Dynamic Routing Protocol OSPF

Introduction to OSPF
By:
Atakan ATAK
Network Engineer
atakannatak@hotmail.com
July, 2017

Features of OSPF
Classless - Supporting VLSM and CIDR
Efficient – No need for periodic update
Secure - Authentication with MD5
Fast Convergence
Scalable
Link state or SPF technology
Uses its own 4th Layer protocols such
as protocol number 89
Dynamic Routing
OSPF routes have an administrative
distance is 110.
OSPF uses the Dijkstra Shortest Path
First algorithm to determine the
shortest path.
OSPF employs a hierarchical network
design using Areas.
OSPF uses cost as its metric, which is
computed based on the bandwidth of
the link. OSPF has no hop-count limit.

Components of OSPF
Database Table
Neighbor
Table
Topology
Table
Routing
Table
Neighbor
Database
Link State
Database
(LSDB)
• Keeps information about all other routers in
the network
• Represents network topology
• Same LSBD for all routers in the same area
• Show ip ospf database
Forwarding
Database
• List of all routers that a router
communicates bidirectionally
• Vary according to each routers
• Show ip ospf neighbors
• An algorithm, a route list created when the
link state is run in the database
• The routing table for each router is unique
• Show ip route
Information

OSPF in Multi Access Networks
Multiple access networks can create two problems
for OSPF in terms of the transfer of LSAs:
SW
Routers (n) Neighbors ( n(n-1)/2)
4 6
10 45
20 190
• Occurrence of multiple contiguities
• Lots of LSA transfers
Once the neighbors are established, link-state sharing
continues between the routers. The problem here,
each router communicates with the rest of all.
R2
R3
R4
R1

Multicast Addressing
OSPF uses IP multicast addressing to communicate
with routing peers. This reduces the overhead of
other devices on the same segment that are not
running OSPF.
When a OPSF update is sent on network, the
destination MAC address is modified to use the
reserved multicast range. 24 bits of the MAC address
are the lower 24 bits of the IP multicast address. With
OSPF, the relationship between the IP multicast
address and the MAC address is as follows:
• 224.0.0.5 – 01:00:5E:00:00:05 : All routers that speak
OSPF on the network
• 224.0.0.6 - 01:00:5E:00:00:06 : All DR/BDRon the
network
R1 (DR)
1.1.1.4
R3
1.1.1.1
R4
1.1.1.2
R2 (BDR)
1.1.1.3
R3 sends update
to all DRs using
IP address
224.0.0.6
R1 sends update
to all OSPF
router using IP
address
224.0.0.5

Calculate Path Cost Using SPF Algorithm
10.6.0.0/16
10.2.0.0/16
10.8.0.0/16
10.9.0.0/1610.4.0.0/16
10.11.0.0/16
10.7.0.0/16
10.3.0.0/16
10.10.0.0/16
10.5.0.0/16
10.1.0.0/16
20
10
2
2
5
2
5
20
10
10
20
R1
R3
R2
R4
R5
Target Path
R1->R2
R1->R2
10.5.0.0/16 R1->R2->R4
10.7.0.0/16 R1->R2->R3
10.8.0.0/16 R1->R2->R3
10.9.0.0./16 R1->R5
10.10.0.0/16 R1->R5
Cost
12
32
30
25
30
40
22
10.3.0.0/16
10.4.0.0/16
OSPF routers to obtain routing information and to achieve
merge status:
1. Setting up neighbors
2. Change of link status presentation with LSAs
3. Topology table creation
4. Executing the SPF Algorithm
The reason why you prefer the route to written blue in the
table below, SPF algorithm is choosing the shortest path.
Therefore, the other two routes are not preferred because
they cost more. Other paths:
1. R1->R2->R4 ---- Cost is 40
2. R1->R5->R4 ---- Cost is 50

