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2008 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialPresentation_ID 1
Chapter 4: RoutingConcepts
Routing & Switching
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Presentation_ID 2 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 4
4.0 Routing Concepts
4.1 Initial Configuration of a Router
4.2 Routing Decisions
4.3 Router Operation
4.4 Summary
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Presentation_ID 3 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 4: Objectives
Configure a router to route between multiple directly connectednetworks
Describe the primary functions and features of a router.
Explain how routers use information in data packets to makeforwarding decisions in a small- to medium-sized business network.
Explain the encapsulation and de-encapsulation process used byrouters when switching packets between interfaces.
Compare ways in which a router builds a routing table whenoperating in a small- to medium-sized business network.
Explain routing table entries for directly connected networks.
Explain how a router builds a routing table of directly connectednetworks.
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Presentation_ID 4 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 4: Objectives (cont.)
Explain how a router builds a routing table using static routes.
Explain how a router builds a routing table using a dynamic routingprotocol.
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Presentation_ID 5 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Functions of a Router
Characteristicsof a Network
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Presentation_ID 6 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Functions of a Router
Why Routing?
The router is responsible for the routing of trafficbetween networks.
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Presentation_ID 7 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Routers are specialized computers containing thefollowing required components to operate:
Central processing unit (CPU)
Operating system (OS) - Routers use Cisco IOS
Memory and storage (RAM, ROM, NVRAM, Flash, harddrive)
Functions of a Router
Routers are Computers
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Presentation_ID 8 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Routers use specialized ports and network interfacecards to interconnect to other networks.
Functions of a Router
Routers are Computers
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Presentation_ID 9 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Routers can connect multiple networks.
Routers have multiple interfaces, each on a differentIP network.
Functions of a Router
Routers Interconnect Networks
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Presentation_ID 10 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Functions of a Router
Routers Choose Best Paths
Routers use static routes and dynamic routing protocolsto learn about remote networks and build their routingtables.
Routers use routing tables to determine the best path tosend packets.
Routers encapsulate the packet and forward it to theinterface indicated in routing table.
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Presentation_ID 11 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Functions of a Router
Routers Choose Best Paths
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Presentation_ID 12 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Process switching An olderpacket forwarding mechanismstill available for Cisco routers.
Fast switching A commonpacket forwarding mechanismwhich uses a fast-switchingcache to store next hop
information.
Cisco Express Forwarding(CEF) The most recent,fastest, and preferred Cisco
IOS packet-forwardingmechanism. Table entries arenot packet-triggered like fastswitching but change-triggered.
Functions of a Router
Packet Forwarding Methods
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Presentation_ID 13 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Connect Devices
Connect to a Network
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Presentation_ID 14 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
To enable network accessdevices must be configuredwith the following IP addressinformation
IP address- Identifies aunique host on a localnetwork.
Subnet mask - Identifiesthe hosts networksubnet.
Default gateway -Identifies the router a
packet is sent to to whenthe destination is not onthe same local networksubnet.
Connect Devices
Default Gateways
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Presentation_ID 15 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Network Documentation should include at least the following in a topologydiagram and addressing table:
Device names
Interfaces
IP addresses and
subnet mask
Default gateways
Connect Devices
Document Network Addressing
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Presentation_ID 16 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Connect Devices
Enable IP on a Host
Statically Assigned IP address The host is manually assignedan IP address, subnet mask and default gateway. A DNS server IP
address can also be assigned. Used to identify specific network resources such as
network servers and printers.
Can be used in very small networks with few hosts.
Dynamically Assigned IP Address IP Address information isdynamically assigned by a server using Dynamic HostConfiguration Protocol (DHCP).
Most hosts acquire their IP address information throughDHCP.
DHCP services can be provided by Cisco routers.
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Presentation_ID 17 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Connect Devices
Device LEDs
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Presentation_ID 18 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Console access requires:
Console cable RJ-45-to-DB-9 console cable
Terminal emulation software Tera Term, PuTTY,HyperTerminal
Connect Devices
Console Access
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Presentation_ID 19 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Network infrastructure devices require IP addresses to enableremote management.
On a switch, the management IP address is assigned on avirtual interface.
