Redes de
Computadores (11558)
Ano Lectivo 2014/2015 * 1º Semestre
!
Licenciatura em
Engenharia Informática
!
Aula 9 01/12/2014
!
UNIVERSIDADE DA BEIRA INTERIOR
!
Faculdade de Engenharia
Departamento de Informática
1
Nuno M. Garcia, ngarcia@di.ubi.pt
Redes de Computadores
• Agenda
•• Routing e Static Routing
• outros assuntos?
(adaptado do capítulo 1 e capítulo 2 do curso CCNA2 da Academia Cisco da UBI)
!
UNIVERSIDADE DA BEIRA INTERIOR
!
Faculdade de Engenharia
Departamento de Informática
2
Nuno M. Garcia, ngarcia@di.ubi.pt
Chapter 1: Routing
Concepts
Routing Protocols
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 1
1.0 Routing Concepts
1.1 Initial Configuration of a Router
1.2 Routing Decisions
1.3 Router Operation
1.4 Summary
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 1: Objectives
▪ Configure a router to route between multiple directly connected
networks
▪ Describe the primary functions and features of a router.
▪ Explain how routers use information in data packets to make
forwarding decisions in a small- to medium-sized business network.
▪ Explain the encapsulation and de-encapsulation process used by
routers when switching packets between interfaces.
▪ Compare ways in which a router builds a routing table when operating
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 connected
networks.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 1: Objectives (cont.)
▪ Explain how a router builds a routing table using static routes.
▪ Explain how a router builds a routing table using a dynamic routing
protocol.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Functions of a Router
Characteristics of a Network
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Functions of a Router
Why Routing?
The router is responsible for the routing of traffic
between networks.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Functions of a Router
Routers are Computers
Routers are specialized computers containing the
following required components to operate:
• Central processing unit (CPU)
• Operating system (OS) - Routers use Cisco IOS
• Memory and storage (RAM, ROM, NVRAM, Flash, hard drive)
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Functions of a Router
Routers are Computers
Routers use specialized ports and network interface
cards to interconnect to other networks.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Functions of a Router
Routers Interconnect Networks
▪ Routers can connect multiple networks.
▪ Routers have multiple interfaces, each on a different IP network.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Functions of a Router
Routers Choose Best Paths
▪ Routers use static routes and dynamic routing
protocols to learn about remote networks and build
their routing tables.
▪ Routers use routing tables to determine the best path
to send packets.
▪ Routers encapsulate the packet and forward it to the
interface indicated in routing table.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Functions of a Router
Routers Choose Best Paths
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Functions of a Router
Packet Forwarding Methods
▪ Process switching – An older
packet forwarding mechanism
still available for Cisco routers.
▪ Fast switching – A common
packet forwarding mechanism
which uses a fast-switching
cache to store next hop
information.
▪ Cisco Express Forwarding
(CEF) – The most recent,
fastest, and preferred Cisco IOS
packet-forwarding mechanism.
Table entries are not packettriggered like fast switching but
change-triggered.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Connect Devices
Connect to a Network
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Connect Devices
Default Gateways
To enable network access
devices must be configured with
the following IP address
information
▪IP address - Identifies a
unique host on a local
network.
▪Subnet mask - Identifies the
host’s network subnet.
▪Default gateway - Identifies
the router a packet is sent to
to when the destination is not
on the same local network
subnet.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Connect Devices
Document Network Addressing
Network Documentation should include at least the following in a topology
diagram and addressing table:
▪ Device names
▪ Interfaces
▪ IP addresses and
subnet mask
▪ Default gateways
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Connect Devices
Enable IP on a Host
Statically Assigned IP address – The host is manually assigned
an 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 is
dynamically assigned by a server using Dynamic Host Configuration
Protocol (DHCP).
• Most hosts acquire their IP address information through
DHCP.
• DHCP services can be provided by Cisco routers.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Connect Devices
Device LEDs
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Connect Devices
Console Access
Console access requires:
• Console cable – RJ-45-to-DB-9 console cable
• Terminal emulation software – Tera Term, PuTTY,
HyperTerminal
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Connect Devices
Enable IP on a Switch
▪ Network infrastructure devices require IP addresses to enable
remote management.
