Author: ccie14023

IS-IS Levels and Adjacencies

In this post, we’ll be looking at IS-IS inter-area concepts, and hopefully clearing up some of the confusion ISIS areas create in the minds of engineers who are used to OSPF.  ISIS handles areas quite differently from OSPF, and if you think about ISIS areas in OSPF terms you are likely to be confused by some of this behavior.  The good news is that if you configure area numbers and enable ISIS, it should just work, but if you want to do anything more complex you will need a deeper understanding of how ISIS areas work.  I’ll assume you know the basics of ISIS, for example that it is not an IP native protocol, and just focus on the areas for now.  My intention here is not to go into all of the details of ISIS inter-area operation, but to help you sort out the basics in your mind so you can dive deeper in your studies. All output will be from Juniper routers, but should be self-explanatory enough for those of you using a different platform. When studying ISIS, you will typically come across an area diagram that looks like this: And as an OSPF engineer, you will typically think the following: Great!  The middle area (area 1) with the two L2 routers is like area 0.  The L1/L2 routers are the ABRs, which appear only on area...

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This is my first post on this blog which I created some time ago and have left dormant.  Give that there are about twice as many blogs as people, it would seem best to start out with a statement of my purpose and intent. Before that, a little background:  I currently work for Juniper Networks, although I don’t claim to speak for them.  I am responsible for network architecture within IT, which gives a unique perspective since I am both a customer and a vendor.  I’ve been working in this industry for over 15 years, although my history with computers goes back farther than that.  I hold dual CCIE certifications in Routing/Switching and Security, and an M.S. in Telecommunications Management.  Non-technical credentials:  I hold an FAA Private Pilot’s certificate, I have studied and taught Ancient Greek and Latin. My hope is to provide several types of articles here.   I specialize in communicating technical concepts in simple and direct language, so I will be breaking down difficult technical subjects for my readers, focusing particularly on subjects that frustrate me.  (Don’t get me started on MSTP).  I will also provide frank commentary on the industry, its trends, and on training and certification.  I will also augment this with stories from my years as a network engineer that hopefully will keep things entertaining.  Finally I hope my language and humanities experience...

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