Generic IPv4 Packet Header
Link header IP header
OSPF packet
types
Link trailer
Ethernet fields are shown
• Destination MAC Address
• Target MAC Address
IP Packets
• Destination IP Address
• Target IP Address
• Protocol ID is 89 Type Code
Router ID
Area ID
0x01 -- > Hello Packet
0x02 -- > Database Description (DBD)
0x03 -- > Link State Request (LSR)
0x04 -- > Link State Update (LSU)
0x05 -- > Link State Acknowledgment (LSAck)
Creation of neighborhs
Requesting a link from the router
Database synchronization
Reply to request
Confirm to LSU
LSA Type
1
2
3 or 4
5
6
7
Description
Router LSA
Summary LSA
Network LSA
Autonomous System External LSA
Multicast OSPF LSA
Defined for Not-So-Stubby-Areas
8
9-10-11
External attributes LSA for BGP
Opaque LSA

Type of LSAs
• Creates by all routers.
• Takes off the direct-connected
network prefix and connection type
list.
• Transmitted in the area and not
propagated beyond the ABR.
• The source identity of the LSA is
defined by the router ID of router.
• Sent to the multicast within the region
where they are produced.
İnternet
Area 1 Area 0 Area 2
ASBR ABR ABR
Type 1 Type 1 Type 1
Type 1
Type 2
• Define the network addresses of
routers and multiple access links.
• Creates by only DR routers.
• Transmitted within the multiple access
network and can not transimit beyond
the ABR.
defined by the router ID of DR router.
Type 2 Type 2
DR DR

Type 3
• They defines network address learned
by type 1 LSAs.
• Valid for each subnet.
• Transmitted between ABRs and
recreated by the transmitted ABR.
• The connection status is defined by
the network address.
• Routes are not summarized by default.
Type 4
• Used to introduce other areas to ASBR
and provide a route.
• Creates by ABR.
• The resource is created by ABR and
recreated by other ABRs.
defined by the router ID of ASBR
router.
İnternet
Area 1 Area 0 Area 2
ASBR ABR ABR
Type 3 Type 3 Type 3 Type 3
• Used to be notified by external network(e.g. Non-OSPF Networks).
• Creates by ASBR.
• Transmitted along the area and recreated by other ABRs.
• The source identity of the LSA is defined by the external network address.
• Routes are not summarized by default.
Type 5

Transition Between States
Down State
Init State
Two-Way State
ExStart State
Exchange State
Loading State
Full State
Setting
Up
Neighbors
Synchronize
OSPF
Databases
Hello packets not recieved yet, so router
sends to Hello packets.
Hello packets are taken from neighbor.
Packets contain the router ID of the
sending router.
One DR and one BDR are selected from
the Ethernet connection.
The router changes the DBD packets. If extra
routing information is required follow the
diagram. Otherwise go to Full State.
LSR and LSU are used to obtain additional
route information. Route are processed using
SPF algorithm.
Comlete mergers.
Starts the exchange of DBD packages.

Transition Between States On Scheme(cont.)
Lo0: 10.10.10.1
Fa 0/0:
192.168.1.1/24
Fa 0/0:
192.168.1.2/24
Fa 1/0:
172.16.1.1/24
Fa 1/0:
172.168.2.1/24
Lo0: 10.10.10.2
R1 R2
DOWN DOWN
I am 10.0.0.1. I see no one.
I am 10.0.0.1. I see 10.0.0.2
I am 10.0.0.2. I see 10.0.0.1
2-WAY
2-WAY
HELLO --- 224.0.0.5 (Multicast)
HELLO --- 192.168.1.2 (Unicast)
DR/BDR ELECTION
I am 10.0.0.1. I see 10.0.0.2
DR = 192.168.1.2 || BDR = 192.168.1.1
I am 10.0.0.1. I see 10.0.0.2
DR = 192.168.1.2 || BDR = 192.168.1.1
INIT
When an OSPF router has a higher Router ID or priority
than the existing DR or BDR, it does not preempt the
existing DR or BDR. This prevents the DR/BDR election
process from occurring whenever a new OSPF router joins
a broadcast network.
When an OSPF router joins a broadcast network which has
a DR and BDR elected, it will only establish adjacency and
enter into the FULL state with the DR and BDR. The
neighbor state with other non-DR/BDR neighboring
routers (DROTHERs) would stays in the 2-WAY state.

