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Getting Network Visibility a Bit at a Time

January 30, 2015

As a consultant I don’t usually get access to my customer’s network management system. Trust me, in many cases I am just fine with that.

When troubleshooting or installing new equipment, I want to gather statistics to ensure that the problem is resolved or the installed equipment is behaving properly and without some kind of network monitoring, a manual process is my only option. Lets face it; telnetting into equipment and looking at port counters is a bit painful at best.

In some smaller networks, my customers are under the impression that network monitoring systems cost tens of thousands of dollars, so go without having one.

When I introduce my customers to MRTG, an open source network monitoring system, eyes light up and people get excited about the possibilities of what value monitoring can provide. MRTG is great way to get started with your network monitoring and when you outgrow it, or need extra features, you now have the guidelines when you go shopping for a new monitoring system. I have clients still only using MRTG for the past 5 years because that’s all they need.

Just a quick review, SNMP monitoring is a great way to get started when monitoring your network devices, but as you evolve and learn about network monitoring in general, you should consider all the other points covering this topic. For example packet captures, monitoring conversation flows, security, etc.

I like MRTG because it is flexible, easy to setup and does not require a ton of RAM or CPU.  I’ve installed MRTG on laptops with a P4 processor and 2 G of RAM and it did the job.

I’ve used MRTG to monitor your typical values like packets, Bytes, bits, errors, etc. But I’ve also used it for some pretty cool stuff, like WiFi RSSI, UPS load and temperature. You can even graph the values in a file.

In this video I show you how to get up and running with a simple MRTG configuration in less than 5 minutes.

 

 

Tony Fortunato, CCNA, CFNI, CWI
Sr Network Performance Specialist
The Technology Firm
www.thetechfirm.com
Getting things to work better - bit by bit-

Linkedin Profile http://ca.linkedin.com/in/fortunat
Lovemytool Blog: http://www.lovemytool.com/blog/tony-fortunato/
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Heartbeats Packets Inside the Bypass TAP

If the inline security tool goes off-line, the TAP will bypass the tool and automatically keep the link flowing. The Bypass TAP does this by sending heartbeat packets to the inline security tool. As long as the inline security tool is on-line, the heartbeat packets will be returned to the TAP, and the link traffic will continue to flow through the inline security tool.

If the heartbeat packets are not returned to the TAP (indicating that the inline security tool has gone off-line), the TAP will automatically 'bypass' the inline security tool and keep the link traffic flowing. The TAP also removes the heartbeat packets before sending the network traffic back onto the critical link.

While the TAP is in bypass mode, it continues to send heartbeat packets out to the inline security tool so that once the tool is back on-line, it will begin returning the heartbeat packets back to the TAP indicating that the tool is ready to go back to work. The TAP will then direct the network traffic back through the inline security tool along with the heartbeat packets placing the tool back inline.

Some of you may have noticed a flaw in the logic behind this solution!  You say, “What if the TAP should fail because it is also in-line? Then the link will also fail!” The TAP would now be considered a point of failure. That is a good catch – but in our blog on Bypass vs. Failsafe, I explained that if a TAP were to fail or lose power, it must provide failsafe protection to the link it is attached to. So our network TAP will go into Failsafe mode keeping the link flowing.

Glossary

  1. Single point of failure: a risk to an IT network if one part of the system brings down a larger part of the entire system.

  2. Heartbeat packet: a soft detection technology that monitors the health of inline appliances. Read the heartbeat packet blog here.

  3. Critical link: the connection between two or more network devices or appliances that if the connection fails then the network is disrupted.

NETWORK MANAGEMENT | THE 101 SERIES