Transcript Static Routing - Home

Static Routing
Routing Protocols and Concepts – Chapter 2
Modified by Tony Chen
10/28/2008
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Notes:

If you see any mistake on my PowerPoint slides or if
you have any questions about the materials, please
feel free to email me at [email protected].
Thanks!
Tony Chen
College of DuPage
Cisco Networking Academy
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Objectives

Define the general role a router plays in networks.

Describe the directly connected networks, different
router interfaces

Examine directly connected networks in the routing
table and use the CDP protocol

Describe static routes with exit interfaces

Describe summary and default route

Examine how packets get forwarded when using
static routes

Identify how to manage and troubleshoot static routes
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General Role of the Router
 Functions of a Router
Best Path Selections
Forwarding packets to destination
 Routers perform packet forwarding by learning about
remote networks and maintaining routing information.
– The routers primary forwarding decision is based on Layer 3
information, the destination IP address.
– The router's routing table is used to find the best match
between the destination IP of a packet and a network address
in the routing table.
– The routing table will ultimately determine the exit interface to
forward the packet and the router will encapsulate that packet in
the appropriated data link frame for that outgoing interface.
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General Role of the Router
 Introducing the Topology
– The figure shows the topology used in this chapter.
– 3 1800 series routers connected via WAN links
– Each router connected to a LAN represented by a switch and a PC
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General Role of the Router
 Connections of a Router for WAN
-A router has a DB-60 port that can support 5
different cabling standards
–Newer routers support the smart serial
interface that allows for more data to be
forwarded across fewer cable pins.
 Connections of a Router for Ethernet
-2 types of connectors can be used: Straight
through and Cross-over
Straight through used to connect:
-Switch-to-Router, Switch-to-PC, Hub-toPC, Hub-to-Server
Cross-over used to connect (pin 1 connected
to pin 3, and pin 2 connected to pin 6):
-Switch-to-Switch, PC-to-PC, Switch-toHub, Hub-to-Hub, Router-to-Router, PCRouter
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General Role of the Router in COD
 Smart Serial cables: DCE and DTE
-Use straight cable to connect between
the DTE and DCE..
DCE and DTE Adapter
 Ethernet cables:
 Cross-over cable: RED cable
 Roll-over cable: flat cables
 Straight cable: all other cables
http://www.csdata.com/csdonline/customer/home.php
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Serial Connectors
DTE
DCE
DCE
DTE
DCE
DTE
 In our labs we will use serial DTE/DCE cables (no
CSU/DSU) with a DTE cable connected to one router and
a DCE cable connected to the other router.
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Interfaces
 Examining Router Interfaces
-Show IP router command – used to view routing table
-Show Interfaces command – used to show status of an interface
-Show IP Interface brief command – used to show a portion of
the interface information on a condensed format
-Show running-config command – used to show configuration
file in RAM
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Interfaces
 Configuring an Ethernet interface
-By default all serial and Ethernet interfaces are down
-To enable an interface use the No Shutdown command
•The show ip route
command is used to
display the routing table.
•Initially, the routing table is
empty if no interfaces have
been configured.
•Static routes and dynamic
routes will not be added to
the routing table until the
appropriate local interfaces
have been configured on
the router.
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Verifying Ethernet interface
- Show interfaces - command shows the status and gives a detailed
description for all interfaces on the router
– Show interfaces fastEthernet 0/0 – command used to show status of
fast Ethernet port
•R1#show interfaces fastethernet 0/0
•FastEthernet0/0 is administratively down, line protocol is down
• Administratively down means that the interface is currently in the shutdown mode, or turned off.
•Line protocol is down means, in this case, that the interface is not receiving a carrier signal from
a switch or the hub. This condition may also be due to the fact that the interface is in shutdown
mode
• You will notice that the show interfaces command does not show any IP addresses on R1's
interfaces. The reason for this is because we have not yet configured IP addresses on any of the
interfaces.
