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SWITCHING AND ROUTING Presentation Transcript
1.SWITCHING AND ROUTING
2.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.
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.
3.Selection Criteria for Switching & Routing Protocols
Network traffic characteristics
Bandwidth, memory, and CPU usage
The number of peers supported
The capability to adapt to changes quickly
Support for authentication
Network traffic characteristics
Bandwidth, memory, and CPU usage
The number of peers supported
The capability to adapt to changes quickly
Support for authentication
4.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
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
5.Example Decision Table
6.Transparent Bridging (Switching) Tasks
Forward frames transparently
Learn which port to use for each MAC address
Flood frames when the destination unicast address hasn’t been learned yet
Filter frames from going out ports that don’t include the destination address
Flood broadcasts and multicasts
Forward frames transparently
Learn which port to use for each MAC address
Flood frames when the destination unicast address hasn’t been learned yet
Filter frames from going out ports that don’t include the destination address
Flood broadcasts and multicasts
7.Switching Table on a Bridge or Switch
8.Cisco Spanning Tree Protocol Enhancements
PortFast
UplinkFast and Backbone Fast
Unidirectional link detection
Loop Guard
PortFast
UplinkFast and Backbone Fast
Unidirectional link detection
Loop Guard
9.Redundant Uplinks
10.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
Inter-Switch Link (ISL)
Tagging protocol
Cisco proprietary
IEEE 802.1Q
Tagging protocol
IEEE standard
VLAN Trunk Protocol (VTP)
VLAN management protocol
11.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
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
12.Interior Versus Exterior Routing Protocols
Interior routing protocols are used within an autonomous system
Exterior routing protocols are used between autonomous systems
Interior routing protocols are used within an autonomous system
Exterior routing protocols are used between autonomous systems
13.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
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
14.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
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
15.Static Routing Example
16.Default Routing Example
17.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
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
18.Distance-Vector Routing Tables
19.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
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
20.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
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
21.Choosing Between Distance-Vector and Link-State
Choose Distance-Vector
Simple, flat topology
Hub-and-spoke topology
Junior network administrators
Convergence time not a big concern
Choose Distance-Vector
Simple, flat topology
Hub-and-spoke topology
Junior network administrators
Convergence time not a big concern
22.Dynamic IP Routing Protocols
Distance-Vector
Routing Information Protocol (RIP) Version 1 and 2
Interior Gateway Routing Protocol (IGRP)
Enhanced IGRP
Border Gateway Protocol (BGP)
Distance-Vector
Routing Information Protocol (RIP) Version 1 and 2
Interior Gateway Routing Protocol (IGRP)
Enhanced IGRP
Border Gateway Protocol (BGP)
23.Routing Information Protocol (RIP)
First standard routing protocol developed for TCP/IP environments
RIP Version 1 is documented in RFC 1058 (1988)
RIP Version 2 is documented in RFC 2453 (1998)
Easy to configure and troubleshoot
Broadcasts its routing table every 30 seconds; 25 routes per packet
Uses a single routing metric (hop count) to measure the distance to a destination network; max hop count is 15
First standard routing protocol developed for TCP/IP environments
RIP Version 1 is documented in RFC 1058 (1988)
RIP Version 2 is documented in RFC 2453 (1998)
Easy to configure and troubleshoot
Broadcasts its routing table every 30 seconds; 25 routes per packet
Uses a single routing metric (hop count) to measure the distance to a destination network; max hop count is 15
24.RIP V2 Features
Includes the subnet mask with route updates
Supports prefix routing (classless routing, supernetting)
Supports variable-length subnet masking (VLSM)
Includes simple authentication to foil crackers sending routing updates
Includes the subnet mask with route updates
Supports prefix routing (classless routing, supernetting)
Supports variable-length subnet masking (VLSM)
Includes simple authentication to foil crackers sending routing updates
25.IGRP Solved Problems with RIP
