BGP Attributes: Local Preference Attribute

December 18th, 2010 Wael Osama Posted in BGP 2 Comments »

The local preference attribute is a well-know discretionary attribute. This means local preference must be recognized by all BGP implementations, but will not exist in all BGP update messages; specifically it will not exist in E-BGP update messages. BGP local preference attribute is one of the most used attributes in BGP real world to influence [...]

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BGP Attributes: Atomic Aggregate Atribute

December 14th, 2010 Wael Osama Posted in BGP 3 Comments »

Atomic aggregate is a Well-known Discretionary attribute; it must be recognized by all BGP implementations and does not have to exist in all BGP updates. The purpose of the attribute is to alert BGP speakers along the path that some information have been lost due to the route aggregation process and that the aggregate path [...]

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BGP Attribute Types and Flags

December 8th, 2010 Wael Osama Posted in BGP 5 Comments »

BGP attributes is an interesting subject of study.  BGP is a very flexible and extensible protocol and I like that, let’s see how flexible is that protocol when it comes to attributes handling. We all know that BGP has four types of attributes as listed: Well-known mandatory. Well-known discretionary. Optional transitive. Optional non-transitive. I am [...]

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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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