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Interfaces
 Verifying Ethernet interface
– Show run –
• command displays the current configuration file that
the router is using. Configuration commands are
temporarily stored in the running configuration file
and implemented immediately by the router.
•However, using show running-config is not
necessarily the best way to verify interface
configurations.
-Show ip interface brief –
-can be used to see a portion of the interface
information in a condensed format.
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Configuring an Ethernet interface
By default, all router interfaces are shutdown. To enable this
interface, use the no shutdown command, which changes the
interface from administratively down to up.
R1(config)#interface fastethernet 0/0
R1(config-if)#ip address 172.16.3.1 255.255.255.0
R1(config-if)#no shutdown
The following message is returned from the IOS:
*Mar 1 01:16:08.212: %LINK-3-UPDOWN: Interface
FastEthernet0/0, changed state to up
*Mar 1 01:16:09.214: %LINEPROTO-5-UPDOWN: Line
protocol on Interface FastEthernet0/0, changed state to up
–The first changed state to up message indicates that,
physically, the connection is good. If you do not get this first
message, be sure that the interface is properly connected to
a carrier signal from switch or a hub.
–The second changed state to up message indicates that the
Data Link layer is operational.
• However, WAN interfaces in a lab environment require
clocking on one side of the link. If you do not correctly set
the clock rate, then line protocol will not change to up.
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Configuring an Ethernet interface
 Unsolicited Messages from IOS
 The IOS often sends unsolicited messages.
 As you can see in the figure, sometimes these
messages will occur when you are in the middle
of typing a command, such as configuring a
description for the interface.
–The IOS message does not affect the command,
but it can cause you to lose your place when typing.
 In order to keep the unsolicited output separate
from your input, enter line configuration mode
for the consoled port and add the logging
synchronous command, as shown. You will see
that messages returned by IOS no longer
interfere with your typing.
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Interfaces
 Verifying Ethernet interface
-Show interfaces fastEthernet 0/0
 Reading the Routing Table
–Now look at routing table shown in the figure.
Notice R1 now has a "directly connected"
FastEthernet 0/0 interface a new network.
–The interface was configured with the
172.16.3.1/24 IP address which makes it a
member of the 172.16.3.0/24 network.
 172.16.0.0/24 is subnetted, 1 subnets
 C 172.16.3.0 is directly connected, FastEthernet0/0
–The C at the beginning of the route indicates
that this is a directly connected network. In other
words, R1 has an interface that belongs to this
network.
–The /24 subnet mask for this route is displayed
in the line above the actual route.
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Interfaces
 Reading the Routing Table
 172.16.0.0/24 is subnetted, 1 subnets
–Having a single route represent an entire
network of host IP addresses makes the
routing table smaller, with fewer routes,
which results in faster routing table
lookups.
•It means that this route matches all
packets with a destination address
belonging to this network.
–The routing table could contain all 254
individual host IP addresses for the
172.16.3.0/24 network, but that is an
inefficient way of storing addresses.
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Interfaces
 Verifying Ethernet interface
show interfaces fastethernet 0/0
show ip interface brief
 The show interfaces fastethernet 0/0 command
in the figure now shows
–The interface is up, and the line protocol is up.
The no shutdown command changed the
interface from administratively down to up.
–Notice that the IP address is now displayed.
 The command show ip interface brief in the
figure shows that the interface is up, and the
line protocol is up. (in a condensed format)
 Typically, the router's Ethernet or FastEthernet
interface will be the default gateway IP address
for any devices on that LAN.
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–For example, PC1 would be configured with a
IP address belonging to the 172.16.3.0/24
network, with the default gateway IP address
172.16.3.1.
–172.16.3.1 is router R1's FastEthernet IP
address.
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Ethernet Interfaces Participate in ARP
 A router's Ethernet interface participates
in a LAN network just like any other
device on that network.
–This means that these interfaces have a
Layer 2 MAC address, as shown in the figure.
The show interfaces command displays the
MAC address for the Ethernet interfaces.
