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Bury the hatchet

The endless story of OSPF vs IS-IS – Part 4 “The Inside Out”

In this post we’ll be covering a couple of topics from the Inside Out of the link-state protocols that have always been ambiguous and full of details, we’ll try to make them as crystal clear as we can. MTU: Both link-state routing protocols consider MTU in order to prevent any related problems, mainly loss of routing information due to large routing messages being dropped (consider an OSPF LSU or an IS-IS LSP that is over sized and thus dropped), however each protocol tests the MTU in a different way as we’ll see in the upcoming section. OSPF requires routers to …

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The endless story of OSPF vs IS-IS – Part 3 “Packets and Database”

In this post we are going to cover the protocol packets and database structure for both routing protocols. To start let’s first highlight a couple of facts. OSPF runs on top of IP, that is it uses IP packets to exchange its messages (and thus it is vulnerable to spoofing and DoS attacks, and accordingly the use of authentication is strongly recommended), while on the other hand IS-IS runs directly over layer 2, it creates its own packet (or PDU (Protocol Data Unit) to be more specific) and then encapsulates it directly inside the layer 2 frame, this leverages IS-IS …

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The endless story of OSPF vs IS-IS – Part 2 “The history”

In our previous post we started consolidating the endless story of OSPF vs IS-IS, in this post we will cover the historical part of the story, it might not be interesting for some people, but I do believe that the history is what makes the future, so please bare with me through this post. The IS-IS protocol was developed in 1987 by Digital Equipment Corporation (DEC) as part of DECnet Phase V. and was standardized later in 1992 by the International Standards Organization (ISO) in ISO/IEC 10589:1992, the second and current edition ISO/IEC 10589:2002 cancels and replaces the first edition. …

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The endless story of OSPF vs IS-IS

Whenever you have a little IGP chit chat you’ll hit this endless story. I’ve tried to reach a final solid conclusion my self but IMHO its all about personal preference and taste. It is something like a Ferrari vs Lamborghini story, they offer comparable performance, but totally different feeling. It is all about a good design, that contains a balanced mixture of scalability, convergence, flexibility, extensibility, resources consumption, configuration, troubleshooting, etc. In this series of posts I’ll try to contrast their likes and differences (not the Ferrari vs Lamborghini of course!), however I am not going to try to influence …

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MTU and ping size confusion

I am very glade to return back after pausing posting for a while. Actually we were very busy the last few months evaluating, designing and preparing for our company’s backbone migration, a little C Vs J with all its fun 😉 Anyway, while going through the low level design we faced a little confusion when evaluating the MTU issues with MPLS running over. In the past we used to conduct the tests with Cisco’s IOS extended ping, but now we have IOS XR and JUNOS in addition, and we were hit by the fact of the difference in behavior. Digesting …

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VRF Selection Based on Source IP Addresses

In this post we are going to cover a nice tool, actually I’ve never used it in production, but I was fully testing it during my CCIE SP lab preparations and wish to share it with you. It’s nice to have such a tool in your tool box when dealing with complex designs. The VRF Selection feature allows a certain interface on a PE router to route packets received from the CE router to different VRFs based on the source IP address of the packet, imagine it as a form of policy-based routing, where you control the traffic forwarding based …

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