Packet Tracer 4.0 Concept Building Activity: Using Floating Static Routes for a Backup Link

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Oct 28, 2013 (4 years and 13 days ago)

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5

Packet Tracer 4.0 Activity


Copyright


2006, Cisco Systems, Inc.




Packet Tracer 4.0 Concept Building Activity: Using Floating Static Routes for a
Backup Link


Objective

To configure floating static routes activate a backup link from a remote location when the primary link
fails.

Scenario

The topology in this lab sim
ulates an enterprise network for a company with the
headquarters in a location represented by Router0 and a branch office in a location
represented by Router1. Each location has a Fast Ethernet LAN represented by the
appropriate host attached to the FastEt
hernet port on each router. A leased T1 line operating
at 1.544 megabits per second serves as the primary connection between Router0 and
Router1. This link provides full connectivity between both sites and should be used to
forward all packets. In the even
t that the primary link goes down, the company has leased an
additional line between Router0 and Router1 to serve as a backup link. To lower the costs
associated with a leased line across the distance between Router0 and Router1, the second
link is a fract
ional T1 line operating at 56 kilobits per second. The company currently has
only these two locations but may add Internet access through Router0 and may open an
additional location that will also connect through Router0. To keep things simple and secure
o
n this small network, we will use static routing. Router1 is a stub network because it is a
branch location that connects only to Router0. Define a static route from Router0 to
Router1 LAN. Since we may provide Internet access through Router0 and Router1
will need
to reach Router0 and beyond we will define a default static route to Router0 on Router1 to
reach any host, including the Internet.

Required Files

To complete this lab, you will need the following files.



FloatingStaticRoutes.pka


Note: there are 2 serial links.

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5

Packet Tracer 4.0 Activity


Copyright


2006, Cisco Systems, Inc.


Plan:

Familiariz
e yourself with PT 4.0 help menu, in case you have questions. Open
FloatingStaticRoutes.pka and follow the Instructions, which are repeated below:


Act:

Step 1

Examine the configuration on both routers by issuing the
show running
-
config

from the CLI.
Issu
e the command
show ip interface brief

on both routers. Verify the all interfaces are up
and their line protocols are up. Troubleshoot as necessary.

Step 2

Ping from the command prompt on each host to the other host. The pings should fail. On each router
t
ype the command
show ip route

and examine the contents. The outputs are shown below:


Router0#
show ip route

Codes: C
-

connected, S
-

static, I
-

IGRP, R
-

RIP, M
-

mobile, B
-

BGP


D
-

EIGRP, EX
-

EIGRP external, O
-

OSPF, IA
-

OSPF inter area



N1
-

OSPF NSSA external type 1, N2
-

OSPF NSSA external type 2


E1
-

OSPF external type 1, E2
-

OSPF external type 2, E
-

EGP


i
-

IS
-
IS, L1
-

IS
-
IS level
-
1, L2
-

IS
-
IS level
-
2, ia
-

IS
-
IS inter area


*
-

candidate default, U
-

per
-
user

static route, o
-

ODR


P
-

periodic downloaded static route


Gateway of last resort is not set


C 192.168.14.0/24 is directly connected, FastEthernet0/0

C 192.168.15.0/24 is directly connected, Serial0/0

C 192.168.17.0/24 is directly connec
ted, Serial0/1


Router1#
show ip route

Codes: C
-

connected, S
-

static, I
-

IGRP, R
-

RIP, M
-

mobile, B
-

BGP


D
-

EIGRP, EX
-

EIGRP external, O
-

OSPF, IA
-

OSPF inter area


N1
-

OSPF NSSA external type 1, N2
-

OSPF NSSA external type 2



E1
-

OSPF external type 1, E2
-

OSPF external type 2, E
-

EGP


i
-

IS
-
IS, L1
-

IS
-
IS level
-
1, L2
-

IS
-
IS level
-
2, ia
-

IS
-
IS inter area


*
-

candidate default, U
-

per
-
user static route, o
-

ODR


P
-

periodic downloaded static route


Ga
teway of last resort is not set


C 192.168.15.0/24 is directly connected, Serial0/0

C 192.168.16.0/24 is directly connected, FastEthernet0/0

C 192.168.17.0/24 is directly connected, Serial0/1


The pings failed because neither router has a route to

the other routers LAN. The routing tables
contain only routes to directly connected networks.