–If a router has a packet destined for a
device on a directly connected Ethernet
network, it checks the ARP table for an entry
with that destination IP address in order to
map it to the MAC address.
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Interfaces
 Configuring a Serial interface
-Enter interface configuration mode
-Enter in the ip address and subnet mask
-Enter in the no shutdown command
 Example:
-R1(config)#interface serial 0/0/0
-R1(config-if)#ip address 172.16.2.1 255.255.255.0
-R1(config-if)#no shutdown
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Interfaces
 R1(config)#interface serial 0/0/0
 R1(config-if)#ip address 172.16.2.1 255.255.255.0
 R1(config-if)#no shutdown
 R2(config)#interface serial 0/0/0
 R2(config-if)#ip address 172.16.2.2 255.255.255.0
 R2(config-if)#no shutdown
–There is no requirement that both ends of the serial link use the same interface, (0/0/0, 0/0/1,
0/1/0, 0/1/1, ….)
–in this case, Serial 0/0/0. However, because both interfaces are members of the same
network, they both must have IP addresses that belong to the 172.16.2.0/24 network.
–If we now issue the show interfaces serial 0/0/0 command on either router, we still see that
the link is up/down.
 R2#show interfaces serial 0/0/0
 Serial0/0/0 is up, line protocol is down
– The physical link between R1 and R2 is up because both ends of the serial link have been
configured correctly with an IP address/mask and enabled with the no shutdown command.
– However, the line protocol is still down. This is because the interface is not receiving a clock
signal.
– There is still one more command that we need to enter, the clock rate command, on the
router with the DCE cable. The clock rate command will set the clock signal for the link.
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Interfaces
Step 1
Nothing is configured
Step 2
Setup IP but not “no shut”
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Step 3
Setup “no shut”
Step 4
Configured the clock rate
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 Examining Router Interfaces
-Physically connecting a WAN Interface.
-A WAN Physical Layer connection has sides:
Data Circuit-terminating Equipment (DCE) – This is the service
provider. CSU/DSU is a DCE device.
 The CSU/DSU (DCE device) is used to convert the data from the router (DTE
device) into a form acceptable to the WAN service provider.
a DCE device such as a CSU/DSU will provide the clock.
Data Terminal Equipment (DTE) – Typically the router is the DTE
device.
Up-to-date technology
Cisco 1-Port T1/Fractional T1
DSU/CSU WAN Interface Card
(WIC-1DSU-T1-V2=)
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- What is the significant of the information 1?
Interfaces
 For serial links that are directly interconnected, as in a
lab environment, one side of a connection must be
considered a DCE and provide a clocking signal.
 You can also distinguish DTE from DCE
–1) by looking at the connector between the two cables.
The DTE cable has a male connector, whereas the DCE
cable has a female connector.
–2) If a cable is connected between the two routers, you
can use the show controllers command to determine
which end of the cable is attached to that interface.
R1#show controllers serial 0/0/0
Interface Serial0/0/0
Hardware is PowerQUICC MPC860
DCE V.35, no clock
<output omitted>
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Interfaces
 Once the cable is attached, the clock can now be set with
the clock rate command.
–The available clock rates, in bits per second, are
1200, 2400, 9600, 19200, 38400, 56000, 64000,
72000, 125000, 148000, 500000, 800000,
1000000, 1300000, 2000000, and 4000000.
–Some bit rates might not be available on certain
serial interfaces.
 R1(config)#interface serial 0/0
 R1(config-if)#clock rate 64000
 01:10:28: %LINEPROTO-5-UPDOWN: Line protocol on
Interface Serial0/0, changed state to up
 Note: If a router's interface with a DTE cable is configured
with the clock rate command, the IOS will disregard the
command and there will be no ill effects.
–Use the “show controllers serial 0/0/0” to
find out whether it is a DTE or DCE cable.