Lo0: 10.10.10.1
Fa 0/0:
192.168.1.1/24
Fa 0/0:
192.168.1.2/24
Fa 1/0:
172.168.2.1/24
Lo0: 10.10.10.2
R1 R2
EXSTART EXSTARTI am the Master and will start the Exchange.
Here is a summary of my link-state database
No, I am the Master as I have higher Router ID.
EXCHANGE EXCHANGE
DBD – 192.168.1.2 (Unicast)
DBD – 192.168.1.1 (Unicast)
DBD - 192.168.1.2 (Unicast)
(Seq = 2222, Init, More, Master)
(Seq = 1111, Init, More, Master)
(Seq = 1111, More, Slave)
Here is a summary of my link-state database.
(Seq = 1112, More, Master)
DBD – 192.168.1.1 (Unicast)
N times of DBD exchange
(Seq = xxxx, Slave)
(Seq = xxxx, Master)
DBD - 192.168.1.2 (Unicast)
DBD – 192.168.1.1 (Unicast)
The EXSTART state ends once the Master/Slave
relationship is determined.
Sequence numbers are being used to determine the
newness of link-state information.
The Master will send the next DBD packet only when the
previous DBD packet is acknowledged through a DBD
packet with the same sequence number from the Slave. If
the Master does not receive an acknowledgment for an
outstanding DBD packet within the RxmtInterval, it would
retransmit the previous DBD packet.
The Slave would send a DBD packet with the same
sequence number to acknowledge the receipt of a DBD
packet from the Master. Therefore, the last DBD packet is
always sent by the Slave.

Lo0: 10.10.10.1
Fa 0/0:
192.168.1.1/24
Fa 0/0:
192.168.1.2/24
Fa 1/0:
172.168.2.1/24
Lo0: 10.10.10.2
R1 R2
LOADING LOADINGI would like to have the complete entry for
Here is the complete entry for
I would like to have the complete entry for
FULL FULL
LSR – 192.168.1.2 (Unicast)
LSR – 192.168.1.1 (Unicast)
LSU - 192.168.1.2 (Unicast)
LSID 10.10.10.2, Type Router-LSA
Here is the complete entry for
LSU – 192.168.1.1 (Unicast)
Thanks for information
Thanks for information
LSAck – 192.168.1.2 (Unicast)
LSAck – 192.168.1.1 (Unicast)
Not all LSAs require explicit acknowledgment. When
routing update cross, in which 2 neighboring routers send
each other the same instance of LSA at about the same
time, the received LSA will be treated as an implicit
acknowledgment and no corresponding LSAck packet is
required.

Designated Router
The solution of managing the number of adjacencies in
the multi-access network and transferring LSAs is DR.
OSPF selects a DR as aggregation and distribution point
for sent and received LSAs. In case of DR failure, a BDR
is also selected. The BDR listens passively on this
exchange and maintains links with all directors. If DR
stops generating hello packets, BDR identifies itself and
assumes the DR role.
Other routers without DR or BDR become DROTHER
DR is notified when a new device is added and DR
forwards it to all routers. This prevents LSA packets from
consuming bandwidth.
Selection of DR/BDR
There are two different options to choose from:
• Highest priority (0-255)
• Highest router ID
SW
RID : 2.2.2.2
BDR
RID : 3.3.3.3
DR
192.168.1.0/28172.16.1.0/24
RID : 1.1.1.1
172.16.2.0/24
172.16.3.0/24
R1
R2
R3

Router identity
A router ID is required for each router in order to join
the OSPF domain. The router ID is used by the router
OSPF enabled to:
• Uniquely identify the router
• Participation in the selection of DR
The router identifies its identity according to one of
three criteria in accordance with the following order
of preference:
• Via router ID command
• Highest loopback
• Selects the highest valued active
IPv4 address of the physical
interfaces.
Is the router ID
configured?
Is the IPv4
loopback
interface
configured
NO Use as a router ID
YES
YES
NO
Use the configured highest IPv4 address

