ICND20S05L07
Enabling OSPF
Objectives
Upon completing this lesson, you will be able to:
?Describe the features and operation of OSPF ?Use Cisco IOS commands to configure dynamic routing for a single area OSPF network, given a functioning router
?Use show and debug commands to identify
anomalies in dynamic routing operation using OSPF, given an operational router
Introducing OSPF
?Open standard
?Shortest path first (SPF) algorithm
?Link-state routing protocol (vs. distance vector)
OSPF as a Link-State Protocol
?OSPF propagates link-state advertisements
rather than routing table updates.
?LSAs are flooded to all OSPF routers in the area.?The OSPF link-state database is pieced together from the LSAs generated by the OSPF routers. ?OSPF uses the SPF algorithm to calculate the
shortest path to a destination.
–Link = router interface
–State = description of an interface and its
relationship to neighboring routers
OSPF Hierarchical Routing
?Consists of areas and autonomous systems ?Minimizes routing update traffic
Shortest Path First Algorithm
?Places each router at the root of a tree and calculates the
shortest path to each destination based on the cumulative cost ?Cost = 108/bandwidth (bps)
Configuring Single Area OSPF
Router(config)#router ospf process-id
?Defines OSPF as the IP routing protocol
Router(config-router)#network address mask area area-id ?Assigns networks to a specific OSPF area
OSPF Configuration Example
Configuring Loopback Interfaces
Router ID:
?Number by which the router is known to OSPF
?Default: The highest IP address on an active interface at the
moment of OSPF process startup
?Can be overridden by a loopback interface: Highest IP address of any active loopback interface
Verifying the OSPF Configuration
Router#show ip protocols
?Verifies that OSPF is configured
Router#show ip route
?Displays all the routes learned by the router
Router#show ip ospf interface
?Displays area-ID and adjacency information
Router#show ip ospf neighbor
?Displays OSPF-neighbor information on a per-interface basis
OSPF debug commands
Router#debug ip ospf events
OSPF:hello with invalid timers on interface Ethernet0 hello interval received 10 configured 10
net mask received 255.255.255.0 configured 255.255.255.0 dead interval received 40 configured 30
Router# debug ip ospf packet
OSPF: rcv. v:2 t:1 l:48 rid:200.0.0.117
aid:0.0.0.0 chk:6AB2 aut:0 auk:
Router#debug ip ospf packet
OSPF: rcv. v:2 t:1 l:48 rid:200.0.0.116
aid:0.0.0.0 chk:0 aut:2 keyid:1 seq:0x0
Summary
?OSPF is an interior gateway protocol similar to IGRP, but based on link states rather than
distance vectors.
?OSPF advertises information about each of its
links rather than sending routing table updates like a distance vector protocol.
?The SPF algorithm places each router at the root of a tree and calculates the shortest path to each destination based on the cumulative cost
required to reach that destination.
Summary (Cont.)
?Use the router ospf command to start an OSPF routing process and the network command to
associate addresses to an OSPF area.
?You can use any one of a number of show
commands to display information about an
OSPF configuration.
?To display information on OSPF-related events, such as adjacencies, flooding information,
designated router selection, and SPF
calculation, use the debug ip ospf events
privileged EXEC command.