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Testing
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Verifying the Serial Interface Configuration
R1#show interfaces
R1#show ip interface brief
R1#ping 172.16.2.2
R1#show ip route
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Routing Table Concepts
 The show ip route command reveals the content of the routing table.
–The main purpose of a routing table is to provide the router with paths to
different destination networks.
 The routing table consists of a list of "known" network addresses
–directly connected,
–configured statically,
–learned dynamically.
 POP Quiz:
– Can R1 ping R2?
– Can PC1 ping PC2?
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Routing Table Concepts
 Purpose of the debug ip routing command
Allows you to view changes that the router performs when adding or
removing routes in real time
3 disable interfaces with the shutdown command.
debugging with the debug ip routing command
1 enable
Configuring the IP address and Subnet Mask
4 Check the routing table
2
Check the routing table
5
Never use the debug all command on the production router.
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Disable debug ip
routing by using
either the “undebug
ip routing” command
or the “undebug all”
command.
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Routing Table and CDP Protocol
 When a router only has its interfaces configured &
no other routing protocols are configured then:
-The routing table contains only the directly connected
networks
-Only devices on the directly connected networks are
reachable
The output in this figure verifies that all
configured interfaces are "up" and "up".
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POP Quiz:
Why
pings
failed?
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Routing Table and CDP Protocol
 When a router only has its interfaces configured, and the
routing table contains the directly connected networks but
no other routes, only devices on those directly connected
networks are reachable.
–R1 can communicate with any device on the 172.16.3.0/24
and 172.16.2.0/24 networks.
–R2 can communicate with any device on the 172.16.1.0/24,
172.16.2.0/24, and 192.168.1.0/24 networks.
–R3 can communicate with any device on the 192.168.1.0/24
and 192.168.2.0/24 networks.
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Routing Table and CDP Protocol
 Checking each route in turn
–The ping command is used to
check end to end connectivity
–Ping 172.16.3.1 failed
•Route does not match any
route in the routing table
–Ping 192.168.1.1 succeed
•192.168.1.0/24, matches the
first 24 bits of the destination IP
address
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Routing Table and CDP Protocol
 Purpose of CDP
–Cisco Discovery Protocol (CDP) is a powerful
network monitoring and troubleshooting tool.
•CDP runs at the Data Link layer connecting the physical
media to the upper-layer protocols (ULPs).
•Because CDP operates at the Data Link layer, two or more
Cisco network devices, such as routers that support different
Network layer protocols (for example, IP and Novell IPX), can
learn about each other.
–A layer 2 cisco proprietary tool used to gather information
about other directly connected Cisco devices.
•enables you to access a summary of protocol and address
information about Cisco devices that are directly connected.
–the types of devices that are connected,
–the interfaces they are connected to,
–the interfaces used to make the connections,
–the model numbers of the devices.
–……..
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Routing Table and CDP Protocol
 Concept of neighbors
-2 types of neighbors
Layer 3 neighbors
 At Layer 3, routing protocols consider neighbors to be
devices that share the same network address space.
 R1 and R2 are neighbors. Both are members of the
172.16.1.0/24 network.
 R2 and R3 are also neighbors because they both share
the 192.168.1.0/24 network.
 But R1 and R3 are not neighbors because they do not
share any network address space.
Layer 2 neighbors
CDP operates at Layer 2 only. Therefore, CDP
neighbors are Cisco devices that are directly
connected physically and share the same data link.
»R1 and S1 are CDP neighbors.
»R1 and R2 are CDP neighbors.
»R2 and S2 are CDP neighbors.
»R2 and R3 are CDP neighbors.
»R3 and S3 are CDP neighbors.
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Notice the difference between Layer 2 and
Layer 3 neighbors. The switches are not
neighbors to the routers at Layer 3, because
the switches are operating at Layer 2 only.
However, the switches are Layer 2 neighbors
to their directly connected routers.
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Routing Table and CDP Protocol
 CDP is on by default.
–CDP exchanges hardware and software
device information with its directly connected
CDP neighbors.
