On Sun, Nov 14, 2010 at 08:59:33AM +0000, Paolo Lucente wrote:
On Sat, Nov 13, 2010 at 09:17:55PM -0600, Richard A Steenbergen wrote:
Oh and the sFlow on EX is actually pretty cripled when used for routing. It's missing support for a bunch of important extended message tpes, and doesn't fully populate all of the fields of the message types it does send. For example you won't get any data on ASNs, nexthops, dest ifindexes, or even netmasks of the src/dst route the flow matched, making it pretty darn useless for a lot of tasks. It's functional if you're just analyzing L2 networks at any rate.
Agree people spend some money and hence tend to expect something in return. But it's also true those good souls developing free collectors (to stay in topic with the OP) sometimes come to the rescue: ASNs, BGP next-hop, routes, netmasks can be all looked up at the collector at pretty no major effort. Variety of methods available depending on the collector, in place or a posteriori, file or BGP lookup - it's matter of selecting what fits better the specific job.
Yes you can do an offline routing lookup to try and reconstruct some missing data (or do some even more interesting analysis, as described in http://www.nanog.org/meetings/nanog35/presentations/steenbergen.pdf), but it isn't always a practical solution to missing netmask, nexthop, and dest ifindex data. Remember that every RIB in your network can and will have a unique best path selection (thanks to the EBGP > IBGP rule if nothing else), and if you have a network of any size at all you'll probably have to deal with multiple exits to the same network. Even if you were only concerned with analyzing external traffic, you'd still need to collect a RIB per edge router using an IBGP feed. In my network this would put you well over 10 million paths, and consume several gigs of ram, not to mention the load of doing the routing lookups themselves. If you wanted to do traffic analysis inside your network you'd need a feed from every router, and maybe even active participation in your IGP. It CAN be done, but it's not pretty, and I don't think any existing free software has been tested under these kinds of conditions. So when a vendor says "we support sFlow", make sure they actually support the message types and fields you need. :) -- Richard A Steenbergen <ras@e-gerbil.net> http://www.e-gerbil.net/ras GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)