How to: use IS-IS overload bit

August 30th, 2010 Wael Osama Posted in CISCO HOW-TO, ISIS, Network Design No Comments »

Overload bit is special bit in the IS-IS LSP used to inform the network that the advertising router is not yet ready to forward transit traffic.  The overload bit was first intended for signaling overload or resource shortage on specific router for the rest of the network. You can use the command set-overload-bit intentionally on [...]

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

May 22nd, 2010 mmahmoud Posted in Bury the hatchet, IGP, ISIS, Network Design, OSPF, Routing 2 Comments »

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.

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

May 16th, 2010 mmahmoud Posted in Bury the hatchet, IGP, ISIS, Network Design, OSPF, Routing 3 Comments »

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 [...]

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

April 26th, 2010 mmahmoud Posted in Bury the hatchet, IGP, ISIS, Network Design, OSPF, Routing No Comments »

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.

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IS-IS DIS in Practice

April 12th, 2010 Mounir Mohamed Posted in ISIS 1 Comment »

In the previous post IS-IS Neighbor Discovery we have discussed how IS-IS automatically discovers neighbors, in this post we will discuss the DIS role in broadcast networks. After the adjacency state reached the UP state the DIS election process take place, the router with the highest priority value (0-127 specified in the Priority field of [...]

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IS-IS Neighbor Discovery

April 12th, 2010 Mounir Mohamed Posted in ISIS 3 Comments »

Like other routing and signaling protocols IS-IS has built-in automatic neighbor discovery mechanism which is known by IIHs (IS-IS Hello PDUs), because IS-IS is not IP based protocol the IIH PDUs and all other IS-IS PDUs are directly encapsulated on the data-link layer. IS-IS has two hierarchical levels (L1 and L2) and two network types [...]

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