 CDP show commands
Show cdp neighbors command
-Displays the following information:
Neighbor device ID
Local interface
Holdtime value, in seconds
Neighbor device capability code
Neighbor hardware platform
Neighbor remote port ID
Show cdp neighbors detail command
-It can also reveals the IP address of a
neighboring device
–knowing the IP address of the CDP neighbor is
often allows you to telnet into that device.
• and a lot more
– IOS version
– Platform
– …………
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Routing Table and CDP Protocol
 Disabling CDP
– CDP be a security risk
• Because some IOS versions send out CDP advertisements
by default, it is important to know how to disable CDP.
–If you need to disable CDP globally, for the entire device, use
this command:
• Router(config)#no cdp run
–If you want to use CDP but need to stop CDP advertisements
on a particular interface, use this command:
• Router(config-if)#no cdp enable
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Static Routes
 A router can learn about remote networks in one of two ways:
–Manually, from configured static routes
–Automatically, from a dynamic routing protocol
•Dynamic routing protocols are introduced in the next chapter.
 Purpose of a static route
–A manually configured route used when routing from a network to a stub
network
•A stub network is a network accessed by a single route.
•For an example, here we see that any
network attached to R1 would only have
one way to reach other destinations,
whether to networks attached to R2 or
to destinations beyond R2.
•Therefore, network 172.16.3.0 is a
stub network and R1 is a stub router.
•Running a routing protocol between R1
and R2 is a waste of resources
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Static Routes
 IP route command
To configure a static route use the following command: ip route
Example:
-Router(config)# ip route network-address subnet-mask {ipaddress | exit-interface }
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Static route operation Example: Fly from Chicago to LA
Chicago
O’Hare
Los
Angeles
Chicago  O’Hare Airport  Los Angeles
RTR(config)# ip route prefix mask {address | interface}
Los
Angeles
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Static Routes
 Remember R1 knows about its directly
connected networks.
–These are the routes currently in its
routing table.
 The remote networks that R1 does not
know about are:
–172.16.1.0/124 - The LAN on R2
–192.168.1.0/24 - The serial network
between R2 and R3
–192.168.2.0/24 - The LAN on R3
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Static Routes
R1(config)#ip route 172.16.1.0 255.255.255.0 172.16.2.2
 Dissecting static route syntax
ip route - Static route command
172.16.1.0 – Destination network address
255.255.255.0 - Subnet mask of destination
network
172.16.2.2 - Serial 0/0/0 interface IP address
on R2, which is the "next-hop" to this network
 show ip route output
–S - Routing table code for static route
–172.16.1.0 - Network address for the route
–/24 - Subnet mask for this route; this is
displayed in the line above, known as the parent
route, and discussed in Chapter 8
–[1/0] - Administrative distance and metric for
the static route (explained in a later chapter)
–via 172.16.2.2 - IP address of the next-hop
router, the IP address of R2's Serial 0/0/0
interface
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Static Routes
R1(config)#ip route 172.16.1.0 255.255.255.0 172.16.2.2
 show ip route output
–S - Routing table code for static route
–172.16.1.0 - Network address for the route
–/24 - Subnet mask for this route; this is
displayed in the line above, known as the parent
route, and discussed in Chapter 8
–[1/0] - Administrative distance and metric for
the static route (explained in a later chapter)
–via 172.16.2.2 - IP address of the next-hop
router, the IP address of R2's Serial 0/0/0
interface
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Static Routes
 Configuring routes to 2 or more remote networks
Use the following commands for R1
-R1(config)#ip route 192.168.1.0 255.255.255.0 172.16.2.2
-R1(config)#ip route 192.168.2.0 255.255.255.0 172.16.2.2
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Static Routes
 Zinin’s 3 routing principles
Principle 1: "Every router makes its decision alone, based on the information it has
in its own routing table.“
 R1 has three static routes in its routing table and makes forwarding decisions
based solely upon the information in the routing table.
 R1 does not consult the routing tables in any other routers.
