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Routing Information Protocol is a one of many routing protocols used today. It is situated in the Application Layer. It use distance vectors to identify the best path to any given destination address. Routing Information Protocol is normally used for local area networks and wireless area networks. This is a protocol that is stable. This stability is ensured by quickly and efficiently adapting the routes the data packets that to get to their destination.
RIP work is a database. This routing database has info on all the best and fastest routes from pc to pc. This database is uses an algorithm to update frequently. All routers have access to this routing database and uses it to choose the fastest route to destination.
The Database is stored on the router. It contains data on every computer on the network. The Database contains:
Address op the computer
Message service to send IP addresses
The number of hops from router to router (Info also included in message)
Route Change Flag
Updates what happens to data on other Databases
The Database makes use of an Algorithm. It updates at regular intervals with other routers on the network. This is very important
A mathematical description of this algorithm is shown below.
Let D(i,j) be the metric for the best route from router i to router j.
Let d(i,j) represent the distance from router i to router j, set to infinite if i and j are the same or if i and j are not immediate neighbors.
The best distance is then
D ( i, i ) = 0, for all i
D ( i, j ) = min ( d ( i, k ) + D ( k, j ) ), for i <> j, over all k
The RIP algorithm converged to the best estimates of distance to each destination address and was thought up by D. P. Bertsekas and R. G. Gallaher.
The RIP routing protocol uses UDP. RIP was limited by the maximum number of hops of 15.
RIP version 1
Do not carry subnet info.
RIP version 2
Does carry subnet info.
Interior Gateway Routing Protocol
IGRP is also a distance vector protocol but is used for interior routing. Instead of using a metric system is uses an autonomous system to update its neighboring router. The developers Cisco developed this protocol to overcome the RIP protocol maximum number of hops. IGRP can now do 255 hops. The default setting is 100 hops. IGRP uses bandwidth and line delay by default for determining the best.
Hold-downs are used to regulate router to router updates. This is used to cancel out a route that is bad. When a router fails all the other neighboring router picks up that there is no activity. This is normally picked up every 90 seconds. The neighboring routers send out a message to the other routers and a sort of message wave is formed to update all the routers. This process takes a while. Hold-downs tell routers to not change any data of routes for a period of time; this time is normally just greater than the period of time necessary to update the entire network with a routing change.
Split Horizons are used to send data back of the best possible route. IGRP uses it to provide extra algorithm stability. It should prevent routing loops between adjacent routers. This is not always the case but poison-reverse updates are necessary to defeat larger routing loops. Poison-reverse updates then are sent to remove the route and place it in hold-down.Â
Update Timer: How frequently a update messages should be sent out to other routers.Â Variable: 90 seconds
Invalid TimerÂ - How long a router should wait, to send a invalid message. (If router is unavailable) Variable: x3 the update period.
Hold down Timer- How long the hold-down period is Variable: x3 the update period + 10 sec.
Flush TimerÂ - How much time should pass before a route should be removed or flushed from the routing table. Variable: x7 the update period.
Enhanced Interior Gateway Routing Protocol
EIGRP is an advanced version of IGRP. Provides superior convergence, operating efficiency and combines link-state protocol with distance-vector protocols.
Since the path through Router Three is three hops, and the path through Router One is two hops, Router Two chooses the path through One and discards the information it learned through Three. If the path between Router One and Network A goes down, Router Two loses all connectivity with this destination until it times out the route of its routing table (three update periods, or 90 seconds), and Router Three re-advertises the route (which occurs every 30 seconds in RIP).
EIGRP, instead of counting on full periodic updates to re-converge, builds a topology table from each of its neighbor's advertisements (rather than discarding the data), and converges by either looking for a likely loop-free route in the topology table, or, if it knows of no other route, by querying its neighbors. Router Two saves the information it received from both Routers One and Three
It chooses the path through One as its best path (the successor) and the path through Three as a loop-free path (a feasible successor). When the path through Router One becomes unavailable, Router Two examines its topology table and, finding a feasible successor, begins using the path through Three immediately.
Open Shortest Path First
OSPF is a link state or SPF protocol used in the TCP/IP Internet environment.
Supports classless routing
Better load balancing
Logical definition of areas
Authentication and external routes tagging
The main difference between OSPF and RIP is that RIP only keeps track of the closest router for each destination address, while OSPF keeps track of a complete topological database of all connections in the local network. The OSPF algorithm works as described below.
Startup. When a router is turned on it sends Hello packets to all of its neighbors, receives their Hello packets in return, and establishes routing connections by synchronizing databases with adjacent routers that agree to synchronize.
Update. At regular intervals each router sends an update message called its "link state" describing its routing database to all the other routers, so that all routers have the same description of the topology of the local network.
Shortest path tree. Each router then calculates a mathematical data structure called a "shortest path tree" that describes the shortest path to each destination address and therefore indicates the closest router to send to for each communication; in other words -- "open shortest path first".