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Author Archives: Adam
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
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
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
IPv6 Access List Basics
Chances are that if you have worked with IPv4 on the IOS platform for any length of time you are familiar with the access list formats, both standard and extended. Assuming you know at least the basics of the addressing structure you should have no issue establishing similar ACLs for IPv6. Creating IPv6 ACLs The first considerations are that IPv6 ACLs have to be the “extended” format meaning the both the source and destinations have to be defined. The ACLs also have to be named with a string as numbered ACLs are not acceptable. The ACL name can contain numbers … Continue reading
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