 Making each router aware of remote networks is the responsibility of the
network administrator.
Principle 2: "The fact that one router has certain information in its routing table does
not mean that other routers have the same information.“
 The network administrator would be responsible for ensuring that the next-hop
router also has a route to this network
 Using Principle 2, we still need to configure the proper routing on the other
routers (R2 and R3) to make sure that they have routes to these three networks.
Principle 3: "Routing information about a path from one network to another does not
provide routing information about the reverse, or return path.“
 Most of the communication over networks is bidirectional. This means that
packets must travel in both directions between the end devices involved.
 Using Principle 3 as guidance, we will configure proper static routes on the other
routers to make sure they have routes back to the 172.16.3.0/24 network.
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Static Routes
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Static Routes with next-hop IP address
 Resolving to an Exit Interface
-Recursive route lookup - Occurs when the router has to perform multiple
lookups in the routing table before forwarding a packet. A static route that
forwards all packets to the next-hop IP address goes through the following
process (reclusive route lookup)
 (Step 1) The router first must match static route’s destination IP
address with the Next hop address
 The packet's destination IP address is matched to the static route
192.168.2.0/24 with the next-hop IP address 172.16.2.2.
 (Step 2) The next hop address is then matched to an exit interface
The next-hop IP address of the static route, 172.16.2.2, is matched to the
directly connected network 172.16.2.0/24 with the exit interface of Serial 0/0/0.
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Static Routes with Exit Interfaces
 Configuring a Static route with an Exit
Interface
-Static routes configured with an exit interface
are more efficient because the routing
–The routing table can resolve the exit interface
in a single search instead of 2 searches
 If the static route cannot be resolved to an
exit interface, the static route is removed from
the routing table
–Notice from the debug output that all three
static routes were deleted when the Serial 0/0/0
interface was shut down.
–They were deleted because all three static
routes were resolved to Serial 0/0/0.
–However, the static routes are still in the R1's
running configuration. If the interface comes
back up (is enabled again with no shutdown),
the IOS routing table process will reinstall these
static routes back into the routing table.
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Static Routes with Exit Interfaces
 Modifying Static routes
Existing static routes cannot be modified. The old static route
must be deleted by placing no in front of the ip route
Example:
-no ip route 192.168.2.0 255.255.255.0 172.16.2.2
A new static route must be rewritten in the configuration
R1(config)# no ip route 192.168.2.0 255.255.255.0 172.16.2.2
R1(config)#ip route 192.168.2.0 255.255.255.0 serial 0/0/0
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Static Routes with Exit Interfaces
 Verifying the Static Route Configuration
-Use the following commands
Step 1 show running-config
Step 2 verify static route has been entered correctly
Step 3 show ip route
Step 4 verify route was configured in routing table
Step 5 issue ping command to verify packets can
reach destination and that Return path is working
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Static route operation
Both types of the routes
all have distance of 1
and metric of 0.
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Static Routes with Exit Interfaces
 Ethernet interfaces and ARP.
– If a static route is configured on an Ethernet link
•If the packet is sent to the next-hop router then…
–the destination MAC address will be the address of the next
hop’s Ethernet interface
–This is found by the router consulting the ARP table.
»If an entry isn’t found then an ARP request will be sent out
R1(config)#ip route 192.168.2.0 255.255.255.0 fa 0/1
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Static Routes with Exit Interfaces
R1(config)#ip route 192.168.2.0 255.255.255.0 fastethernet 0/1
 Best not to use only an exit interface with Ethernet interfaces.
 Router will have difficulty determining the destination MAC address.
 With Ethernet networks, many different devices can be sharing the
same multiaccess network, including hosts and even multiple routers.
 Router will not have sufficient information to determine which device
is the next-hop device.
 Use both the next-hop interface and the exit interface for
Ethernet exit interfaces.
 Only a single route lookup now needed.