▪ On a switch, the management IP address is assigned on a virtual
interface.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Basic Settings on a Router Configure Basic Router Settings
Basics tasks that should be first configured on a Cisco Router and
Cisco Switch:
▪ Name the device – Distinguishes it from other routers
▪ Secure management access – Secures privileged EXEC, user
EXEC, and Telnet access, and encrypts passwords to their
highest level
!
!
!
!
▪ Configure a banner – Provides legal notification of unauthorized
access.
▪ Save the Configuration
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Basic Settings on a Router Configure an IPv4 Router Interface
To be available, a router
interface must be:
▪ Configured with an address and
subnet mask .
▪ Must be activated using no
shutdown command. By default
LAN and WAN interfaces are not
activated.
▪ Serial cable end labeled DCE must
be configured with the clock
rate command.
▪ Optional description can be
included.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Basic Settings on a Router Configure an IPv6 Router Interface
To configure interface with IPv6 address
and subnet mask:
▪ Use the ipv6 address ipv6-address/ipv6length [link-local | eui-64]interface
configuration command.
▪ Activate using the no shutdown command.
IPv6 interfaces can support more than
one address:
▪ Configure a specified global unicast - ipv6address /ipv6-length
▪ Configure a global IPv6 address with an
interface identifier (ID) in the low-order 64
bits - ipv6-address /ipv6-length eui-64
▪ Configure a link-local address - ipv6address /ipv6-length link-local
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Basic Settings on a Router Configure a Loopback Interface
A loopback interface is a
logical interface that is
internal to the router:
▪ It is not assigned to a
physical port, it is
considered a software
interface that is automatically
in an UP state.
▪ A loopback interface is
useful for testing.
▪ It is important in the OSPF
routing process.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Verify Connectivity of Directly Connected Networks Verify Interface Settings
Show commands are used to
verify operation and
configuration of interface:
▪ show ip interfaces brief
▪ show ip route
▪ show running-config
Show commands are used to
gather more detailed
interface information:
▪ show interfaces
▪ show ip interfaces
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Verify Connectivity of Directly Connected Networks Verify Interface Settings
Some of the common commands
to verify the IPv6 interface
configuration are:
▪ show ipv6 interface brief displays a summary for each of
the interfaces.
▪ show ipv6 interface
gigabitethernet 0/0 - displays
the interface status and all the
IPv6 addresses for this
interface.
▪ show ipv6 route - verifies that
IPv6 networks and specific IPv6
interface addresses have been
installed in the IPv6 routing
table.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Verify Connectivity of Directly Connected Networks Filter Show Command Output
Show command output can be filtered using the following command and filters:
▪ Use the terminal length number command to specify the number of lines to be
displayed. A value of 0 (zero) prevents the router from pausing between screens
of output.
▪ To filter specific output of commands use the (|)pipe character after show
command. Parameters that can be used after pipe include:
section, include, exclude, begin
Presentation_ID
© 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 press Ctrl+P or the UP Arrow.
▪ To return to more recent commands press Ctrl+N or the Down
Arrow.
▪ By default, command history is enabled and the system captures the
last 10 commands in the buffer. Use the show history privileged
EXEC command to display the buffer contents.
▪ Use the terminal history size user EXEC command to increase or
decrease size of the buffer.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Switching Packets between Networks
Router Switching Functions
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Switching Packets between Networks
Send a Packet
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Switching Packets between Networks Forward to the Next Hop
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Switching Packets between Networks Packet Routing
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Switching Packets between Networks Reach the Destination
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Path Determination
Routing Decisions
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Path Determination
Best Path
Best path is selected by a routing protocol based on
the value or metric it uses to determine the distance to
reach a network:
▪ A metric is the value used to measure the distance to a given network.
▪ Best path to a network is the path with the lowest metric.
Dynamic routing protocols use their own rules and
metrics to build and update routing tables:
▪ Routing Information Protocol (RIP) - Hop count
▪ Open Shortest Path First (OSPF) - Cost based on cumulative
bandwidth from source to destination
▪ Enhanced Interior Gateway Routing Protocol (EIGRP) - Bandwidth,
delay, load, reliability
!
!
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Path Determination
Load Balancing
When a router has two or more paths to a destination with
equal cost metrics, then the router forwards the packets
using both paths equally:
• Equal cost load balancing can improve network
performance.
• Equal cost load balancing can be configured to use both
dynamic routing protocols and static routes.
• RIP, OSPF and EIGRP support equal cost load
balancing.
!
!
!
!
