send infrequent or event triggered LSA packets reflecting topology changes. Web Links Routing Protocols - Link State http://www.firewall.cx/i ndex.php?c=link_state
Content 6.3 Routing Protocols Overview 6.3.1 Path determination A router determines the path of a packet from one data link to another, using two basic functions: Path determination occurs at the network layer. The path determination function enables a router to evaluate the paths to a destination and to establish the preferred handling of a packet. The router uses the routing table to determine the best path and proceeds to forward the packet using the switching function. - The switching function is the internal process used by a router to accept a packet on one interface and forward it to a second interface on the same router. A key responsibility of the switching function of the router is to encapsulate packets in the appropriate frame type for the next data link. Figure illustrates how routers use addressing for these routing and switching functions. The router uses the network portion of the address to make path selections to pass the packet to the next router along the path.
Content 6.3 Routing Protocols Overview 6.3.2 Routing configuration Enabling an IP routing protocol on a router involves the setting of both global and routing parameters. Global tasks include selecting a routing protocol, such as RIP, IGRP, EIGRP or OSPF. The major task in the routing configuration mode is to indicate IP network numbers. Dynamic routing uses broadcasts and multicasts to communicate with other routers. The routing metric helps routers find the best path to each network or subnet. The router command starts a routing process. The network command is required because it enables the routing process to determine which interfaces participate in the sending and receiving of routing updates. An example of a routing configuration is: GAD(config)#router rip
GAD(config-router)#network 172.16.0.0 The network numbers are based on the network class addresses, not subnet addresses or individual host addresses. Major network addresses are limited to Class A, B, and C network numbers. Lab Activity e-Lab Activity: Routing Configuration In this lab, the students will configure the routers to start a routing process, then add the networks that will be advertised.
Content 6.3 Routing Protocols Overview 6.3.3 Routing protocols At the Internet layer of the TCP/IP suite of protocols, a router can use an IP routing protocol to accomplish routing through the implementation of a specific routing algorithm. Examples of IP routing protocols include: Routing Information Protocol (RIP) was originally specified in RFC 1058. Its key characteristics include the following: Interior Gateway Routing Protocol (IGRP) is a proprietary protocol developed by Cisco. Some of the IGRP key design characteristics emphasize the following: Open Shortest Path First (OSPF) is a nonproprietary link-state routing protocol. The key characteristics of OSPF are as follows: EIGRP is a Cisco proprietary enhanced distance vector routing protocol. The key characteristics of EIGRP are as follows: Border Gateway Protocol (BGP) is an exterior routing protocol. The key characteristics of BGP are as follows: Interactive Media Activity Checkbox: Link-State and Distance Vector Routing Protocols After completing this activity, the student will be able to understand IP routing protocols. Web Links Introduction to IP Routing http://www.cisco.com/en/US/tech/tk365/tech_topology
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Content 6.3 Routing Protocols Overview 6.3.4 Autonomous systems and IGP versus EGP Interior routing protocols are designed for use in a network whose parts are under the control of a single organization. The design criteria for an interior routing protocol require it to find the best path through the network. In other words, the metric and how that metric is used is the most important element in an interior routing protocol. An exterior routing protocol is designed for use between two different networks that are under the control of two different organizations. These are typically used between ISPs or between a company and an ISP. For example, a company would run BGP, an exterior routing protocol, between one of its routers and a router inside an ISP. IP exterior gateway protocols require the following three sets of information before routing can begin: An exterior routing protocol must isolate autonomous systems. Remember, autonomous systems are managed by different administrations. Networks must have a protocol to communicate between these different systems. Autonomous systems have an identifying number, which is assigned to it by the American Registry of Internet Numbers (ARIN) or a provider. This autonomous system number is a 16-bit number. Routing protocols such as Cisco’s IGRP and EIGRP require that a unique, autonomous system number be assigned. Interactive Media Activity Checkbox: IGP versus EGP After completing this activity, the student will be able to understand IGP and EGP. Web Links IGP http://searchsecurity.techtarget.com/ sDefinition/0,,sid14_ gci214018,00.html
Content 6.3 Routing Protocols Overview 6.3.5 Distance vector Distance vector algorithms (also known as Bellman-Ford algorithms) call for each router to send all or