Thanks very much for the detailed info, Peter！ And the part of involving virtual entities into topology is even more interesting. Thanks！
Best, Bibo 在 2012-6-5 中午12:20，"Peter Phaal" <peter.ph...@inmon.com>写道： > Hi All, > > The original question was about L2 topology discovery. One of the > differences between sFlow and NetFlow is that sFlow operates at layer 2 > (reporting layer 2 interfaces and MAC addresses) and NetFlow typically > operates at layer 3 (reporting router (VLAN) interfaces and IP addresses). > Consequently, inferring L2 topology from sFlow data is much easier than > using NetFlow. > > As Robin pointed out, topology inference is a function of the > sFlow/NetFlow collector. Inferring L2 topology from sFlow involves > examining the sampled packet headers and forwarding paths reported by all > the switches in the network, see: > > http://blog.sflow.com/2009/05/packet-paths.html > > Installing Host sFlow on the hypervisor ( > http://host-sflow.sourceforge.net/) helps topology discovery by exporting > virtual machine information (UUID, hostname, MAC addresses) that can be > joined with sFlow data from OVS to identify which vNICs are associated with > each VM. > > Linking the virtual and physical topology topology gets interesting if you > use tunneling (GRE, VxLAN etc), but it is possible for an sFlow analyzer to > tie the layers together based on sFlow data: > > http://blog.sflow.com/2012/05/tunnels.html > > There is an inherent limitation in using traffic data to map topology - > you can only see links that carry traffic. However, even backup links carry > some traffic (STP, LLDP etc.) so it generally isn't much of a problem. > > Regards, > Peter > > On Jun 4, 2012, at 7:50 PM, Motonori Shindo wrote: > > Kim and Robin, > > NetFlow and sFlow can give you some idea how your network topology looks > like, but it is difficult to draw a complete picture of the network with > NetFlow/sFlow because they are not designed to do such a thing. > > Theoretically NetFlow and sFlow can tell on which interface a particular > flow traverses in the network and hence allows us to deduce the network > topology from there. In order to do so, however, NetFlow/sFlow collector > would have to correlate one flow record exported by one device to another > flow record exported by another device. This is extremely difficult to do > when there's a massive amount of flows in the network (and it is often the > case). In some case (but it is not the case for OVS though), flow is > "sampled" (meaning that not all packet are collected to generate flow > records) and it makes topology discovery by NetFlow/sFlow even more > difficult. > > Regards, > > --- > Motonori Shindo > > On 2012/06/05, at 2:41, Robin Wang wrote: > > Hi Kim, > > > I found an email that indicates OVS doesn't have built-in support. But it > was a year ago, not sure whether it's supported now. > > http://openvswitch.org/pipermail/discuss/2011-July/005400.html > > > For sFlow, to me, it is similar to NetFlow, and usually used to track > dynamic traffic in a network with the help of flow collector. There're lots > of different collectors. What you can get through sFlow depends on what > features the collector provides, not OVS. Not sure if there's a collector > provides topology things. Maybe someone who is familiar with collector > could give us some advice. Thanks. > > > Best, > > Robin > > > 2012/6/5 Kim, Hyojoon <jo...@gatech.edu> > > Hi all, > > > > > What is the most common way to do layer-2 network topology discovery in > OVS? Some searching gives me a hint that people install lldpd, and query > that table once it’s populated. Is this the most common way? > > > > > I figured out there is no SNMP support in OVS, but there is sFlow. Is > sFlow in OVS capable of doing topology discovery? It gives me a feeling > that it is more about traffic monitoring. > > > > > Thanks, > > > Joon > > > > _______________________________________________ > > discuss mailing list > > discuss@openvswitch.org > > http://openvswitch.org/mailman/listinfo/discuss > > > > _______________________________________________ > > discuss mailing list > > discuss@openvswitch.org > > http://openvswitch.org/mailman/listinfo/discuss > > > > > _______________________________________________ > discuss mailing list > discuss@openvswitch.org > http://openvswitch.org/mailman/listinfo/discuss > > >
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