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Path Determination of the route
Administrative Distance
If multiple paths to a destination are configured on a router, the path
installed in the routing table is the one with the lowest Administrative
Distance (AD):
• A static route with an AD of 1 is more reliable than an EIGRPdiscovered route with an AD of 90.
• A directly connected route with an AD of 0 is more reliable than a
static route with an AD of 1.
!
!
!
!
!
!
Presentation_ID
!
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
The Routing Table
The Routing Table
A routing table is a file stored in RAM that contains
information about:
▪ Directly connected routes
▪ Remote routes
▪ Network or next hop associations
!
!
!
!
!
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
The Routing Table
Routing Table Sources
The show ip route command is used to display the
contents of the routing table:
▪ Local route interfaces - Added to the routing table when
an interface is configured. (displayed in IOS 15 or newer)
▪ Directly connected interfaces - Added to the routing
table when an interface is configured and active.
▪ Static routes - Added when a route is manually
configured and the exit interface is active.
▪ Dynamic routing protocol - Added when EIGRP or
OSPF are implemented and networks are identified.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
The Routing Table
Routing Table Sources
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
The Routing Table
Remote Network Routing Entries
Interpreting the entries in the routing table.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Directly Connected Routes
Directly Connected Interfaces
A newly deployed router, without any configured interfaces, has an empty
routing table. An active, configured, directly connected interface creates
two routing table entries:
▪ Link Local (L)
▪ Directly Connected (C)
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Directly Connected Routes
Directly Connected Example
A routing table with
the directly connected
interfaces of R1
configured and
activated.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Directly Connected Routes
Directly Connected IPv6 Example
The show ipv6 route command shows the ipv6 networks and routes
installed in the routing table.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Statically Learned Routes Static Routes
Static routes and default static routes can be implemented after
directly 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 {exitintf | next-hop-ip} command.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Statically Learned Routes Default Static Routes Example
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Statically Learned Routes Static Routes Example
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Statically Learned Routes Static IPv6 Routes Example
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Dynamic Routing Protocols
Dynamic Routing
Dynamic routing is used by routers to share information about the
reachability and status of remote networks. It performs network discovery
and maintains routing tables.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Dynamic Routing Protocols
IPv4 Routing Protocols
Cisco ISR routers can support a variety of dynamic IPv4
routing protocols including:
▪ EIGRP – Enhanced Interior Gateway Routing Protocol
▪ OSPF – Open Shortest Path First
▪ IS-IS – Intermediate System-to-Intermediate System
▪ RIP – Routing Information Protocol
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Dynamic Routing Protocols
IPv4 Routing Protocols
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Dynamic Routing Protocols
IPv6 Routing Protocols
Cisco ISR routers can support a variety of dynamic IPv6 routing protocols
including:
▪ RIPng - RIP next generation
▪ OSPFv3
▪ EIGRP for IPv6
▪ MP-BGP4 - Multicast Protocol-Border Gateway Protocol
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Dynamic Routing Protocols
IPv6 Routing Protocols
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 1: Summary
▪ This chapter introduced the router. The main purpose of a router is to
connect multiple networks and forward packets from one network to
the next.
▪ 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 one of two ways:
either by the network administrator manually configuring static routes
or by implementing a dynamic routing protocol.
▪ In many cases, a routing table will contain both static and dynamic
routes.
▪ Components of the IPv6 routing table are very similar to the IPv4
routing table. For instance, it is populated using directly connected
interfaces, static routes and dynamically learned routes.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 2: Static
Routing
Routing Protocols
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 2
2.1 Static Routing Implementation
2.2 Configure Static and Default Routes
2.3 Review of CIDR and VLSM
2.4 Configure Summary and Floating Static Routes
2.5 Troubleshoot Static and Default Route Issues
2.6 Summary
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 2: Objectives
▪ Explain the advantages and disadvantages of static
routing.
▪ Explain the purpose of different types of static routes.
▪ Configure IPv4 and IPv6 static routes by specifying a nexthop address.
▪ Configure an IPv4 and IPv6 default routes.
▪ Explain the use of legacy classful addressing in network
implementation.
▪ Explain the purpose of CIDR in replacing classful
addressing.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 2: Objectives (cont.)
▪ Design and implement a hierarchical addressing scheme.
▪ Configure an IPv4 and IPv6 summary network address to
reduce the number of routing table updates.