Step 3

Configure a static route on Router0 using the primary T1 link from global configuration mode using
the following command:


Router0(config)#
ip route 192.1
68.16.0 255.255.255.0 192.168.15.2


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Packet Tracer 4.0 Activity


Copyright


2006, Cisco Systems, Inc.


Configure a static default route on Router1 using the primary T1 link from global configuration mode
using the following command:


Router1(config
)#ip route 0.0.0.0 0.0.0.0 192.168.15.1


Confirm your configuration by ping
ing from the command prompt on each host to the other host. All
pings should succeed. If not, troubleshoot as necessary.

Step 4

On each router type the command
show ip route

and examine the contents. The output from
both routers follows:


Router0#
show ip r
oute

Codes: C
-

connected, S
-

static, I
-

IGRP, R
-

RIP, M
-

mobile, B
-

BGP


D
-

EIGRP, EX
-

EIGRP external, O
-

OSPF, IA
-

OSPF inter area


N1
-

OSPF NSSA external type 1, N2
-

OSPF NSSA external type 2


E1
-

OSPF external type 1, E2
-

OSPF external type 2, E
-

EGP


i
-

IS
-
IS, L1
-

IS
-
IS level
-
1, L2
-

IS
-
IS level
-
2, ia
-

IS
-
IS inter area


*
-

candidate default, U
-

per
-
user static route, o
-

ODR


P
-

periodic downloaded static route


Gateway of last resort is not set


C 192.168.14.0/24 is directly connected, FastEthernet0/0

C 192.168.15.0/24 is directly connected, Serial0/0

S 192.168.16.0/24 [1/0] via 192.168.15.2

C 192.168.17.0/24 is directly connected, Serial0/1


Router1#
show ip route

Codes: C
-

connected,

S
-

static, I
-

IGRP, R
-

RIP, M
-

mobile, B
-

BGP


D
-

EIGRP, EX
-

EIGRP external, O
-

OSPF, IA
-

OSPF inter area


N1
-

OSPF NSSA external type 1, N2
-

OSPF NSSA external type 2


E1
-

OSPF external type 1, E2
-

OSPF external type 2, E
-

EGP


i
-

IS
-
IS, L1
-

IS
-
IS level
-
1, L2
-

IS
-
IS level
-
2, ia
-

IS
-
IS inter area


*
-

candidate default, U
-

per
-
user static route, o
-

ODR


P
-

periodic downloaded static route


Gateway of last resort is 192.168.15.1 to network 0.0.0.0


C

192.168.15.0/24 is directly connected, Serial0/0

C 192.168.16.0/24 is directly connected, FastEthernet0/0

C 192.168.17.0/24 is directly connected, Serial0/1

S* 0.0.0.0/0 [1/0] via 192.168.15.1


The outputs show the static route to the Router1 LA
N on Router0 and the static default route on
Router1.


1.

The static routes contain [1/0]. What does the 1 represent?

The 1 represents the default administrative distance for a static route.

2.

The static routes contain [1/0]. What does the 0 represent?

The 0
represents the metric, which is always 0 for a static route.

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Packet Tracer 4.0 Activity


Copyright


2006, Cisco Systems, Inc.


3.

If a packet arrives from PC0 (IP 192.168.14.2) on FastEthernet0/0 of Router0 intended for PC1
(IP 192.168.16.2). Out which interface will it be sent?

Serial0/0


The destination network matches
the static route that shows the next hop to be
192.168.15.2. The router does a recursive lookup for that destination network and finds the
outbound interface on the connected route above the static route.

