Category Archives: Networking

Cisco IOS Task Automation

If you love your server or desktop operating system’s CLI as much as myself you have probably banged out a few scripts to automate tasks at least a time or two… Did you know you can also script and automate tasks on Cisco IOS networking devices? The options are wrapped around the built in embedded event manager. The embedded event manager, or EEM for short, can track a number of sources including the syslog, SNMP, timers, counters and more. These are called event detectors. When an event is detected a policy can be trigged and some action taken. These actions … Continue reading

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Collecting CLI Data from Cisco Devices Via HTTP

I always try to approach technical challenges with the thought that “just because something can’t be done doesn’t mean it can’t be done”.   Sure enough I had a problem like this cross my desk again the other day.   I wanted a simple way to get the number of active calls on a handful of MGCP PRI gateway routers.  Unfortunately I couldn’t find a single SNMP data point for this information.  I knew IOS routers had an HTTP interface so I started checking around to see how easy it would be to script against. Sure enough, it really wasn’t all that … Continue reading

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Understanding Prefix Lists

When filtering and manipulating routing protocols and routing updates there are a number of options on the Cisco platforms we as engineers can take advantage of.  In a previous post I briefly discussed the use of standard ACL’s to filter updates.  ACLs filter every packet, or in this case advertised network, that falls within the range is specifies.  This is useful for all or nothing or specific inclusions but does not allow us to us easily filter or permit based on the actual prefix length, ie subnet mask length.  Enter prefix lists. To begin the discussion lets establish a topology … Continue reading

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EIGRP Route Filtering with ACLs

There are a number of reasons to implement route filtering. The filters can be used to control what routes are sent as well as what routes are learned from a neighbor. With ACLs the configuration is very flexible so just about anything is possible! Continue reading

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