▪ Configure a floating static route to provide a backup
connection.
▪ Explain how a router processes packets when a static
route is configured.
▪ Troubleshoot common static and default route
configuration issues.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Static Routing
Reach Remote Networks
A router can learn about remote networks in one of two
ways:
• Manually - Remote networks are manually entered
into the route table using static routes.
• Dynamically - Remote routes are automatically
learned using a dynamic routing protocol.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Static Routing
Why Use Static Routing?
Static routing provides some advantages over dynamic
routing, including:
▪ Static routes are not advertised over the network,
resulting in better security.
▪ Static routes use less bandwidth than dynamic routing
protocols, no CPU cycles are used to calculate and
communicate routes.
▪ The path a static route uses to send data is known.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Static Routing
Why Use Static Routing? (cont.)
Static routing has the following disadvantages:
▪ Initial configuration and maintenance is time-consuming.
▪ Configuration is error-prone, especially in large
networks.
▪ Administrator intervention is required to maintain
changing route information.
▪ Does not scale well with growing networks; maintenance
becomes cumbersome.
▪ Requires complete knowledge of the whole network for
proper implementation.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Static Routing
When to Use Static Routes
Static routing has three primary uses:
▪ Providing ease of routing table maintenance in smaller
networks that are not expected to grow significantly.
▪ Routing to and from stub networks. A stub network is a
network accessed by a single route, and the router has
no other neighbors.
▪ Using a single default route to represent a path to any
network that does not have a more specific match with
another route in the routing table. Default routes are
used to send traffic to any destination beyond the next
upstream router.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Types of Static Routes
Static Route Applications
Static Routes are often used to:
▪ Connect to a specific network.
▪ Provide a Gateway of Last Resort for a stub network.
▪ Reduce the number of routes advertised by
summarizing several contiguous networks as one static
route.
▪ Create a backup route in case a primary route link fails.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Types of Static Routes
Standard Static Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Types of Static Routes
Default Static Route
▪ A default static route is a route that matches all packets.
▪ A default route identifies the gateway IP address to
which the router sends all IP packets that it does not
have a learned or static route.
▪ A default static route is simply a static route with
0.0.0.0/0 as the destination IPv4 address.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Types of Static Routes
Summary Static Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Types of Static Routes
Floating Static Route
▪ Floating static routes are static routes that are used to provide a
backup path to a primary static or dynamic route, in the event of a
link failure.
▪ The floating static route is only used when the primary route is not
available.
▪ To accomplish
this, the floating static route is configured with a higher administrative distance than the primary
route.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Static Routes
ip route Command
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Static Routes
Next-Hop Options
The next hop can be identified by an IP address, exit
interface, or both. How the destination is specified creates
one of the three following route types:
▪ Next-hop route - Only the next-hop IP address is
specified.
▪ Directly connected static route - Only the router exit
interface is specified.
▪ Fully specified static route - The next-hop IP address
and exit interface are specified.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Static Routes
Configure a Next-Hop Static Route
When a packet is destined for the 192.168.2.0/24 network, R1:
1. Looks for a match in the routing table and finds that it has to forward
the packets to the next-hop IPv4 address 172.16.2.2.
2. R1 must now determine how
to reach 172.16.2.2; therefore, it searches a second time for a
172.16.2.2 match.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Static Routes
Configure Directly Connected Static Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Static Routes
Configure a Fully Specified Static Route
In a fully specified static route:
▪ Both the output interface and the next-hop IP address
are specified.
▪ This is another type of static route that is used in older
IOSs, prior to CEF.
▪ This form of static route is used when the output
interface is a multi-access interface and it is necessary
to explicitly identify the next hop.
▪ The next hop must be directly connected to the specified
exit interface.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Static Routes
Verify a Static Route
Along with ping and traceroute, useful commands to
verify static routes include:
▪ show ip route!
▪ show ip route static!
▪ show ip route network
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Default Routes
Default Static Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Default Routes
Configure a Default Static Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Default Routes
Verify a Default Static Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Static Routes
The ipv6 route Command
Most of parameters are identical to the IPv4 version of the
command. IPv6 static routes can also be implemented as:
▪ Standard IPv6 static route
▪ Default IPv6 static route
▪ Summary IPv6 static route
▪ Floating IPv6 static route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Static Routes
Next-Hop Options
The next hop can be identified by an IPv6 address, exit
interface, or both. How the destination is specified creates
one of three route types:
▪ Next-hop IPv6 route - Only the next-hop IPv6 address
is specified.
