background preloader

Open Shortest Path First (OSPF)

Facebook Twitter

Open Shortest Path First (OSPF) CCNA R&S Exam Course. Chapter 12. Link-State Protocols: Open Shortest Path First (OSPF) Chapter 12.

Chapter 12. Link-State Protocols: Open Shortest Path First (OSPF)

Link-State Protocols: Open Shortest Path First (OSPF) Since its conception in 1987, OSPF has continued to evolve with the modern internetwork. Today, OSPF is clearly the dominant Open Systems interior routing protocol. Because of the constant RFC enhancements to OSPF, it has proven itself to be a scalable protocol with networks in the tens of thousands of nodes. OSPF officially was documented in 1989 by the Internet Engineering Task Force (IETF) to address many of the limitations of distance vector protocols, such as RIP and IGRP. As previously mentioned, OSPF provides many significant enhancements over current distance vector protocols: Fast convergence— OSPF uses a reliable flooding mechanism to update neighboring routers of changes in network topology.

In spite of these advantages, OSPF has been criticized as being overly complicated to configure and requiring high processor utilization. Fun with OSPF LSA Type 5, External Type 1. So maybe you're running around, getting last minute presents, trying to work a ton today so you can rest easy over the long weekend... and you need a break.

Fun with OSPF LSA Type 5, External Type 1

Coffee at the local Panera, whilst listening to even more Christmas carols? Stopping by holiday party leftovers in the conference room? Or how about refreshing your memory on how OSPF deals with External type 1 LSAs? For those of you opting for the latter, if you didn't do so already, check out the previous post on Type 5 external type 2 LSAs. To create an "E1" (OSPF type 5, external metric type 1) LSA, the router injecting the LSA into OSPF - the ASBR - must override the default of E2, specifically choosing to inject the route as an E1.

Of these points, the first 5 are true about both E1 and E2 routes. The Type 4 LSA exists so that the cost for E1 routes can be calculated. 1. In the example figure, R1 still floods the Type 5 LSA with cost 10. I see a Type 5 LSA, metric type E1 - what RID is listed? Fun with OSPF LSA Type 5, External Type 1. Fun with OSPF LSA Type 5, External Type 1. Open Shortest Path First. OSPF is perhaps the most widely used interior gateway protocol (IGP) in large enterprise networks.

Open Shortest Path First

Intermediate System to Intermediate System (IS-IS), another link-state dynamic routing protocol, is more common in large service provider networks. The most widely used exterior gateway protocol is the Border Gateway Protocol (BGP), the principal routing protocol between autonomous systems on the Internet. Overview[edit] The OSPF routing policies for constructing a route table are governed by link cost factors (external metrics) associated with each routing interface. Cost factors may be the distance of a router (round-trip time), data throughput of a link, or link availability and reliability, expressed as simple unitless numbers. An OSPF network may be structured, or subdivided, into routing areas to simplify administration and optimize traffic and resource utilization. By convention, area 0 (zero), or, represents the core or backbone area of an OSPF network. Hello Area types[edit] OSPF Feature Guide for Routing Devices.

OSPF is an interior gateway protocol (IGP) that routes packets within a single autonomous system (AS).

OSPF Feature Guide for Routing Devices

OSPF uses link-state information to make routing decisions, making route calculations using the shortest-path-first (SPF) algorithm (also referred to as the Dijkstra algorithm). Each router running OSPF floods link-state advertisements throughout the AS or area that contain information about that router’s attached interfaces and routing metrics. Each router uses the information in these link-state advertisements to calculate the least cost path to each network and create a routing table for the protocol. Junos OS supports OSPF version 2 (OSPFv2) and OSPF version 3 (OSPFv3), including virtual links, stub areas, and for OSPFv2, authentication. Junos OS does not support type-of-service (ToS) routing. OSPF routes IP packets based solely on the destination IP address contained in the IP packet header. An OSPF AS can consist of a single area, or it can be subdivided into multiple areas. Introduction to OSPF Part 1.