1. Single-Area OSPF Implementation
Implementing OSPF
Single-Area OSPF Implementation

2. OSPF Overview Link – state AD = 110 Metric = cost (bandwidth)
Protocol = IP
Protocol_id = 89
Load balancing
Purpose: This figure presents the IGRP metric with its five possible components.
Emphasize : Bandwidth and delay are the two metrics that are most commonly used. They also comprise the default metric.
Note: Changing IGRP metrics can have great impact on network performance.
Describe the IGRP 24-bit metric field, as follows:
Bandwidth—Minimum bandwidth on the route, in kilobits per second.
Delay—Route delay, in tens of microseconds.
Reliability—Likelihood of successful packet transmission, expressed as an integer from 0 to 255.
Loading—Effective bandwidth of path.
MTU—Minimum MTU in path, expressed in bytes.
The following equation calculates the metric. It is presented for instructors and is not required to be taught:
metric = [k1 x bandwidth + (k2 x bandwidth) / (256 - load) + k3 x delay]
If k5 does not equal 0, an additional operation is done:
metric = metric x (k5/(reliability + k4))
The default constant values are k1 = k3 = 1 and k2 = k4 = k5 = 0.
Again, if default values are set, metric = bandwidth + delay.
The constants (k1, k2, k3) can be changed using the metric weights command. Changes to the IGRP constant values should be made with great care.

3. 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
Purpose: This figure presents the IGRP metric with its five possible components.
Emphasize : Bandwidth and delay are the two metrics that are most commonly used. They also comprise the default metric.
Note: Changing IGRP metrics can have great impact on network performance.
Describe the IGRP 24-bit metric field, as follows:
Bandwidth—Minimum bandwidth on the route, in kilobits per second.
Delay—Route delay, in tens of microseconds.
Reliability—Likelihood of successful packet transmission, expressed as an integer from 0 to 255.
Loading—Effective bandwidth of path.
MTU—Minimum MTU in path, expressed in bytes.
The following equation calculates the metric. It is presented for instructors and is not required to be taught:
metric = [k1 x bandwidth + (k2 x bandwidth) / (256 - load) + k3 x delay]
If k5 does not equal 0, an additional operation is done:
metric = metric x (k5/(reliability + k4))
The default constant values are k1 = k3 = 1 and k2 = k4 = k5 = 0.
Again, if default values are set, metric = bandwidth + delay.
The constants (k1, k2, k3) can be changed using the metric weights command. Changes to the IGRP constant values should be made with great care.

4. Link-State Routing Protocols
Purpose: This figure introduces the link-state routing algorithm, the second of the classes of routing protocols, and outlines how it operates.
Emphasize: In contrast with the analogy about the distance vector information being like individual road signs that show distance, link-state information is somewhat analogous to a road map with a “you are here” pointer showing the map reader’s current location. This larger perspective indicates the shortest path to the destination. Each router has its own map of the complete topology.
Link-state routing is not covered further in this course. Refer students interested in more details to the ACRC course.
After an initial flood of LSAs, link-state routers pass small, event-triggered link-state updates to all other routers.

5. Autonomous Systems: Interior and Exterior Routing Protocols
Purpose: This figure discusses autonomous systems, IGPs and EGPs.
Emphasize: Introduce the interior/exterior distinctions for routing protocols, as follows:
Interior routing protocols are used within a single autonomous system
Exterior routing protocols are used to communicate between autonomous systems
The design criteria for an interior routing protocol require it to find the best path through the network. In other words, the metric and how that metric is used is the most important element in an interior routing protocol.
Exterior protocols are used to exchange routing information between networks that do not share a common administration. IP exterior gateway protocols require the following three sets of information before routing can begin:
A list of neighbor (or peer) routers or access servers with which to exchange routing information
A list of networks to advertise as directly reachable
The autonomous system number of the local router
An autonomous system is a collection of networks within a common administrative domain.
Interior gateway protocols operate within an autonomous system.
Exterior gateway protocols connect different autonomous systems.