R1(config)#ip route 192.168.2.0 255.255.255.0 fastethernet 0/1 172.16.2.2
The routing table entry for this route would be:
S 192.168.2.0/24 [1/0] via 172.16.2.2 FastEthernet0/1
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Summary and Default Route
 Summarizing routes reduces the size of the routing
table.
 Route summarization is the process of combining a
number of static routes into a single static route.
–For example, the networks 10.0.0.0/16, 10.1.0.0/16,
10.2.0.0/16, 10.3.0.0/16, 10.4.0.0/16, 10.5.0.0/16, all the way
through 10.255.0.0/16 can be represented by a single network
address: 10.0.0.0/8.
 Multiple static routes can be summarized into a single
static route if:
–The destination networks can be summarized into a single
network address, and
–The multiple static routes all use the same exit-interface or
next-hop IP address
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Calculating a summary route

Here's the process of creating the summary route
172.16.1.0/22, as shown in the figure:
1. Write out the networks that you want to summarize in
binary.
2. To find the subnet mask for summarization, start with
the left-most bit.
3. Work your way to the right, finding all the bits that
match consecutively.
4. When you find a column of bits that do not match,
stop. You are at the summary boundary.
5. Now, count the number of left-most matching bits,
which in our example is 22. This number becomes
your subnet mask for the summarized route, /22 or
255.255.252.0
6. To find the network address for summarization, copy
the matching 22 bits and add all 0 bits to the end to
make 32 bits.

By following these steps, we can discover that the 3
static routes on R3 can be summarized into a single
static route, using the summary network address of
172.16.0.0 255.255.252.0:
ip route 172.16.0.0 255.255.252.0 Serial0/0/1
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Example: Calculating a summary route
 Which address can be used to
summarize networks 172.168.0.0 /24
through 172.168.7.0 /24?








10101100
10101100
10101100
10101100
10101100
10101100
10101100
10101100
10101000
10101000
10101000
10101000
10101000
10101000
10101000
10101000
00000000
00000001
00000010
00000011
00000100
00000101
00000110
00000111
00000000
00000000
00000000
00000000
00000000
00000000
00000000
00000000
 Answer:
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Example: Calculating a summary route
 Which address can be
used to summarize
networks
 11000000
•
•
•
•
•
•
•
•
192.1.1.0/27
192.1.1.32/27
192.1.1.64/28
192.1.1.80/28
192.1.1.96/29
192.1.1.104/29
192.1.1.112/29
192.1.1.120/29
00000001 00000001
 11000000 00000001 00000001
 11000000 00000001 00000001
 11000000 00000001 00000001
00000000
00100000
01000000
01010000




01100000
01101000
01110000
01111000
11000000
11000000
11000000
11000000
00000001 00000001
00000001 00000001
00000001 00000001
00000001 00000001
 Answer:
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Summary Route
 Configuring a summary route
–Step 1: Delete the current static route
R3(config)#no ip route 172.16.1.0 255.255.255.0 serial0/0/1
R3(config)#no ip route 172.16.2.0 255.255.255.0 serial0/0/1
R3(config)#no ip route 172.16.3.0 255.255.255.0 serial0/0/1
–Step 2: Configure the summary static route
•R3(config)#ip route 172.16.0.0 255.255.252.0 serial0/0/1
–Step 3: Verify the new static route
•show ip route
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ping
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Summary Route
 Static routes and subnet masks
–The routing table lookup process will use the most specific match
when comparing destination IP address and subnet mask
–For example, what if we had the following two static routes in the
routing table
•172.16.0.0/24 is subnetted, 3 subnets
•S 172.16.1.0 is directly connected, Serial0/0/0 and
•S 172.16.0.0/16 is directly connected, Serial0/0/1
–Consider a packet with the destination IP address 172.16.1.10. This
IP address matches both routes.
•The routing table lookup process will use the most-specific match.
•Because 24 bits match the 172.16.1.0/24 route, and only 16 bits of
the 172.16.0.0/16 route match, the static route with the 24 bit match
will be used.
•This is the longest match.
