also known as “routing by rumor”. The understanding that a router has of the network is based upon the perspective of the adjacent router of the network topology. Examples of distance-vector protocols include the following: Link-state routing protocols were designed to overcome limitations of distance vector routing protocols. Link-state routing protocols respond quickly to network changes sending trigger updates only when a network change has occurred. Link-state routing protocols send periodic updates, known as link-state refreshes, at longer time intervals, such as every 30 minutes. When a route or link changes, the device that detected the change creates a link-state advertisement (LSA) concerning that link. The LSA is then transmitted to all neighboring devices. Each routing device takes a copy of the LSA, updates its link-state database, and forwards the LSA to all neighboring devices. This flooding of LSAs is required to ensure that all routing devices create databases that accurately reflect the network topology before updating their routing tables. Link-state algorithms typically use their databases to create routing table entries that prefer the shortest path. Examples of link-state protocols include Open Shortest Path First (OSPF) and Intermediate System-to-Intermediate System (IS-IS). Interactive Media Activity Checkbox: Link-State and Distance Vector Routing Protocols After completing this activity, the student will be able to identify the difference between link-state and distance vector routing protocols. Web Links Distance Vector versus Link State http://www.inetdaemon.com/tutorials/ internet/routing/ dv_vs_ls.html
Content 10.2 IP Routing Protocols 10.2.9 Routing protocols RIP is a distance vector routing protocol that uses hop count as its metric to determine the direction and distance to any link in the internetwork. If there are multiple paths to a destination, RIP selects the path with the least number of hops. However, because hop count is the only routing metric used by RIP, it does not always select the fastest path to a destination. Also, RIP cannot route a packet beyond 15 hops. RIP Version 1 (RIPv1) requires that all devices in the network use the same subnet mask, because it does not include subnet mask information in routing updates. This is also known as classful routing. RIP Version 2 (RIPv2) provides prefix routing, and does send subnet mask information in routing updates. This is also known as classless routing. With classless routing protocols, different subnets within the same network can have different subnet masks. The use of different subnet masks within the same network is referred to as variable-length subnet masking (VLSM). IGRP is a distance-vector routing protocol developed by Cisco. IGRP was developed specifically to address problems associated with routing in large networks that were beyond the range of protocols such as RIP. IGRP can select the fastest available path based on delay, bandwidth, load, and reliability. IGRP also has a much higher maximum hop count limit than RIP. IGRP uses only classful routing. OSPF is a link-state routing protocol developed by the Internet Engineering Task Force (IETF) in 1988. OSPF was written to address the needs of large, scalable internetworks that RIP could not. Intermediate System-to-Intermediate System (IS-IS) is a link-state routing protocol used for routed protocols other than IP. Integrated IS-IS is an expanded implementation of IS-IS that supports multiple routed protocols including IP. Like IGRP, EIGRP is a proprietary Cisco protocol. EIGRP is an advanced version of IGRP. Specifically, EIGRP provides superior operating efficiency such as fast convergence and low overhead bandwidth. EIGRP is an advanced distance-vector protocol that also uses some link-state protocol functions. Therefore, EIGRP is sometimes categorized as a hybrid routing protocol. Border Gateway Protocol (BGP) is an example of an External Gateway Protocol (EGP). BGP exchanges routing information between autonomous systems while guaranteeing loop-free path selection. BGP is the principal route advertising protocol used by major companies and ISPs on the Internet. BGP4 is the first version of BGP that supports classless interdomain routing (CIDR) and route aggregation. Unlike common Internal Gateway Protocols (IGPs), such as RIP, OSPF, and EIGRP, BGP does not use metrics like hop count, bandwidth, or delay. Instead, BGP makes routing decisions based on network policies, or rules using various BGP path attributes. Lab Activity Lab Exercise: Small Router Purchase This lab is to introduce the variety and prices of network components in the market. This lab will look specifically at small routers used by telecommuters when working from home. Web Links Routing Basics http://www.cisco.com/univercd/cc/td/ doc/cisintwk/ito_doc/routing.htm
Content 10.3 The Mechanics of Subnetting 10.3.1 Classes of network IP addresses Classes of IP addresses offer a range from 256 to 16.8 million hosts, as discussed previously in this module. To efficiently manage a limited supply of IP addresses, all classes can be subdivided into smaller subnetworks. Figure provides an overview of the division between networks and hosts. Web Links IP Addressing Fundamentals http://support.wrq.com/tutorials/ tutorial.html
Content 10.3 The Mechanics of Subnetting 10.3.2 Introduction to and reason for subnetting To create the subnetwork structure, host bits must be reassigned as network bits. This is often referred to as ‘borrowing’ bits. However, a more accurate term would be ‘lending’ bits. The starting point for this process is always the leftmost host bit, the one closest to the last network octet. Subnet addresses include the Class A, Class B, and Class C network portion, plus a subnet field and a host field. The subnet field and the host field are created from the original host portion of the major IP address. This is done by assigning bits from the host portion to the original network portion of the address. The ability to divide the original host portion of the address into the new subnet and host fields provides addressing flexibility for the network administrator. In addition to the need for manageability, subnetting enables the network administrator to provide broadcast containment and low-level security on the LAN. Subnetting provides some security since access to other subnets is only available through the services of a router. Further, access security may be provided through the use of access lists. These lists can permit or deny access to a subnet, based on a variety of criteria, thereby providing more security. Access lists will be studied later in the curriculum. Some owners of Class A and B networks have also discovered that subnetting creates a revenue source for the organization through the leasing or sale of previously unused IP addresses. A LAN is seen as a single network with no knowledge of the internal network structure. This view of the network keeps the routing tables small and efficient. Given a local node address of 192.168.10.14, the world outside the LAN sees only the advertised major network number of 192.168.10.0. The reason for this is that the local address of 192.168.10.14 is only valid within the LAN 192.168.10.0 and cannot function anywhere else. Web Links IP Address Subnetting Tutorial http://www.ralphb.net/IPSubnet/
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