16-04-2013, 04:26 PM
Dynamic Routing Protocols IRIP
Dynamic Routing.ppt (Size: 985 KB / Downloads: 24)
Autonomous Systems
An autonomous system is a region of the Internet that is administered by a single entity.
Examples of autonomous regions are:
UVA’s campus network
MCI’s backbone network
Regional Internet Service Provider
Routing is done differently within an autonomous system (intradomain routing) and between autonomous system (interdomain routing).
Components of a Routing Algorithm
A procedure for sending and receiving reachability information about network to other routers
A procedure for calculating optimal routes
Routes are calculated using a shortest path algorithm:
Goal: Given a network were each link is assigned a cost. Find the path with the least cost between two networks with minimum cost.
A procedures for reacting to and advertising topology changes
A network as a graph
In the following, networks are represented as a network graph:
nodes are connected by networks
network can be a link or a LAN
network interface has cost
networks are destinations
Net(v,w) is an IP address of a network
For ease of notation, we often replace the clouds between nodes by simple links.
Characteristics of Distance Vector Routing
Periodic Updates: Updates to the routing tables are sent at the end of a certain time period. A typical value is 90 seconds.
Triggered Updates: If a metric changes on a link, a router immediately sends out an update without waiting for the end of the update period.
Full Routing Table Update: Most distance vector routing protocol send their neighbors the entire routing table (not only entries which change).
Route invalidation timers: Routing table entries are invalid if they are not refreshed. A typical value is to invalidate an entry if no update is received after 3-6 update periods.
RIP - Routing Information Protocol
A simple intradomain protocol
Straightforward implementation of Distance Vector Routing
Each router advertises its distance vector every 30 seconds (or whenever its routing table changes) to all of its neighbors
RIP always uses 1 as link metric
Maximum hop count is 15, with “16” equal to “”
Routes are timeout (set to 16) after 3 minutes if they are not updated