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CISCO HOW-TO

How to: use IS-IS overload bit

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 …

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VRF Lite

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 to separate the traffic of multiple MPLS VPN customers. VRF Lite feature is part of …

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BGP Route Reflector Basics

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: that any route received from an iBGP neighbor must not be advertised to any other …

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distribute-list gateway with OSPF

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 …

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BGP Default-Originate insights

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 …

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