1. Routing Protocols
Brandon Wagner

2. Learning Outcomes
Understand Interior and External Routing protocols and their differences
Understand Distance-Vector and Link-State routing methods
Describe the routing mechanisms of common routing protocols.

3. What does a Routing Protocol do?
Determine the best forwarding path from point A to point B.
Prevent routing loops.
Builds a routing table.
Destination and gateway

4. Two Types Interior Gateway Protocol Exterior Gateway Protocol
Routing within an Autonomous System (AS)
Exterior Gateway Protocol
Routing between Autonomous System’s.
Autonomous System
Group of IP networks controlled by a single common administrator.
Managed by IANA (Internet Assigned Numbers Authority)
BYU has 1 assigned AS number.

5. IGP: Interior Gateway Protocols
Distance-Vector Routing Protocol
Distance – the cost of reaching the destination.
Vector – direction (which interface) to forward traffic.
Information is only exchanged with neighbors.
Examples
RIP – Routing Information Protocol
EIGRP – Enhanced Interior Gateway Routing Protocol
Link-State Routing Protocol
Link – the speed of the link (10 Meg / 100 Meg / 1 Gb / 10 Gb)
State – Is the interface up or down?
The whole network topology is known by every router
OSPF – Open Shortest Path First
IS-IS – Intermediate System to Intermediate System

6. Other Examples

7. Distance-Vector: RIP
Mechanism: Each router sends routing table to neighbor. Neighbor then forwards routing table to it’s neighbor.
Algorithm: Bellman-Ford
First Deployed: 1967
Cost: Hop Count
Maximum # of hops is 15.
Best Fit: Small networks with minimal changes.

8. Distance-Vector: EIGRP
Mechanism:
Neighbor Table – List of all directly connected neighbors
Topology Table – all available destination routes from neighbors
Route Table – built from applying metric formula to Topology Table
First Deployed: 1995
Cost: Delay, Bandwidth, Reliability, Load
Best Fit: Enterprise Architecture Model
Packet Types: Update, Query, Reply, Hello
Sometimes called Hybrid – why?

9. Link-State: OSPF Mechanism: Algorithm: Dijkstra’s
Link State Advertisements (LSA) sent out to all other routers.
Each router builds a LSDB
The Database is converted into a weight graph.
Each router determines shortest path to each other.
Algorithm: Dijkstra’s
Cost: Definable – bandwidth is commonly used.
Best Fit: Very, very, VERY large networks.
Split into network areas to reduce the size of update packets.

10. Distance-Vector vs Link-State
Pro’s
Only have receive updates from neighbors.
Simple to use and smaller overhead.
Con’s
Updates are spread node-by-node.
Count-to-infinity problem.
Link State
Each router has a full network topology.
Convergence after a topology change is quicker.
Requires more processing power and memory.

11. EGP: Exterior Gateway Protocol
BGP – Border Gateway Protocol
Routes the internet
The full route table is currently 357,000 path entries
Path-Vector Routing Algorithm
Tracks paths according to AS.
Local preference determine best path to destination network. (Border Example)
Does NOT track routes through individual routers.

12. Routing Reviewed
Questions?