Dynamic routing protocols allow networks to keep routing tables up to date as the network changes over time. There are two main types of dynamic routing protocols: link-state protocols and vector-distance protocols. Link-state protocols have advantages like ensuring all routers converge on the same routing tables and generating less network traffic compared to vector-distance protocols. Common dynamic routing protocols include RIP, OSPF, IS-IS, and BGP.

1. Dynamic Routing Protocols A Brief Overview March 22, 2001 Professor Tom Mavroidis

2. Why Dynamic Routing For small networks static routing is fine As the network grows it becomes impossible to keep the routing tables consistent Dynamic Routing lets the network keep itself up to date

3. Routing Server or Routing Daemon On the internet gateway systems maintain up to date information about routes. Each router propagates its routing information to other routers in the network They also update their routing tables from information sent by other routers This process is known as the routing server or routing daemon

4. Dynamic Routing... Determines the information placed placed in the routing table If multiple routes are found the best route will be inserted into the routing table (choice is made according to a routing policy in the router)

5. Routing Protocols Two Classifications link-state protocols vector-distance protocols

6. ICMP Redirect Messages Simplest form of dynamic routing Host systems are initialized with minimal routing information If the router discovers better route to a particular host it send an ICMP redirect message to the router closer to the source who updates its routing table.

7. Vector-Distance Protocols Many vector-distance Protocols have been superseded by link-state Protocols (such as RIP and Hello) Vector-distance Protocols forward routes across the network form router to router Routes are sent as a table (Destination/Distance) If the destination does not exist in the routing table a new route is added

8. Vector-Distance continued If a route already exists it is updated both longer and shorter routes are updated since routes may have changed by a router coming off line or going on line Rip is the most popular vector-distance protocol was made available through the 4.2 BSD version of Unix Limits hops to 16 (therefore limits size of network)

9. Link-State Protocols OSPF - Open Shortest Path First Uses a graph searching algorithm Updates don’t contain routes only status of directly connected links When status changes the router rebuilds its graph and re-computes the routes

10. Advantages to Link-state Routing Each router re-computes routes independently Routers are guaranteed to converge - (agree between each other) Link Status messages pass across the network unchanged (easier to debug) Scaleable - message size doesn’t depend on the number of networks Generates less traffic on the network

11. Other Interior Gateway Protocols ICMP Router Discovery Protocol host selects the most appropriate default route work on an advertise/solicit mechanism host broadcasts a router solicitation message on startup Receiving routers send back an advertisement packet containing its IP address and a preference value host will select and update is routing table based on the best preference value

12. Other Interior Gateway Protocols Hello uses a time delay measurement to choose the best route IDRP - InterDomain Routing Protocol IS-IS - Intermediate system to Intermediate system

13. Exterior Gateways A collection of networks and routers under a single administrative control is known as an Autonomous System Central core network provides a method of connecting constituent networks Admin of the subsections is delegated to the core network Packets destined out of the interior network are forwarded to the exterior gateway

14. Exterior Gateways Greatly increase the scalability of the Internet backbone Alleviate bandwidth problems Keeps the size of of the routing tables to a minimum

15. Linux The routed daemon implemented dynamic routing based on RIP A modern replacement for routed is gated supports more protocols