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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VRF Lite

February 15th, 2009 Wael Osama Posted in CISCO HOW-TO, MPLS 7 Comments »

// < ![CDATA[ google_ad_client = "ca-pub-5272078080280462"; /* upper-left-sq */ google_ad_slot = "5606795637"; google_ad_width = 200; google_ad_height = 200; // ]]> The word VRF stands for Virtual Routing and Forwarding, this feature is used to create multiple instances of the routing table on the same routing device. VRFs are usally used in conjunction with MPLS VPN [...]

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BGP Route Reflector Basics

February 12th, 2009 Wael Osama Posted in BGP, CISCO HOW-TO 18 Comments »

// < ![CDATA[ google_ad_client = "ca-pub-5272078080280462"; /* upper-left-sq */ google_ad_slot = "5606795637"; google_ad_width = 200; google_ad_height = 200; // ]]> Everyone who ever studied BGP knows that BGP has strong rules to prevent routing and updates loops. In this post I will focus on iBGP loop prevention and specifically route reflectors as a result. The rule states: [...]

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distribute-list gateway with OSPF

October 18th, 2008 Wael Osama Posted in CISCO HOW-TO, OSPF 2 Comments »

The following example is showing how to use distribute-list with the gateway option for inbound route filtering  in OSPF. The diagram below shows R1 directly connected to R2 with OSPF configured between them. Initial Configuration: !– R1 OSPF configuration router ospf 1 router-id 1.1.1.1 log-adjacency-changes network 172.16.12.1 0.0.0.0 area 0 network 172.16.101.1 0.0.0.0 area 0 [...]

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BGP Default-Originate insights

October 16th, 2008 Wael Osama Posted in BGP, CISCO HOW-TO No Comments »

BGP has multiple ways of advertising a default route to its neighbors;  the neighbor default-originate command is one of these methods and used to advertise a default route to a specific neighbor. Below are some characteristics of the default route advertised by this way. Originator router: Default route does not need to be existing in [...]

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How-to: Avoid DNS lookup when mistyping a command

August 6th, 2008 Wael Osama Posted in CISCO HOW-TO, IP Services 3 Comments »

If domain lookup is enabled (default) the router treats each mistyped command as a hostname and tries to resolve its IP address by querying the DNS server. This behavior is undesirable in most cases because it wastes network administrators time waiting for routers trying to resolve mistyped commands. R2#xyz Translating “xyz”…domain server (255.255.255.255) Translating “xyz”…domain [...]

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