Saturday, September 13, 2014

No more duplicate frames with Gigamon Visibility Fabric


Gigamon presented their Visibility Fabric Architecture at Network Field Day 8.  You can watch the presentation at Tech Field Day.

CC BY-NC-ND 2.0 licensed photo by smif
Needs deduplication
One of the interesting facets of Gigamon's solution was it's ability to do real-time de-duplication of captured traffic as it traverses the Visibility Fabric (a hierarchy of monitoring data sources and advanced aggregation switches). I've spent some time around proactively-deployed network taps, but never seen this capability before, and I think it's pretty nifty.

The Problem
Let's say you've got taps and mirror ports deployed throughout your network. They're on the uplinks from data center access switches, virtually attached to vSwitches for collecting intra-host VM traffic, at the WAN and Internet edge, on the User distribution tier, etc...  All of these capture points feed various analysis tools via Gigamon's Visibility Fabric. It's likely that a given flow will be captured and fed into the monitoring infrastructure at more several points. Simplistic capture-port-to-tool-port forwarding rules will result in a given packet being delivered to each interested tool more than once, possibly several times.

This can be problematic because it confuses the analysis tool (ZOMG, look at all of those TCP retransmissions!), burns precious bandwidth on links within both the tap aggregation infrastructure and to the analysis tool, skews timestamps by introducing link congestion (not a problem for analyzers which leverage Gigamon's timestamp trailer) and wastes disk space when traffic is being written to disk.

Gigamon's Answer
When configured to suppress duplicates, Gigamon equipment will remember (for 50ms, by default) traffic it's sent to a given tool, and suppress delivery of duplicate copies collected in other parts of the infrastructure. The frames don't have to be exactly the same: A packet routed from one subnet to another will have a different Ethernet header. Apparently this is okay, and doesn't confuse the de-duplication filters. 802.1Q tags are probably okay too, though I think I heard that recognizing a VXLAN-encapsulated frame as a duplicate of a native Ethernet frame is beyond the capability of the de-dupe feature.

Even though Gigamon bufferes traffic for 50ms, there's no added latency introduced when suppressing duplicates. It's not like a jitter buffer. Rather, the first copy of a given packet is always delivered immediately. The buffer is used only to recognize duplicates which need to be suppressed.

Should you de-duplicate the traffic? Maybe. It depends on the tool and on the problem you and the tool are attacking.

Tools focused on application-layer analysis (IDS/IPS, DLP, user experience monitoring, etc...) probably don't generally need to see the same traffic as it appears at various points in the network and will benefit from de-duplication, while tools focused on infrastructure performance monitoring and post-incident analysis will want to see everything, and are likely deployed in such a way that they're already set up to differentiate between multiple copies of the same captured data.

I was a delegate and Gigamon was a presenter at NFD8. Gigamon paid some of the costs associated with putting on the event, and Gestalt Media covered the costs associated with getting me there, feeding me, etc... Also, I collected some vendor tchotchkes along the way. Neither Gigamon nor Gestalt IT bought my opinions, nor space on this blog. I writing about them because I found their presentation interesting, and for no other reason.

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