Routing Protocols Brandon Wagner.

Routing ProtocolsBrandon Wagner

Learning OutcomesUnderstand 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: RIPMechanism: Each router sends routing

table to neighbor. Neighbor then forwards routing table to it’s neighbor.

Algorithm: Bellman-Ford

First Deployed: 1967

Cost: Hop CountMaximum # 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-StateDistance 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 ProtocolBGP – 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?