Lab Exercise: Configuring OSPF Authentication This
lab is to setup an IP addressing scheme for Open Shortest Path
First (OSPF) area. Lab Activity e-Lab Activity:
Configuring OSPF Authentication In this lab, the student will
setup an IP addressing scheme for OSPF area, configure and
verify OSPF routing, and introduce OSPF authentication in to
the area. Web Links area authentication
http://www.cisco.com/en/US/products/sw/
iosswrel/ps1835/products_command_
reference_chapter09186a00800917e6.
html#1017391
Content 2.3 Single Area OSPF Configuration
2.3.5 Configuring OSPF timers OSPF routers must have the
same hello intervals and the same dead intervals to exchange
information. By default, the dead interval is four times the
value of the hello interval. This means that a router has four
chances to send a hello packet before being declared dead. On
broadcast OSPF networks, the default hello interval is 10
seconds and the default dead interval is 40 seconds. On
nonbroadcast networks, the default hello interval is 30 seconds
and the default dead interval is 120 seconds. These default
values result in efficient OSPF operation and seldom need to be
modified. A network administrator is allowed to choose these
timer values. A justification that OSPF network performance
will be improved is needed prior to changing the timers. These
timers must be configured to match those of any neighboring
router. To configure the hello and dead intervals on an
interface, use the following commands: Router(config-if)#ip
ospf hello-interval seconds
Router(config-if)#ip ospf dead-interval seconds
Lab Activity Lab Exercise: Configuring OSPF Timers This
lab is to setup OSPF timers. Lab Activity e-Lab
Activity: Configuring OSPF Timers In this lab, the student will
adjust OSPF timers to maximize efficiency of the network.
Web Links timers OSPF http://www.cisco.com/en/US/products/sw/
iosswrel/ps1835/products_command_
reference_chapter09186a00800917e6.
html#1020269
Content 2.3 Single Area OSPF Configuration
2.3.6 OSPF, propagating a default route OSPF routing
ensures loop-free paths to every network in the domain. To
reach networks outside the domain, either OSPF must know about
the network or OSPF must have a default route. To have an entry
for every network in the world would require enormous resources
for each router. A practical alternative is to add a default
route to the OSPF router connected to the outside network. This
route can be redistributed to each router in the AS through
normal OSPF updates. A configured default route is used by a
router to generate a gateway of last resort. The static default
route configuration syntax uses the network 0.0.0.0 address and
a subnet mask 0.0.0.0: Router(config)#ip route 0.0.0.0
0.0.0.0 [interface | next-hop address] This
is referred to as the quad-zero route, and any network address
is matched using the following rule. The network gateway is
determined by ANDing the packet destination with the subnet
mask. The following configuration statement will propagate this
route to all the routers in a normal OSPF area:
Router(config-router)#
default-information
originate All routers in the OSPF area will learn a default
route provided that the interface of the border router to the
default gateway is active. Lab Activity Lab Exercise:
Propagating Default Routes in an OSPF Domain This lab is to
setup an IP addressing scheme for OSPF area. Lab
Activity e-Lab Activity: Propagate Default Route
Information in an OSPF Domain In this lab, the student will
configure the OSPF network so that all hosts in the OSPF area
can connect to outside networks. Web Links
default-information originate (OSPF)
http://www.cisco.com/en/US/products/sw/
iosswrel/ps1835/products_command_
reference_chapter09186a00800917e6.
html#1025099
Content 2.3 Single Area OSPF Configuration
2.3.7 Common OSPF configuration issues An OSPF router must
establish a neighbor or adjacency relationship with another
OSPF router to exchange routing information. Failure to
establish a neighbor relationship is caused by any of the
following reasons: - Hellos are not sent from both
neighbors.
- Hello and dead interval timers are not the
same.
- Interfaces are on different network
types.
- Authentication passwords or keys are
different.
In OSPF routing it is also important to
ensure the following: - All interfaces have the correct
addresses and subnet mask.
- network area
statements have the correct wildcard masks.
-
network area statements put interfaces into the correct
area.
Web Links Troubleshooting OSPF
http://www.cisco.com/en/US/ tech/tk826/ tk365/technologies_
tech_ note09186a00800949f7.shtml
Content
2.3 Single Area OSPF Configuration 2.3.8
Verifying the OSPF configuration To verify the OSPF
configuration a number of show commands are available. Figure
lists these commands. Figure shows commands useful for
troubleshooting OSPF. Web Links Enabling Debug
Operations http://www.cisco.com/en/US/products/sw/
iosswrel/ps1835/products_configuration_
guide_chapter09186a00800ca74c.html
#1001661
Content
Summary An understanding of the following key points
should have been achieved: - The features of link-state
routing
- How link-state routing information is
maintained
- The link-state routing algorithm
- The advantages and disadvantages of link-state
routing
- Link-state routing compared with distance
vector routing
- OSPF terminology
- The
differences between distance vector and link-state routing
protocols
- OSPF network types
- The operation of
the shortest path first (SPF) algorithm
- The OSPF Hello
protocol
- The basics steps in the operation of
OSPF
- Enabling OSPF on a router
- Configuring a
loopback address to set router priority
- Changing OSPF
route preference by modifying the cost metric
- Configuring OSPF authentication
- Changing OSPF
timers
- Creating and propagating a default route
- Using show commands to verify OSPF operation