15-hop limitation in RIP
IGRP supports 255 hops
Reliance on just one metric (hop count)
IGRP uses bandwidth, delay, reliability, load
(By default just uses bandwidth and delay)
RIP's 30-second update timer
IGRP uses 90 seconds
15-hop limitation in RIP
IGRP supports 255 hops
Reliance on just one metric (hop count)
IGRP uses bandwidth, delay, reliability, load
(By default just uses bandwidth and delay)
RIP's 30-second update timer
IGRP uses 90 seconds
26.EIGRP
Adjusts to changes in internetwork very quickly
Incremental updates contain only changes, not full routing table
Updates are delivered reliably
Router keeps track of neighbors’ routing tables and uses them as feasible successor
Same metric as IGRP, but more granularity (32 bits instead of 24 bits)
Adjusts to changes in internetwork very quickly
Incremental updates contain only changes, not full routing table
Updates are delivered reliably
Router keeps track of neighbors’ routing tables and uses them as feasible successor
Same metric as IGRP, but more granularity (32 bits instead of 24 bits)
27.Open Shortest Path First (OSPF)
Open standard, defined in RFC 2328
Adjusts to changes quickly
Supports very large internetworks
Does not use a lot of bandwidth
Authenticates protocol exchanges to meet security goals
Open standard, defined in RFC 2328
Adjusts to changes quickly
Supports very large internetworks
Does not use a lot of bandwidth
Authenticates protocol exchanges to meet security goals
28.OSPF Metric
A single dimensionless value called cost. A network administrator assigns an OSPF cost to each router interface on the path to a network. The lower the cost, the more likely the interface is to be used to forward data traffic.
On a Cisco router, the cost of an interface defaults to 100,000,000 divided by the bandwidth for the interface. For example, a 100-Mbps Ethernet interface has a cost of 1.
A single dimensionless value called cost. A network administrator assigns an OSPF cost to each router interface on the path to a network. The lower the cost, the more likely the interface is to be used to forward data traffic.
On a Cisco router, the cost of an interface defaults to 100,000,000 divided by the bandwidth for the interface. For example, a 100-Mbps Ethernet interface has a cost of 1.
29.OSPF Areas Connected via Area Border Routers (ABRs)
30.IS-IS
Intermediate System-to-Intermediate System
Link-state routing protocol
Designed by the ISO for the OSI protocols
Integrated IS-IS handles IP also
Intermediate System-to-Intermediate System
Link-state routing protocol
Designed by the ISO for the OSI protocols
Integrated IS-IS handles IP also
31.Border Gateway Protocol (BGP)
Allows routers in different autonomous systems to exchange routing information
Exterior routing protocol
Used on the Internet among large ISPs and major companies
Supports route aggregation
Main metric is the length of the list of autonomous system numbers, but BGP also supports routing based on policies
Allows routers in different autonomous systems to exchange routing information
Exterior routing protocol
Used on the Internet among large ISPs and major companies
Supports route aggregation
Main metric is the length of the list of autonomous system numbers, but BGP also supports routing based on policies
32.Summary
The selection of switching and routing protocols should be based on an analysis of
Goals
Scalability and performance characteristics of the protocols
Transparent bridging is used on modern switches
But other choices involve enhancements to STP and protocols for transporting VLAN information
There are many types of routing protocols and many choices within each type
The selection of switching and routing protocols should be based on an analysis of
Goals
Scalability and performance characteristics of the protocols
Transparent bridging is used on modern switches
But other choices involve enhancements to STP and protocols for transporting VLAN information
There are many types of routing protocols and many choices within each type
33.Review Questions
What are some options for enhancing the Spanning Tree Protocol?
What factors will help you decide whether distance-vector or link-state routing is best for your design customer?
What factors will help you select a specific routing protocol?
Why do static and default routing still play a role in many modern network designs?
What are some options for enhancing the Spanning Tree Protocol?
What factors will help you decide whether distance-vector or link-state routing is best for your design customer?
What factors will help you select a specific routing protocol?
Why do static and default routing still play a role in many modern network designs?
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