Brandon Wagner
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.
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
Two Types
 Interior 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.
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

Examples


OSPF – Open Shortest Path First
IS-IS – Intermediate System to Intermediate System
Other Examples
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.
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?
Link-State: OSPF
 Mechanism:
 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.
Distance-Vector vs Link-State
 Distance Vector
 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
 Pro’s


Each router has a full network topology.
Convergence after a topology change is quicker.
 Con’s
 Requires more processing power and memory.
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.
Routing Reviewed
Questions?