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Default Route
 Default Static Route
This is a route that will match all packets.
Like route summarization this will help reduce
the size of the routing table
 Default static routes are used:
–When no other routes in the routing table match the
packet's destination IP address. A common use is
when connecting a company's edge router to the ISP
network.
–When a router has only one other router to which it
is connected. This condition is known as a stub
router.
 Configuring a default static route
Similar to configuring a static route. Except
that destination IP address and subnet mask
are all zeros
Example:
-Router(config)#ip route 0.0.0.0 0.0.0.0
[exit-interface | ip-address ]
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Summary and Default Route
 R1 is a stub router.
–It is only connected to R2.
–Currently R1 has three static routes,
which are used to reach all of the remote
networks in our topology.
–All three static routes have the exit
interface Serial 0/0/0, forwarding packets
to the next-hop router R2.
 R1 is an ideal candidate to have all
of its static routes replaced by a
single default route.
–First, delete the three static routes
–Next, configure the single default static
route using the same Serial 0/0/0 exit
interface
R1(config)#ip route 0.0.0.0 0.0.0.0 serial 0/0/0
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Static Routes and Packet Forwarding
 Verify the change to the routing table
with the show ip route command
 S* 0.0.0.0/0 is directly connected, Serial0/0/0
–Note the * or asterisk next to the S.
•As you can see from the Codes table in
the figure, the asterisk indicates that this
static route is a candidate default route.
–The key to this configuration is the /0
mask.
•We previously said that it is the subnet
mask in the routing table that determines
how many bits must match between the
destination IP address of the packet and
the route in the routing table.
•A /0 mask indicates that zero or no bits
are needed to match.
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Self test: Static and static default route
 Can you use both static and
static default route to
configure the communication
between both LANS and the
communication to the
Internet.
-Only 3 statement of static route
needed to setup the network.
-1 static route
-2 default static route
WinterPark(config)# ip route 0.0.0.0 0.0.0.0 192.168.146.1
Altamonte(config)# ip route 10.0.234.0 255.255.255.0 192.168.146.2
Altamonte(config)# ip route 0.0.0.0 0.0.0.0 s0/1
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Static Routes and Packet Forwarding
 Troubleshooting a Missing Route
 Tools that can be used to isolate routing problems
include:
Layer 3
-Ping– tests end to end connectivity
-Traceroute– used to discover all of the hops (routers) along the
path between 2 points
-Show IP route– used to display routing table & ascertain
forwarding process
Layer 2
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-Show ip interface brief- used to show status of router interfaces
-Show cdp neighbors detail– used to gather configuration
information about directly connected neighbors
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Static Routes and Packet Forwarding
 Solving a Missing Route
 Finding a missing or mis-configured route requires
methodically using the correct tools
-Start with PING. If ping fails then use traceroute to determine
where packets are failing to arrive
- Than trace route
 Issue: show ip route to examine routing table.
-If there is a problem with a mis-configured static route remove
the static route then reconfigure the new static route
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Summary
 Routers
-Operate at layer 3
-Functions include best path selection & forwarding packets
 Connecting Networks
WANs
Serial cables are connected to router serial ports.
In the lab environment clock rates must be configured for DCE
LANs
Straight through cables or cross over cables are used to
connect to fastethernet port. (The type of cable used depends
on what devices are being connected)
 Cisco Discovery Protocol
A layer 2 proprietary protocol
Used to discover information about directly connected Cisco
devices
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Summary
 Static Routes
-This is a manually configured path that specifies how the router
will get to a certain point using a certain path.
 Summary static routes
-This is several static routes that have been condensed into a
single static route.
 Default route
-It is the route packets use if there is no other possible match for
their destination in the routing table.
 Forwarding of packets when static route is used
-Zinin’s 3 routing principles describe how packets are forwarded
 Troubleshooting static routes may require some of the following
commands:
-Ping
-Traceroute
-Show IP route
-Show ip interface brief
-Show cdp neighbors detail
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