Connect Devices
Enable IP on a Switch
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Presentation_ID 20 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Basics tasks that should be first configured on a Cisco Router andCisco Switch:
Name the device Distinguishes it from other routers
Secure management access Secures privileged EXEC, userEXEC, and Telnet access, and encrypts passwords to theirhighest level
Configure a banner Provides legal notification ofunauthorized access.
Save the Configuration
Basic Settings on a Router
Configure Basic Router Settings
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Presentation_ID 21 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
To be available, a routerinterface must be:
Configured with an address andsubnet mask .
Must be activated using noshutdown command. By defaultLAN and WAN interfaces arenot activated.
Serial cable end labeled DCEmust be configured with theclock rate command.
Optional description can beincluded.
Basic Settings on a Router
Configure an IPv4 Router Interface
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Presentation_ID 22 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
To configure interface with IPv6address and subnet mask:
Use the ipv6 address ipv6-address/ipv6-length [link-local | eui-64]interface configuration command.
Activate using the no shutdowncommand.
IPv6 interfaces can support more thanone address:
Configure a specified global unicast -ipv6-address/ipv6-length
Configure a global IPv6 address withan interface identifier (ID) in the low-order 64 bits - ipv6-address/ipv6-length eui-64
Configure a link-local address - ipv6-address/ipv6-length link-local
Basic Settings on a Router
Configure an IPv6 Router Interface
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Presentation_ID 23 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Basic Settings on a Router
Configure a Loopback InterfaceA loopback interface is alogical interface that isinternal to the router:
It is not assigned to aphysical port, it isconsidered a softwareinterface that is
automatically in an UPstate.
A loopback interface isuseful for testing.
It is important in the OSPFrouting process.
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Presentation_ID 24 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Verify Connectivity of Directly Connected Networks
Verify Interface Settings
Show commands are usedto verify operation and
configuration of interface:
show ip interfaces brief
show ip route
show running-config
Show commands are usedto gather more detailedinterface information:
show interfaces
show ip interfaces
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Presentation_ID 25 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Verify Connectivity of Directly Connected Networks
Verify Interface SettingsSome of the commoncommands to verify the IPv6interface configuration are:
show ipv6 interface brief -displays a summary for eachof the interfaces.
show ipv6 interface
gigabitethernet 0/0 -displays the interface statusand all the IPv6 addresses forthis interface.
show ipv6 route - verifies
that IPv6 networks andspecific IPv6 interfaceaddresses have beeninstalled in the IPv6 routingtable.
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Presentation_ID 26 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Show command output can be managed using the following command andfilters:
Use theterminal length number command to specify the number of linesto be displayed. A value of 0 (zero) prevents the router from pausingbetween screens of output.
To filter specific output of commands use the (|)pipe character after showcommand. Parameters that can be used after pipe include:
section, include, exclude, begin
Verify Connectivity of Directly Connected Networks
Filter Show Command Output
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Presentation_ID 27 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Verify Connectivity of Directly Connected Networks
Command History Feature
The command history feature temporarily stores a list of executed
commands for access:
To recall commands pressCtrl+P or the UP Arrow.
To return to more recent commands press Ctrl+N or theDownArrow.
By default, command history is enabled and the system capturesthe last 10 commands in the buffer. Use the show historyprivileged EXEC command to display the buffer contents.
Use the terminal history size user EXEC command to increase ordecrease size of the buffer.
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Presentation_ID 28 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Switching Packets between Networks
Router Switching Functions
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Presentation_ID 29 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Switching Packets between Networks
Send a Packet
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Presentation_ID 30 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Switching Packets between Networks
Forward to the Next HopJG1
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Slide 30
JG1 this graphic is from page 4.2.1.5, please replace with the graphic from 4.2.1.3Jane Gibbons, 10/9/2013
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Presentation_ID 31 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Switching Packets between Networks
Packet Routing
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Presentation_ID 32 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Switching Packets between Networks
Reach the Destination
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Presentation_ID 33 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Path Determination
Routing Decisions
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Presentation_ID 35 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Path Determination
Load BalancingWhen a router has two or more paths to a destination withequal cost metrics, then the router forwards the packets
using both paths equally:
Equal cost load balancing can improve networkperformance.
