COMPUTER SCIENCE: August 2014

Tuesday, 26 August 2014

Routing Information Protocol (RIP)

Routing Information Protocol (RIP) is a true distance-vector routing protocol. It sends the complete routing table out to all active interfaces every 30 seconds. RIP only uses hop count to determine the best way to a remote network, but it has a maximum allowable hop count of 15 by default, meaning that 16 is deemed unreachable. RIP works well in small networks, but it’s inefficient on large networks with slow WAN links or on networks with a large number of routers installed.

RIP version 1 uses only classfull routing, which means that all devices in the network must use the same subnet mask. This is because RIP version 1 doesn’t send updates with subnet mask information in tow. RIP version 2 provides something called prefix routing, and does send subnet mask information with the route updates. This is called classless routing.

Summary:-

v Works on application layer

v Open standard protocols

v Dynamic routing protocols

v Supports hop -count matric

v Support maximum 15 hop-count

v Support six equal cost path

v Used distance vector algorithms

v It only check the neighbour

v Its only exchange the updates or routing table with neighbour

v Two type of version

1. RIP V-1 2.RIP V-2

RIP Timers

RIP uses three different kinds of timers are following:-

Update timer:-

Sets the interval (typically 30 seconds) between periodic routing updates,in which the router sends a complete copy of its routing table out to all neighbors.

Invalid timer:-

Determines the length of time that must elapse (180 seconds) before a router determines that a route has become invalid. It will come to this conclusion if it hasn’t heard any updates about a particular route for that period. When that happens, the router will send out updates to all its neighbors letting them know that the route is invalid.

Holddown timer:-

This sets the amount of time during which routing information is suppressed. Routes will enter into the holddown state when an update packet is received that indicated the route is unreachable. This continues until either an update packet is received with a better metric or until the holddown timer expires. The default is 180 seconds.

Flush timer:-

Sets the time between a route becoming invalid and its removal from the routing table (240 seconds). Before it’s removed from the table, the router notifies its neighbors

of that route’s impending demise. The value of the route invalid timer must be less than that of the route flush timer. This gives the router enough time to tell its neighbors about the invalid route before the local routing table is updated.

Friday, 22 August 2014

Autonomous System (Internet)

An autonomous system (AS) is the unit of router policy, either a single network or a group of networks that is controlled by a common network administrator (or group of administrators) on behalf of a single administrative entity (such as a university, a business enterprise, or a business division). An autonomous system is also sometimes referred to as a routing domains . An autonomous system is assigned a globally unique number, sometimes called an Autonomous System Number (ASN).

Networks within an autonomous system communicate routing information to each other using an Interior Gateway Protocol (IGP ). An autonomous system shares routing information with other autonomous systems using the Border Gateway Protocol (BGP ). Previously, the Exterior Gateway Protocol (EGP) was used. In the future, the BGP is expected to be replaced with the OSI Inter-Domain Routing Protocol (IDRP)

Range from 1-65535.

AD VALUE (Administrative distance){0-255}

Administrative distance (AD) is an arbitrary numerical value assigned to a routing protocol, a static route or a directly-connected route based on its perceived quality of routing. The administrative distance (AD) value is often used by Cisco routers to determine the "best" route that should be used when multiple paths to the same destination exist. A routing protocol with a lower administrative distance is considered "better" and is given priority over routing protocols with higher administrative distances. The "better" route is selected by the router and is inserted into the router's routing table to be used to route traffic. For example, routes issued by EIGRP are considered more reliable than routes issued by RIP. This is because EIGRP has an administrative distance of 90 while RIP has an administrative distance of 120. The administrative distance (AD) value may be set manually by a network administrator. If a network administrator fails to properly set the administrative distance or configures multiple routing protocols with the same administrative distance, the router will use the default administrative distance.