Icnd210 s04l01

© 2007 Cisco Systems, Inc. All rights reserved. ICND2 v1.0—4-1
Single-Area OSPF Implementation
Implementing
OSPF

OSPF Overview
 Creates a neighbor relationship by exchanging hello packets
 Propagates LSAs rather than routing table updates
– Link: Router interface
– State: Description of an interface and its relationship to
neighboring routers
 Floods LSAs to all OSPF routers in the area, not just directly
connected routers
 Pieces together all the LSAs generated by the OSPF routers to
create the OSPF link-state database
 Uses the SPF algorithm to calculate the shortest path to each
destination and places it in the routing table

OSPF Hierarchy Example
 Minimizes routing table entries
 Localizes the impact of a topology change within an area

Neighbor Adjacencies: The Hello Packet

SPF Algorithm
 Places each router at the root of a tree and calculates the
shortest path to each destination based on the cumulative cost
 Cost = Reference Bandwidth / Interface Bandwidth (b/s)
10
1
10
1
1

Configuring Single-Area OSPF
network address wildcard-mask area area-id
 Assigns networks to a specific OSPF area
router ospf process-id
 Defines OSPF as the IP routing protocol
RouterX(config)#
RouterX(config-router)#

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
 Can be set manually using the router-id command

Verifying the OSPF Configuration
RouterX# show ip protocols
 Verifies that OSPF is configured
RouterX# show ip route
 Displays all the routes learned by the router
RouterX# show ip route
Codes: I - IGRP derived, R - RIP derived, O - OSPF derived,
C - connected, S - static, E - EGP derived, B - BGP derived,
E2 - OSPF external type 2 route, N1 - OSPF NSSA external type 1 route,
N2 - OSPF NSSA external type 2 route
Gateway of last resort is 10.119.254.240 to network 10.140.0.0
O 10.110.0.0 [110/5] via 10.119.254.6, 0:01:00, Ethernet2
O IA 10.67.10.0 [110/10] via 10.119.254.244, 0:02:22, Ethernet2
O 10.68.132.0 [110/5] via 10.119.254.6, 0:00:59, Ethernet2
O 10.130.0.0 [110/5] via 10.119.254.6, 0:00:59, Ethernet2
O E2 10.128.0.0 [170/10] via 10.119.254.244, 0:02:22, Ethernet2
. . .

Verifying the OSPF Configuration (Cont.)
RouterX# show ip ospf
Routing Process "ospf 50" with ID 10.64.0.2
<output omitted>
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Number of areas transit capable is 0
External flood list length 0
Area BACKBONE(0)
Area BACKBONE(0)
Area has no authentication
SPF algorithm last executed 00:01:25.028 ago
SPF algorithm executed 7 times
<output omitted>
 Displays the OSPF router ID, timers, and statistics
RouterX# show ip ospf

RouterX# show ip ospf interface ethernet 0
Ethernet 0 is up, line protocol is up
Internet Address 192.168.254.202, Mask 255.255.255.0, Area 0.0.0.0
AS 201, Router ID 192.168.99.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State OTHER, Priority 1
Designated Router id 192.168.254.10, Interface address 192.168.254.10
Backup Designated router id 192.168.254.28, Interface addr 192.168.254.28
Timer intervals configured, Hello 10, Dead 60, Wait 40, Retransmit 5
Hello due in 0:00:05
Neighbor Count is 8, Adjacent neighbor count is 2
Adjacent with neighbor 192.168.254.28 (Backup Designated Router)
Adjacent with neighbor 192.168.254.10 (Designated Router)
RouterX# show ip ospf interface
 Displays the area ID and adjacency information

RouterX# show ip ospf neighbor
ID Pri State Dead Time Address Interface
10.199.199.137 1 FULL/DR 0:00:31 192.168.80.37 FastEthernet0/0
172.16.48.1 1 FULL/DROTHER 0:00:33 172.16.48.1 FastEthernet0/1
172.16.48.200 1 FULL/DROTHER 0:00:33 172.16.48.200 FastEthernet0/1
10.199.199.137 5 FULL/DR 0:00:33 172.16.48.189 FastEthernet0/1
RouterX# show ip ospf neighbor
 Displays the OSPF neighbor information on a per-interface basis

RouterX# show ip ospf neighbor 10.199.199.137
Neighbor 10.199.199.137, interface address 192.168.80.37
In the area 0.0.0.0 via interface Ethernet0
Neighbor priority is 1, State is FULL
Options 2
Dead timer due in 0:00:32
Link State retransmission due in 0:00:04
Neighbor 10.199.199.137, interface address 172.16.48.189
In the area 0.0.0.0 via interface Fddi0
Neighbor priority is 5, State is FULL
Options 2
Dead timer due in 0:00:32
Link State retransmission due in 0:00:03

RouterX# 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
OSPF: rcv. v:2 t:1 l:48 rid:200.0.0.117
aid:0.0.0.0 chk:6AB2 aut:0 auk:
RouterX# 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
OSPF debug Commands

Load Balancing with OSPF
OSPF load balancing:
 Paths must be equal cost
 By default, up to four equal-cost paths can be placed into the
routing table
 With a configuration change, up to a maximum of 16 paths can be
configured:
– (config-router)# maximum-paths <value>
 To ensure paths are equal cost for load balancing, you can
change the cost of a particular link:
– (config-if)# ip ospf cost <value>

Load Balancing with OSPF

OSPF Authentication
 OSPF supports two types of authentication:
– Plaintext (or simple) password authentication
– MD5 authentication
 The router generates and checks every OSPF packet.
 The router authenticates the source of each routing update
packet that it receives.
 Configure a “key” (password); each participating neighbor
must have the same key configured.

Configuring OSPF Plaintext Password
Authentication
ip ospf authentication-key password
RouterX(config-if)#
 Assigns a password to use with neighboring routers
RouterX(config-if)#
ip ospf authentication [message-digest | null]
 Specifies the authentication type for an interface (as of Cisco
IOS Release 12.0)
RouterX(config-router)#
area area-id authentication [message-digest]
 Specifies the authentication type for an area
OR

Plaintext Password Authentication
Configuration Example

Verifying Plaintext Password
Authentication
RouterX#show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.2.2.2 0 FULL/ - 00:00:32 192.168.1.102 Serial0/0/1
RouterX#show ip route
<output omitted>
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O 10.2.2.2/32 [110/782] via 192.168.1.102, 00:01:17, Serial0/0/1
C 10.1.1.0/24 is directly connected, Loopback0
192.168.1.0/27 is subnetted, 1 subnets
C 192.168.1.96 is directly connected, Serial0/0/1
RouterX#ping 10.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 28/29/32 ms

Visual Objective 4-1: Implementing OSPF

Summary
 OSPF is a classless, link-state routing protocol that uses an area hierarchy
for fast convergence.
 OSPF exchanges hello packets to establish neighbor adjacencies between
routers.
 The SPF algorithm uses a cost metric to determine the best path. Lower
costs indicate a better path.
 The router ospf process-id command is used to enable OSPF on the router.
 Use a loopback interface to keep the OSPF router ID consistent.
 The show ip ospf neighbor command displays OSPF neighbor information
on a per-interface basis.
 The commands debug ip ospf events and debug ip ospf packets can be
used to troubleshoot OSPF problems.
 OSPF will load-balance across up to four equal-cost metric paths by default.
 There are two types of OSPF authentication: Plaintext and MD5.

Icnd210 s04l01

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