The internals of libpcap a case

Transmission Control Protocol 3. Data Link Provider Interface.

The internals of libpcap a case

Some state that observability is a replacement for monitoring.

The internals of libpcap a case

Others that they are parallel mechanisms, or that one is a subset of another not to mention where tracing fits into such a hierarchy. Monitoring Weekly recently provided a helpful list of resources for an overview of this discussion, as well as some practical applications of observability.

One can go back even further to the Apollo 11 source code to see some of the earliest implementations of software observability, and also systems monitoring from mission control. If we ask Wikipedia what Observability is, we get an answer along the lines of how well internal states of a system can be inferred from knowledge of its external outputs.

To understand this distinction between monitoring and observability, consider what a doctor does with a stethoscope. One uses the external outputs of the stethoscope to determine the internal state of the patient.

The patient is monitored with instruments such as the stethoscope, and it is the observable traits of these instruments that allow this monitoring to occur. Our patient will be the Apache Cassandra wide column distributed data store.

Our stethoscope will be the wirelatency tool, which uses the libpcap library to grab a copy of packets off of the wire before they are processed by the operating system.

We are going to determine how well the internal states of Cassandra are by observing the external outputs the query latency data.

Pcap allows one to get a copy of packets off the ethernet interface at the link layer prior to their being handled by the kernel networking code.

Mar 12,  · Effective Communication Case Study Analysis Case Pepsi Syringe University of Phoenix Public Relations / MKT Charles Bocage, Dean of Education, Apagy Technology Group, MBA, MSIS, TQM January 22, Effective Communication Case Study Analysis Case. In the field of computer network administration, pcap (packet capture) consists of an application programming interface (API) for capturing network traffic. Unix-like systems implement pcap in the libpcap library; Windows uses a port of libpcap known as WinPcap. In this case an idea is to modify the internals of libpcap to support a minimal set of the pcap-ng features without changing the current API (e.g. files with only one section and packets from one interface).

The details of the implementation vary between operating systems, but packets essentially bypass the kernel network stack and are made available to user space.

These are often referred to as raw sockets. So now that we can grab packets off the wire in a computationally performant means, we can reassemble bidirectional TCP streams, decode application specific protocols, and collect telemetry.

Enter the wirelatency utility that was developed in Go. The gopacket library handles the reassembly of bidirectional data from the packets provided by pcap.


The circonus-gometrics library allows us to send that telemetry upstream to Circonus for analysis. Initially, I used an Ubuntu Fortunately, this was a documented issue.

I could have downgraded JDK or recompiled Cassandra from source and probably would have done so 10 years agobut I decided to take the easy route and lit up two new hosts running RHEL. It was a cake walk comparatively to get Cassandra up and running, so I used the excellent DataStax documentation to get a simple schema up and insert some data.

At this point, I was able to grab some network traffic. And because the packets are timestamped, we can calculate the query latency, which was about 7. We can see below how it tracks inbound and outbound TCP streams. It reassembles those streams, pulls out the Cassandra queries, and records the query latencies.

Conclusion We can get a look at the distribution of latencies observed by using a histogram to display that distribution. This histogram shows that a lot of requests are clustered between 2 and 4 milliseconds. We can also see a much smaller mode between 25 and 30 milliseconds.

This tells us that we likely have two different data access patterns going on for this example select query.

Observing Wirelatency and Monitoring Cassandra

If we had just looked at average query latency with a more blunt instrument, we would have probably concluded that most queries were taking around 10 milliseconds. But looking at the distribution here, we can see that very few queries actually took that long to execute.Find great deals on eBay for new laptop case.

The internals of libpcap a case

Shop with confidence. Aug 28,  · Yes libpcap/tcpdump is receiving a copy of the frames before they are being processed by SecureXL or the INSPECT driver on the inbound side.

The outbound side is a lot more complicated though depending on SecureXL and you may or may not see the packets leaving with tcpdump.

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WinPcap: NPF driver internals manual