Step 5

Shutdown the Serial0/0 interface on Router1

to bring down the T1 link. Enter
show ip route

on
both routers to observe the updated routing table. Notice that both static routes have disappeared
from the routing tables and neither router can reach the other’s LAN. Re
-
enable the Serial0/0
interface on

Router1

Step 6

We have a backup link available but it will not be used unless it is added to the routing table on both
routers. If we add these routes as we did for the primary routes they will be installed in the routing
table and traffic will also use
the backup link even if the primary route is available. We want these
routes to be available only when the primary link is down. The solution is floating static routes. These
routes are configured with an administrative distance greater than that of the pr
imary routes. If more
than one route is available to the same destination network the route is selected based on the
trustworthiness of the routing source. This trustworthiness is expressed as administrative distance.
The lower the administrative distance
the more trusted the source (the range of values is from 0,
directly connected, to 255, untrusted). Since static routes represent the administrator’s knowledge
they have a very low administrative distance of 1. To make our backup routes less attractive we
will
assign them an administrative distance of 5.


Enter the following commands in global configuration mode on both routers:


Router0(config)#
ip route 192.168.16.0 255.255.255.0 192.168.17.2 5


Router1(config)#
ip route 0.0.0.0 0.0.0.0 192.168.17.1 5


The
5 at the end of each represent the administrative distance. On both routers enter
show ip
route
. Notice that because of their higher administrative distance the backup routes are not added
to the routing tables.

Step 7

Shutdown the Serial0/0 interface on
Router1 to bring down the T1 link. Enter
show ip route

on
both routers to observe the updated routing table. The output for both routers is shown below:


Router0#
show ip route

Codes: C
-

connected, S
-

static, I
-

IGRP, R
-

RIP, M
-

mobile, B
-

BGP


D
-

EIGRP, EX
-

EIGRP external, O
-

OSPF, IA
-

OSPF inter area


N1
-

OSPF NSSA external type 1, N2
-

OSPF NSSA external type 2


E1
-

OSPF external type 1, E2
-

OSPF external type 2, E
-

EGP


i
-

IS
-
IS, L1
-

IS
-
IS level
-
1, L2
-

IS
-
IS level
-
2, ia
-

IS
-
IS inter area


*
-

candidate default, U
-

per
-
user static route, o
-

ODR


P
-

periodic downloaded static route


Gateway of last resort is not set


C 192.168.14.0/24 is directly connected, FastEthernet0/0

S 192.168.16.0/24 [5/0
] via 192.168.17.2

C 192.168.17.0/24 is directly connected, Serial0/1


Router1#
show ip route

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Packet Tracer 4.0 Activity


Copyright


2006, Cisco Systems, Inc.


Codes: C
-

connected, S
-

static, I
-

IGRP, R
-

RIP, M
-

mobile, B
-

BGP


D
-

EIGRP, EX
-

EIGRP external, O
-

OSPF, IA
-

OSPF inter area


N1
-

OSPF
NSSA external type 1, N2
-

OSPF NSSA external type 2


E1
-

OSPF external type 1, E2
-

OSPF external type 2, E
-

EGP


i
-

IS
-
IS, L1
-

IS
-
IS level
-
1, L2
-

IS
-
IS level
-
2, ia
-

IS
-
IS inter area


*
-

candidate default, U
-

per
-
user static rout
e, o
-

ODR


P
-

periodic downloaded static route


Gateway of last resort is 192.168.17.1 to network 0.0.0.0


C 192.168.16.0/24 is directly connected, FastEthernet0/0

C 192.168.17.0/24 is directly connected, Serial0/1

S* 0.0.0.0/0 [5/0] via 19
2.168.17.1


Notice that the backup routes have been installed in routing table. Confirm your configuration by
pinging from the command prompt on each host to the other host. All pings should succeed. If not,
troubleshoot as necessary.

Step 8

Re
-
enable the

Serial0/0 interface on Router1. Enter
show ip route

on both routers to observe the
updated routing table. Notice when the link is restored the primary routes are reinstalled in the
routing tables.

Step 9

Check your results by clicking the Check Results bu
tton. Correct any mistakes.