6. Benefits and Drawbacks of Link-State Routing
Benefits of link-state routing:
Fast convergence:
Changes are reported immediately by the affected source
Robustness against routing loops:
Routers know the topology
Link-state packets are sequenced and acknowledged
Hierarchical network design enables optimization of resources.
Drawbacks of link-state routing:
Significant demands for resources:
Memory (three tables: adjacency, topology, forwarding)
CPU (Dijkstra’s algorithm can be intensive, especially when there are many instabilities)
Requires very strict network design
Configuration can be complex when tuning various parameters and when design is complex

7. OSPF Operation
Select Router ID
Establish neighborly relations
LSDB (Link State Database) exchange.
Build the routing table

8. 1. Elected Router ID
router id:
router id:
Assume fa0/1 is down -> ?
The highest IP address of the interface is active.
The loopback port priority.

9. 2. Establish neighborly relations
- OSPF send hello packets to multicast addr ( )
Hello packets components:
Area – id.
Hello timer and Dead timer.
The IP address connected to the same subnet.
Meet the conditions of authentication.
On or off the flag stub.

10. Neighbor Adjacencies: The Hello Packet

11. Area – id.
Internal router: R2,R3,…
Router ABR – Area Border Router: R4,R5
Each area will have a valid identifier for the area called Area-id
Area 0 is called the Backbone Area.
All other area are required to have a serial connection to Area 0.

12. Hello timer and Dead timer.
Hello timer is the time to periodically send hello packets (default: 10s) -> reset Dead timer (40s)
The IP address connected to the same subnet
Meet the conditions of authentication

13. Flag stub Area
A stub area is an area that does not allow AS External (type 5) LSAs

14. 3. LSDB exchange.
The router will floods information unit called the LSA - Link State Advertisement to Elected Designated Router (DR router) and Backup Designated Router (BDR router)
Depends on network – type:
Point – to – point
Broadcast Multiaccess

15. Point – to – point links
Send all information on LSDB table Relation status from 2-way to FULL

16. Broadcast Multiaccess Links
Elected Designated Router (DR router) Elected Backup DR (BDR) Other router- DROther

17. Elected Designated Router (DR router)
Router priority (0-255)
Router priority default = 1.
Router priority highest – DR
Router priority smaller – BDR
Router priority = 0 – no elected.
Other priority - DROther
IF priority of Router X highest DR then. . . ?

18. Broadcast Multiaccess Links
DROther –> DROther : no (2-way relations) DROther –> DR, BDR: (FULL\ DR, BDR relations) DR -> Other routers: (FULL\ DR, BDR relations)

19. Build the routing table
After completion of the exchange LSDB, each router to get the database table link status of all routers in the area.
Based on this LSDB, the router used Dijkstra algorithm to build a shortest path first with metric as:
Metric = cost = 108/Bandwidth (bit per second).
Metric defaults:
Ethernet (BW = 10Mbps) -> cost = 10.
Fast Ethernet (BW = 100Mbps) -> cost = 1.
Serial (BW = 1.544Mbps – T1) -> cost = 64.

20. Sortest Path First Algorithm (SPF)10 10 1 1 1
Purpose: The figure presents how IGRP load sharing improves throughput and increases reliability.
Emphasize: Only feasible paths can be used for IGRP load sharing.
Load-balancing methods vary according to the switching mode because the data structures for process switching, fast switching, and autonomous switching are all different. When process switching, the processor load-balances packet by packet. When fast, autonomous, or silicon switching, load balancing is done destination by destination.
By default, the amount of variance is set to one, which results in equal-cost load balancing.
You can use the default-metric command to change the default metric.
Transition: The following pages describe how to configure the IGRP routing protocol.
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)

21. For example 1 Cost: R1 -> 192.168.3.0 = ?
Từ R1 đi đến mạng /24 của R3 sẽ đi qua các đường link Fast Ethernet có cost = 1
Serial có cost là 64 và link Fast Ethernet có cost bằng 1.
Vậy tổng cost tích lũy sẽ là là 66. Metric từ R1 đến mạng /24 là 66.

