Top-Down Network Design
Chapter Seven
Selecting Switching and Routing Protocols
Copyright 2010 Cisco Press & Priscilla Oppenheimer
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Selecting Switching and Routing Protocols for Network Design, Schemes and Mind Maps of Network Design
An in-depth analysis of various switching and routing protocols used in network design. It covers topics such as layer 2 transparent bridging, multilayer switching, spanning tree protocol enhancements, vlan technologies, static and dynamic routing, distance-vector and link-state protocols, and more. The document also discusses selection criteria for these protocols, including network traffic characteristics, bandwidth, memory and cpu usage, the number of peers supported, the capability to adapt to changes quickly, and support for authentication.
Typology: Schemes and Mind Maps
2023/2024
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Top-Down Network Design
Chapter Seven
Selecting Switching and Routing Protocols Copyright 2010 Cisco Press & Priscilla Oppenheimer
Switching and Routing Choices
- (^) Switching
- (^) Layer 2 transparent bridging (switching)
- (^) Multilayer switching
- (^) Spanning Tree Protocol enhancements
- (^) VLAN technologies
- (^) Routing
- (^) Static or dynamic
- (^) Distance-vector and link-state protocols
- (^) Interior and exterior
- (^) Etc.
Making Decisions
- (^) Goals must be established
- (^) Many options should be explored
- (^) The consequences of the decision should be investigated
- (^) Contingency plans should be made
- (^) A decision table can be used
Example Decision Table
Switching Table on a Bridge or
Switch
MAC Address Port 1 2 3 08-00-07-06-41-B 00-00-0C-60-7C- 00-80-24-07-8C-
Cisco Spanning Tree Protocol
Enhancements
- (^) PortFast
- (^) UplinkFast and Backbone Fast
- (^) Unidirectional link detection
- (^) Loop Guard
Protocols for Transporting
VLAN Information
- (^) Inter-Switch Link (ISL)
- (^) Tagging protocol
- (^) Cisco proprietary
- (^) IEEE 802.1Q
- (^) Tagging protocol
- (^) IEEE standard
- (^) VLAN Trunk Protocol (VTP)
- (^) VLAN management protocol
Selecting Routing Protocols
- (^) They all have the same general goal:
- (^) To share network reachability information among routers
- (^) They differ in many ways:
- (^) Interior versus exterior
- (^) Metrics supported
- (^) Dynamic versus static and default
- (^) Distance-vector versus link-sate
- (^) Classful versus classless
- (^) Scalability
Routing Protocol Metrics
- (^) Metric: the determining factor used by a routing algorithm to decide which route to a network is better than another
- (^) Examples of metrics:
- (^) Bandwidth - capacity
- (^) Delay - time
- (^) Load - amount of network traffic
- (^) Reliability - error rate
- (^) Hop count - number of routers that a packet must travel through before reaching the destination network
- (^) Cost - arbitrary value defined by the protocol or administrator
Routing Algorithms
- (^) Static routing
- (^) Calculated beforehand, offline
- (^) Default routing
- (^) “If I don’t recognize the destination, just send the packet to Router X”
- (^) Cisco’s On-Demand Routing
- (^) Routing for stub networks
- (^) Uses Cisco Discovery Protocol (CDP)
- (^) Dynamic routing protocol
- (^) Distance-vector algorithms
- (^) Link-state algorithms
Default Routing Example
RouterA(config)# ip route 0.0.0.0 0.0.0.0 172.16.20. If it’s not local, send it to 172.16.20.2 (Router B) e0 e0 e s0 s s0 s Router A Router B Router C Host A Host B Host C 172.16.10.2 172.16.30.2 172.16.50. 172.16.20.1 172.16.40. 172.16.10.1 172.16.30.1 172.16.50. 172.16.20.2 172.16.40.
Distance-Vector Routing
- (^) Router maintains a routing table that lists known networks, direction (vector) to each network, and the distance to each network
- (^) Router periodically (every 30 seconds, for example) transmits the routing table via a broadcast packet that reaches all other routers on the local segments
- (^) Router updates the routing table, if necessary, based on received broadcasts
Link-State Routing
- (^) Routers send updates only when there’s a change
- (^) Router that detects change creates a link-state advertisement (LSA) and sends it to neighbors
- (^) Neighbors propagate the change to their neighbors
- (^) Routers update their topological database if necessary
Distance-Vector Vs. Link-State
- (^) Distance-vector algorithms keep a list of networks, with next hop and distance (metric) information
- (^) Link-state algorithms keep a database of routers and links between them - (^) Link-state algorithms think of the internetwork as a graph instead of a list - (^) When changes occur, link-state algorithms apply Dijkstra’s shortest-path algorithm to find the shortest path between any two nodes