Routing Protocols
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Transcript of Routing Protocols
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Routing ProtocolsBrandon Wagner
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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.
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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
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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.
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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
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Other Examples
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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.
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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?
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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.
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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.
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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.
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Routing Reviewed
Questions?