22. For example 2 Cost: 192.168.3.0 -> R1 = ?
Để tính tổng cost từ một mạng đích đến một router theo một đường (path) nào đó, ta thực hiện lần ngược từ đích lần về và cộng dồn cost theo quy tắc đi vào thì cộng, đi ra thì không cộng.

24. Configuring Single-Area OSPF
RouterX(config)#
router ospf process-id ( )
Defines OSPF as the IP routing protocol
RouterX(config-router)#
network address wildcard-mask area area-id
Assigns networks to a specific OSPF area
Slide 1 of 2
Purpose: This figure explains how to use the router igrp and network commands to configure an IGRP process.
Emphasize: Note that the AS keyword is required for IGRP.
You can use multiple network commands to specify all networks that are to participate in the IGRP process. Only those networks specified will be published to other routers.

25. 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

26. 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 to network
O [110/5] via , 0:01:00, Ethernet2
O IA [110/10] via , 0:02:22, Ethernet2
O [110/5] via , 0:00:59, Ethernet2
O [110/5] via , 0:00:59, Ethernet2
O E [170/10] via , 0:02:22, Ethernet2
. . .
240, 197, 102

27. Verifying the OSPF Configuration (Cont.)
RouterX# show ip ospf
Displays the OSPF router ID, timers, and statistics
RouterX# show ip ospf
Routing Process "ospf 50" with ID
<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 has no authentication
SPF algorithm last executed 00:01: ago
SPF algorithm executed 7 times

28. Verifying the OSPF Configuration (Cont.)
RouterX# show ip ospf interface
Displays the area ID and adjacency information
RouterX# show ip ospf interface ethernet 0
Ethernet 0 is up, line protocol is up
Internet Address , Mask , Area
AS 201, Router ID , Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State OTHER, Priority 1
Designated Router id , Interface address
Backup Designated router id , Interface addr
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 (Backup Designated Router)
  Adjacent with neighbor (Designated Router)

29. Verifying the OSPF Configuration (Cont.)
RouterX# show ip ospf neighbor
Displays the OSPF neighbor information on a per-interface basis
RouterX# show ip ospf neighbor
ID Pri State Dead Time Address Interface
  1 FULL/DR :00: FastEthernet0/0
FULL/DROTHER 0:00:   FastEthernet0/1
FULL/DROTHER 0:00:  FastEthernet0/1
  5 FULL/DR :00:  FastEthernet0/1

30. Verifying the OSPF Configuration (Cont.)
RouterX# show ip ospf neighbor
Neighbor , interface address
In the area 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 , interface address
In the area via interface Fddi0
Neighbor priority is 5, State is FULL
Link State retransmission due in 0:00:03

31. OSPF debug Commands RouterX# debug ip ospf events
OSPF:hello with invalid timers on interface Ethernet0
hello interval received 10 configured 10
net mask received configured
dead interval received 40 configured 30
OSPF: rcv. v:2 t:1 l:48 rid:
aid: chk:6AB2 aut:0 auk:
RouterX# debug ip ospf packet
OSPF: rcv. v:2 t:1 l:48 rid:
aid: chk:0 aut:2 keyid:1 seq:0x0

32. 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>

33. Load Balancing with OSPF

34. 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.

35. Configuring OSPF Plaintext Password Authentication
RouterX(config-if)#
ip ospf authentication-key password
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) OR
RouterX(config-router)#
area area-id authentication [message-digest]
Specifies the authentication type for an area

36. Plaintext Password Authentication Configuration Example

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

38. Visual Objective 4-1: Implementing OSPF
Lab 10 amended pod b and pod I addresses move core_ro address closer to interface same with s0 pod L
Objectives: Enable the IGRP dynamic routing protocol so your router can learn about nonconnected networks.
Purpose: Teach students how to enable IGRP.
Laboratory Instructions: Refer to the lab setup guide.

39. 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.