SO: 10.1.16.1/30
SO: 10.1.16.2/30
SO: 209.165.201.1/27
SO: 209.165.201.2/27
E1: 10.1.19.1/24
E0: 10.1.10.4/24
E0: 10.1.13.2/24
E1: 10.1.13.1/24
E1: 10.1.10.3/24
E1: 10.1.10.1/24
E0: 10.1.10.2/24
Lo0: 192.168.10.1/32
Lo0: 192.168.10.3/32
Lo0: 192.168.10.5/32
Application 1 - Topology
R1
R2
R6
R3
R4R5

Section 1 – Choose Router ID
ROUTER NAME ROUTER ID
192.168.10.5
209.165.201.1
10.1.10.1
192.168.10.3
192.168.10.1
209.165.201.2
R1
R2
R3
R4
R5
R6
NETWORK ROUTER
R2
R4
YOK
R1
YOK
10.1.10.0
10.1.13.0
10.1.16.0
10.1.19.0
209.165.201.0
Application – Features of DR, BDR and DRother
FEATURES OF WHAT ?
Uses 224.0.0.5 multicast addresses to listen to LSA’ s.
Send LSA’ s to all participating directors.
Passively listen to LSA’ s.
If the DR stops producing Hello Packets, it will promote itself.
LSA will not be sent to all routers in the network.
Uses 224.0.0.6 multicast addresses to send to LSA’ s.
DR BDR DRother

General Search Mask
OSPF design is classless. For this reason, the general
search mask must always be used. The general
search mask is generally the reverse of the subnet
mask configured in this interface, while defining the
interfaces involved in the routing process.
A general lookup mask is a 32-bit binary string used
by the router to determine which address bits are
used to examine a match. The binary 1 in a submask
equals 1 to a match and the binary 0 equals to not
match. The opposite is true for a global search mask:
Subnet Mask
General Search Mask
255.255.255.255
- 255.255.255.000
000.000.000.255
Subnet Mask
General Search Mask
255.255.255.255
- 255.255.255.240
Subnet Mask
General Search Mask
255.255.255.255
- 255.255.255.192
000.000.000.015
000.000.000.063
• 0 : Matches the corresponding bit value in the
address.
• 1 : Ignores the corresponding bit value in the
address.
The easiest way to calculate a global search mask is
to subtract the network subnet mask from
255.255.255.255.

Passive Interface
By default, OSPF messages are transmitted from all
OSPF-enabled interfaces. Sending unnecessary
messages in a LAN affects the network in three
ways:
• Inefficient use of bandwidth
• Inefficient use of resources
• Increased security vulnerability
Bandwidth
OSPF use cost as a metric. Low cost indicates a
better way than high cost. The cost of an interface is
inversely proportional to the bandwidth of the
interface.
COST
Reference bandwidth
Interface bandwidth
=
The bandwidth of all connected interfaces must be
the same. The default reference-bandwidth is 100
000 000 kb/s or 100 Gb/s.
Interface Type Cost
10 Gb/sn 1
1 Gb/sn 1
100 Mb/sn 1
10 Mb/sn 10
1.544 Mb/sn 64
128 Kb/sn 781
64 Kb/sn 1562

MD5 Authentication
Often routing systems can be attacked by routing
partners or by tampering with information carried
in the routing protocol. Tampered routing
information to each other often gives incorrect
information about to the system, to cause a
denial-of-service attack (DoS) or can be used to
pass information from the road that traffic would
normally not be transmitted. The consequences of
tampering with routing information are:
• Route traffic to create routing loops
• Route traffic for tracing from an unsecured
connection
• Guide traffic to trash
When neighbor authentication is configured on a
router, this route checks the identity of the source
of each routing update package it receives. This
mean, with the exchange of an authentication
key(sometimes known as a password) happens in
routers.
R1 R2
OSPF Update Packet
192.168.10.10/24
192.168.20.10/24
192.168.10.20/24
192.168.10.10/24
Secret Key
1HIjoı3IıjKK54Signature
The signature is
matching?
NO YES
ACCEPTTHROW