Equal cost load balancing can be configured to useboth dynamic routing protocols and static routes.
RIP, OSPF and EIGRP support equal cost load
balancing.
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Presentation_ID 37 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
The Routing Table
The Routing TableA routing table is a file stored in RAM that containsinformation about:
Directly connected routes
Remote routes
Network or next hop associations
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Presentation_ID 39 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
The Routing Table
Routing Table Sources
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Presentation_ID 40 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
The Routing Table
Remote Network Routing EntriesInterpreting the entries in the routing table.
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Presentation_ID 41 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Directly Connected Routes
Directly Connected InterfacesA newly deployed router, without any configured interfaces, has anempty routing table. An active, configured, directly connected interfacecreates two routing table entries:
Link Local (L)
Directly Connected (C)
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Presentation_ID 43 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Directly Connected Routes
Directly Connected IPv6 ExampleThe show ipv6 routecommand shows the ipv6 networks and routesinstalled in the routing table.
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Presentation_ID 44 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Statically Learned Routes
Static RoutesStatic routes and default static routes can be implemented afterdirectly connected interfaces are added to the routing table:
Static routes are manually configured
They define an explicit path between two networking devices.
Static routes must be manually updated if the topology changes.
Their benefits include improved security and control of resources. Configure a static route to a specific network using the ip route
network mask{next-hop-ip| exit-intf} command.
A default static route is used when the routing table does not contain
a path for a destination network.
Configure a default static route using the ip route 0.0.0.0
0.0.0.0 {exit-intf| next-hop-ip} command.
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Presentation_ID 46 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Statically Learned Routes
Static Routes Example
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Presentation_ID 47 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Statically Learned Routes
Static IPv6 Routes Example
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Presentation_ID 48 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Dynamic Routing Protocols
Dynamic RoutingDynamic routing is used by routers to share information about thereachability and status of remote networks. It performs networkdiscovery and maintains routing tables.
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Presentation_ID 50 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Dynamic Routing Protocols
IPv4 Routing Protocols
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Presentation_ID 51 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Dynamic Routing Protocols
IPv6 Routing ProtocolsCisco ISR routers can support a variety of dynamic IPv6 routingprotocols including:
RIPng -RIP next generation OSPFv3
EIGRPfor IPv6
MP-BGP4 -Multicast Protocol-Border Gateway Protocol
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Presentation_ID 52 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Dynamic Routing Protocols
IPv6 Routing Protocols
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Presentation_ID 53 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 4: Summary There are many key structures and performance-related
characteristics referred to when discussing networks: topology,speed, cost, security, availability, scalability, and reliability.
Cisco routers and Cisco switches have many similarities. Theysupport a similar modal operating system, similar commandstructures, and many of the same commands.
One distinguishing feature between switches and routers is the typeof interfaces supported by each.
The main purpose of a router is to connect multiple networks andforward packets from one network to the next. This means that arouter typically has multiple interfaces. Each interface is a memberor host on a different IP network.
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Presentation_ID 54 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 4: Summary (cont.) The routing table is a list of networks known by the router.
A remote network is a network that can only be reached by
forwarding the packet to another router. Remote networks are added to the routing table in two ways: either
by the network administrator manually configuring static routes or byimplementing a dynamic routing protocol.
Static routes do not have as much overhead as dynamic routingprotocols; however, static routes can require more maintenance ifthe topology is constantly changing or is unstable.
Dynamic routing protocols automatically adjust to changes without
any intervention from the network administrator. Dynamic routingprotocols require more CPU processing and also use a certainamount of link capacity for routing updates and messages.
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Presentation_ID 55 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
Chapter 4: Summary (cont.) Routers make their primary forwarding decision at Layer 3, the
Network layer. However, router interfaces participate in Layers 1, 2,and 3. Layer 3 IP packets are encapsulated into a Layer 2 data link
frame and encoded into bits at Layer 1.
Router interfaces participate in Layer 2 processes associated withtheir encapsulation. For example, an Ethernet interface on a routerparticipates in the ARP process like other hosts on that LAN.
Components of the IPv6 routing table are very similar to the IPv4routing table. For instance, it is populated using directly connectedinterfaces, static routes and dynamically learned routes.
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Presentation_ID 56 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential
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