Types of Routing Protocol


When describing types of routing protocols, it is first necessary to understand the concept of an autonomous system . Autonomous systems are best defined as collections of routers and networks that come under a common administrative control. An autonomous system could comprise an organization, such as a university campus. It is also sometimes called a routing domain and is identified by a globally unique 16-bit number ”assigned by the Internet Corporation for Assigned Names and Numbers (ICANN). The 16-bit number is often called an Autonomous System Number (ASN). There are two types of routing protocols: interior routing protocol and exterior routing protocol:

  • Interior routing protocol ” Interior routing protocols are used to route packets within an autonomous system, such as the departments of an organization. Two protocols, Routing Information Protocol (RIP) and Open Shortest Path First (OSPF), are the most common examples of IGPs, and have the following characteristics:

    • Routing Information Protocol (RIP) ” RIP is a distance-vector protocol that uses the number of hops taken to calculate the path to the destination. Using RIP, the entire routing table is passed to the closest neighbor, by default every 30 seconds. The process continues until each node contains the same network information, making it much slower to propagate changes to the route configuration because the entire routing table is transmitted each time a change occurs. RIP works well in smaller networks, but for larger networks, it can greatly increase the network traffic and affect the network's performance.

    • Open Shortest Path First (OSPF) ” OSPF is a link-state protocol that maintains a complex knowledge of the network topology. Information concerning the state of the network is exchanged between routers by a link-state advertisement (LSA). OSPF uses other information in addition to hop counts to determine the best route to a destination. A major difference from RIP is that when changes occur, it is not the entire routing table that is sent to other hosts , but only the changed part. As soon as a change is detected , the LSA is triggered, which means that routing tables can be updated to reflect the change more quickly than they would with RIP.

  • Exterior routing protocol ” Exterior routing protocols are used to route packets between autonomous systems, such as between organizations or universities. The two main exterior routing protocols are Exterior Gateway Protocol (EGP) and Border Gateway Protocol (BGP):

    • Exterior Gateway Protocol (EGP) ” EGP is used to exchange routing table information in a network of autonomous systems. Each router polls its neighbor at regular intervals (approximately every five minutes) and the neighbor's response consists of its entire routing table, which is similar to what happens with RIP. The routing table contains known routers and the addresses that the routers know about. Also included is a cost metric so that the optimal available route can be used to exchange data. The latest version of EGP is EGP-2, although EGP has been largely replaced by the Border Gateway Protocol (BGP) described next .

    • Border Gateway Protocol (BGP) ” BGP is a more recent exterior routing protocol than EGP and, like EGP, is used to exchange routing table information between autonomous systems. Like the interior routing protocol OSPF, BGP exchanges only the routing table changes, and not the entire routing table, as EGP does. BGP makes use of Classless InterDomain Addresses (CIDR), which are described later in this chapter and allow more addresses to be assigned within the network than are available with IPv4. The latest version of BGP is BGP-4, which allows the metrics assigned to a route to be configured by the network administrator.



Solaris 9 Network Administration Exam Cram 2 (Exam Cram CX-310-044)
Solaris 9 Network Administrator Exam Cram 2 (Exam CX-310-044)
ISBN: 0789728702
EAN: 2147483647
Year: 2003
Pages: 174
Authors: John Philcox

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