 20 fvantage points with BGP feeds did pings, traceroutes, watch for loops. correlated on BGP updates, and ttl exceeded on ping, traceroute. In fact, all loops were within 100seconds of BGP updates. 10-15% of all BGP updates caused routing loops!! Collateral damage. they cause impacts on congestions that are part of the loop, causing loss to non-rerouted networks from non-rerouted-to source networks. traceroute to see which links were part of the loop, see which other traces shared a link in common with the loop. there is a marked increase in packet loss in the 100second window around the BGP loop. Prefixes sharing a loopy link see 19% packet loss in general. What should be done? We need to prevent forwarding loops. A loop occurs because: one AS pushes a route update to the data plane, but other ASes are not yet aware of that route change. What about telling everyone about the change before the change actually happens? Suspension: continue to route traffic tell control system not to propagate the route FIB stays same for now, RIB doesn't send route. downstream networks only update forwarding tables once upstreams have acknowledged the path change. More generally: we have proven: loops are prevented in general case convergence properties similar to normal BGP http://nsm.lcs.mit.edu/~nkushman/ incrementally deployable. feedback Clearly: works well for planned maintenace. We can delay move to backup path during those events, at least. 20% of update events caused by planned maintenance Link up events also cause loops, no way to plan for them smoothly now. What about: unplanned link down events trade-off between loss on current path and collateral damage Are we willing to do this in general, to avoid impacting stable prefixes from unstable prefixes. In short: routing loops are a significant performance concern. Bill Norton--hidden question: what is the time domain during which these traffic impacts are seen? Will the propagation path take 10, 20, 30 seconds? A. one event causes many, many loops rippling out, so one update may cause packet loss for many seconds, up to tens of seconds total. Q. you're talking about adding MORE state information into the network. Also adding latency to update acknowledgements. Jared notes that router software bugs tend to exacerbate routing loop issues. You can tune configs to try to minimize the number of loops seen, as well as upgrading to "fixed" code to get better results without more state. Patrick Gilmore asks jared, does tuning help internal sessions or external sessions? Both, it really controls *when* the updates are sent out (immediately vs batched, etc.). Jared notes the internet is being used Someone (Bill?) asks if convergence times are similar to current model, as the slide claims; is that within a few seconds? convergence in the lab is similar, yes. Matt Petach asks about details of convergence; it basically puts you at mercy of the slowest, farthest away router on the network, since it has to get the message, realize it has nobody to send to, and then acknowledge back before anyone else can update FIB; yes, true, so you'd want to put timers in to limit how long you wait; basically, like "wait 5 seconds, and either hear an ACK, or go ahead and update FIB" type timeout, so you don't wait forever for a non-conformant device on the other side of the world. Riverdomain question--with suspension, you're basically in passive mode, listening but not updating, is that correct? Yes, with respect to the links/prefixes in question.