▪ Directly connected static IPv6 route - Only the router
exit interface is specified.
▪ Fully specified static IPv6 route - The next-hop IPv6
address and exit interface are specified.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Static Routes
Configure a Next-Hop Static IPv6 Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Static Routes
Configure Directly Connected Static IPv6 Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Static Routes
Configure Fully Specified Static IPv6 Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Static Routes
Verify IPv6 Static Routes
Along with ping and traceroute, useful commands to
verify static routes include:
▪ show ipv6 route!
▪ show ipv6 route static!
▪ show ipv6 route network
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Default Routes
Default Static IPv6 Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Default Routes
Configure a Default Static IPv6 Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Default Routes
Verify a Default Static Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Classful Addressing
Classful Network Addressing
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Classful Addressing
Classful Subnet Masks
Class A
Class B
Class C
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Classful Addressing
Classful Routing Protocol Example
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Classful Addressing
Classful Addressing Waste
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
CIDR
Classless Inter-Domain Routing
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
CIDR
CIDR and Route Summarization
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
CIDR
Static Routing CIDR Example
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
CIDR
Classless Routing Protocol Example
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
VLSM
Fixed Length Subnet Masking
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
VLSM
Variable Length Subnet Masking
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
VLSM
VLSM in Action
VLSM allows the use of different masks for each subnet:
▪ After a network address is subnetted, those subnets can
be further subnetted.
▪ VLSM is simply subnetting a subnet. VLSM can be
thought of as sub-subnetting.
▪ Individual host addresses are assigned from the
addresses of "sub-subnets".
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
VLSM
Subnetting Subnets
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
VLSM
VLSM Example
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Summary Routes
Route Summarization
Route summarization, also known as route aggregation, is
the process of advertising a contiguous set of addresses
as a single address with a less-specific, shorter subnet
mask:
▪ CIDR is a form of route summarization and is
synonymous with the term supernetting.
▪ CIDR ignores the limitation of classful boundaries, and
allows summarization with masks that are smaller than
that of the default classful mask.
▪ This type of summarization helps reduce the number of
entries in routing updates and lowers the number of
entries in local routing tables.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Summary Routes
Calculate a Summary Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv4 Summary Routes
Summary Static Route Example
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Summary Routes
Summarize IPv6 Network Addresses
▪ Aside from the fact that IPv6 addresses are 128 bits
long and written in hexadecimal, summarizing IPv6
addresses is actually similar to the summarization of
IPv4 addresses. It just requires a few extra steps due to
the abbreviated IPv6 addresses and hex conversion.
▪ Multiple static IPv6 routes can be summarized into a
single static IPv6 route if:
• The destination networks are contiguous and can be
summarized into a single network address.
• The multiple static routes all use the same exit interface or nexthop IPv6 address.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Summary Routes
Calculate IPv6 Network Addresses
There are seven steps to summarize IPv6 networks into a single IPv6
prefix:
Step 1. List the network addresses (prefixes) and identify the part
where the addresses differ.
Step 2. Expand the IPv6 if it is abbreviated.
Step 3. Convert the differing section from hex to binary.
Step 4. Count the number of far left matching bits to determine the
prefix-length for the summary route.
Step 5. Copy the matching bits and then add zero bits to determine the
summarized network address (prefix).
Step 6. Convert the binary section back to hex.
Step 7. Append the prefix of the summary route (result of Step 4).
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure IPv6 Summary Routes
Configure an IPv6 Summary Address
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure Floating Static Routes
Floating Static Routes
Floating static routes are static routes that have an
administrative distance greater than the administrative
distance of another static route or dynamic routes:
▪ The administrative distance of a static route can be increased to
make the route less desirable than that of another static route or a
route learned through a dynamic routing protocol.
▪ In this way, the static route “floats” and is not used when the route
with the better administrative distance is active.
▪ However, if the preferred route is lost, the floating static route can
take over, and traffic can be sent through this alternate route.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure Floating Static Routes
Configure a Floating Static Route
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Configure Floating Static Routes
Test the Floating Static Route
To test a floating static route:
▪ Use a show ip route command to verify that the routing table is
using the default static route.
▪ Use a traceroute command to follow the traffic flow out the
primary route.
