Chapter3 - Basic concepts of routing (Part2)

6. RIP (Routing Information Protocol)

• RIP is a distance vector routing protocol

• It has evolved over the years

• Hop count is the metric

• It helps prevent infinite routing loops

• If the number of hops is greater than 15, the packet is discarded

• Routing updates are broadcast every 30 seconds

• When a router receives a routing update containing a new or modified entry, the metric value increases by 1

7.Disadvantages of RIP

• RIP is outdated by the rapid expansion of networks,

• RIP V1 does not support VLSM

• Regularly broadcasting the full routing table uses too many BPs,

• Convergence is slower than that obtained by other routing algorithms

• Routers using RIP have blocking periods (garbage collection)

• RIP has no concept of cost

• RIP networks are flat (no concept of zones or boundaries)

• RIP V2 supports VLSM and multicast updates but has the same hop count and convergence limits

8. OSPF routing protocol

• OSPF favors the shortest path (Dijkstra algorithm)

• OSPF addresses all RIP issues

• No limit on the number of jumps

• The use of VLSM is very important

• Link-state algorithm

• Links= router interface

• Link state=description of the interface and its relationships with neighboring routers

• Description of a link = @IP, mask, type of network to which it is connected and the routers connected to this same network

• Description of all links -> Link status database

• Updated in case of modification and not periodically

• OSPF converges better than RIP

• OSPF allows for better load balancing

• OSFP allows the network to be divided into zones

8.1. The different update stages

• A router publishes the state of all its links during initialization or following a change in routing information,

• Each router that receives an update stores a copy in its link state database and floods it to all other routers.

• Zones are placed to limit flooding of Updates

• OSPF remains silent in case no changes occur.

• After receiving an update, Dijkstra's algorithm for calculating the shortest path is restarted,

• Dikstra places the router at the root of the tree and calculates the shortest path to each destination based on the cumulative cost

• Each router has its own view of the topology established from the same link state database,

• Once the router has created the tree, it creates the routing table

8.2. OSPF Cost

• OSPF Cost is a metric used to determine the shortest path to a destination in an OSPF network,

• Cost of an interface in OSPF is inversely proportional to the BP of the interface,

• A lower BP indicates a higher cost and vice versa, the formula used is:

8.3. Shortest path tree

8.4. zone notion

• Zones are introduced to place a limit on updates

• Dijkstra's algorithm and updates are made following changes in the area to which the router belongs

• All routers in an area have the exact link state BD,

• ABR: Area Border Routers, it has interfaces in multiple areas

• IR: internal router where all interfaces are in the same area

• ASBR: router that bridges OSPF and other routing protocols

                            Figure3.4 - Zone notion.