▪ Disconnect the primary link or shutdown the primary exit interface.
▪ Use a show ip route command to verify that the routing table is
using the floating static route.
▪ Use a traceroute command to follow the traffic flow out the
backup route.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Troubleshoot Static and Default Route Issues
Static Routes and Packet Forwarding
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Troubleshoot Static and Default Route Issues
Static Routes and Packet Forwarding (cont.)
▪ 1. The packet arrives on the interface GigabitEthernet 0/0 of R1.
▪ 2. R1 does not have a specific route to the destination network,
192.168.2.0/24; therefore, R1 uses the default static route.
▪ 3. R1 encapsulates the packet in a new frame. Because the link to R2 is
a point-to-point link, R1 adds an "all 1s" address for the Layer 2
destination address.
▪ 4. The frame is forwarded out of the Serial 0/0/0 interface. The packet
arrives on the Serial 0/0/0 interface on R2.
▪ 5. R2 de-encapsulates the frame and looks for a route to the
destination. R2 has a static route to 192.168.2.0/24 out of the Serial
0/0/1 interface.
▪ 6. R2 encapsulates the packet in a new frame. Because the link to R3 is
a point-to-point link, R2 adds an "all 1s" address for the Layer 2
destination address.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Troubleshoot Static and Default Route Issues
Static Routes and Packet Forwarding (cont.)
▪ 7. The frame is forwarded out of the Serial 0/0/1 interface. The packet
arrives on the Serial 0/0/1 interface on R3.
▪ 8. R3 de-encapsulates the frame and looks for a route to the
destination. R3 has a connected route to 192.168.2.0/24 out of the
GigabitEthernet 0/0 interface.
▪ 9. R3 looks up the ARP table entry for 192.168.2.10 to find the Layer
2 MAC address for PC3. If no entry exists, R3 sends an ARP request
out of the GigabitEthernet 0/0 interface, and PC3 responds with an
ARP reply, which includes the PC3 MAC address.
▪ 10. R3 encapsulates the packet in a new frame with the MAC address
of the GigabitEthernet 0/0 interface as the source Layer 2 address
and the MAC address of PC3 as the destination MAC address.
▪ 11. The frame is forwarded out of GigabitEthernet 0/0 interface. The
packet arrives on the network interface card (NIC) interface of PC3.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Troubleshoot IPv4 Static and Default Route Configuration
Troubleshoot a Missing Route
Common IOS troubleshooting commands include:
▪ ping!
▪ traceroute!
▪ show ip route!
▪ show ip interface brief!
▪ show cdp neighbors detail
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Troubleshoot IPv4 Static and Default Route Configuration
Solve a Connectivity Problem
▪ Finding a missing (or misconfigured) route is a relatively
straightforward process, if the right tools are used in a methodical
manner.
▪ Use the ping command to confirm the destination can’t be reached.
▪ A traceroute would also reveal what is the closest router (or hop)
that fails to respond as expected. In this case, the router would then
send an Internet Control Message Protocol (ICMP) destination
unreachable message back to the source.
▪ The next step is to investigate the routing table. Look for missing or
misconfigured routes.
▪ Incorrect static routes are a common cause of routing problems.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 2: Summary
▪ Static routes can be configured with a next-hop IP
address, which is commonly the IP address of the nexthop router.
▪ When a next-hop IP address is used, the routing table
process must resolve this address to an exit interface.
▪ On point-to-point serial links, it is usually more efficient to
configure the static route with an exit interface.
▪ On multi-access networks, such as Ethernet, both a nexthop IP address and an exit interface can be configured on
the static route.
▪ Static routes have a default administrative distance of "1".
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 2: Summary (cont.)
▪ A static route is only entered in the routing table if the
next-hop IP address can be resolved through an exit
interface.
▪ Whether the static route is configured with a next-hop IP
address or exit interface, if the exit interface that is used to
forward that packet is not in the routing table, the static
route is not included in the routing table.
▪ In many cases, several static routes can be configured as
a single summary route.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Chapter 2: Summary (cont.)
▪ The ultimate summary route is a default route, configured
with a 0.0.0.0 network address and a 0.0.0.0 subnet mask.
▪ If there is not a more specific match in the routing table,
the routing table uses the default route to forward the
packet to another router.
▪ A floating static route can be configured to back up a main
link by manipulating its administrative value.
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›
Presentation_ID
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
‹#›