Is the neighbor
table correct?
Is the routing
table correct?
Does traffic
take desired
route?
Connectivity Issues due to routing?
Functionally Network?
YES
YES
YES
YES
NO
NO
NO
• Are the interfaces operational?
• Are the interfaces enable for OSPF?
• Does the OSPF area match?
• Is there an interface that is configured as passive?
SHOW COMMAND
• Show ip interface brief
• Show ip ospf interface
SHOW COMMAND
SHOW COMMAND
Troubleshooting

OSPF Network Types
OSPF’s functionality is different across several different network topology types. OSPF’s interaction with Frame Relay will be explained in
another section .
Broadcast Multi-Access – indicates a topology where broadcast occurs.
• Examples include Ethernet, Token Ring, and ATM.
• OSPF will elect DRs and BDRs.
• Traffic to DRs and BDRs is multicast to 224.0.0.6. Traffic from DRs and BDRs to other routers is multicast to 224.0.0.5.
• Neighbors do not need to be manually specified.
The default OSPF network type for Ethernet and Token Ring is Broadcast Multi-Access. To configure manually:
Router(config)# interface Ethernet 0
Router(config-if)# ip ospf network broadcast
Point-to-Point – indicates a topology where two routers are directly connected.
• An example would be a point-to-point T1.
• OSPF will not elect DRs and BDRs.
• All OSPF traffic is multicast to 224.0.0.5.
The default OSPF network type for T1’s (HDLC or PPP) and Point-to-Point Frame Relay is Point-to-Point. To
configure manually:
Router(config)# interface serial 0
Router(config-if)# encapsulation frame-relay
Router(config-if)# interface serial 0.1 point-to-point
Router(config-if)# frame-relay map ip 10.10.10.10 100 broadcast
Router(config-if)# ip ospf network point-to-point

OSPF Network Types(cont.)
Non-broadcast Multi-access Network (NBMA) – indicates a topology where one interface can connect to multiple
destinations; however, broadcasts cannot be sent across a NBMA network.
• An example would be Frame Relay.
• OSPF will elect DRs and BDRs.
• OSPF neighbors must be manually defined, thus All OSPF traffic is unicast instead of multicast.
The default OSPF network type for basic Frame Relay is Non-broadcast Multi-access Network (NBMA). To configure
manually:
Router(config-if)# frame-relay map ip 10.10.10.10 100
Router(config-if)# ip ospf network non-broadcast
Router(config)# router ospf 1
Router(config-router)# neighbor 10.10.10.10
Notice that the neighbor was manually specified, as multicasting is not allowed on an NBMA. However, the Frame-
Relay network can be tricked into allowing broadcasts, eliminating the need to manually specify neighbors:
Router(config-if)# ip ospf network broadcast
Notice that the ospf network type has been changed to broadcast, and the broadcast parameter was added to the
frame-relay map command. The neighbor no longer needs to be specified, as multicasts will be allowed out this
map.

Point-to-Multipoint – indicates a topology where one interface can connect to multiple destinations. Each connection between a source and
destination is treated as a point-to-point link.
• An example would be Point-to-Multipoint Frame Relay.
• OSPF will not elect DRs and BDRs.
• All OSPF traffic is multicast to 224.0.0.5.
The default OSPF network type for Point-to-Multipoint Frame Relay is still Non-broadcast Multi-access Network (NBMA). However, OSPF supports
an additional network type called Point-to-Multipoint, which will allow neighbor discovery to occur automatically. To configure:
OSPF Network Types(cont.)
Router(config)# interface serial 0.2 multipoint
Router(config-router)# ip ospf network point-to-multipoint
Router(config-if)# frame-relay map ip 10.10.10.10 100 broadcast
Additionally, a non-broadcast parameter can be added to the ip ospf network command when specifying point-to-multipoint.
Router(config)# interface serial 0.2 multipoint
Router(config-if)# ip ospf network point-to-multipoint non-broadcast
Router(config)# neighbor 10.10.10.10
Notice the different in configuration. The frame-relay map command no longer has the broadcast parameter, as broadcasts and multicasts are not
allowed on a non-broadcast network. Thus, in the OSPF router configuration, neighbors must again be manually specified. Traffic to those
neighbors will be unicast instead of multicast.

OSPF Route Types
External routes fall under two categories, external type 1 and external type 2. The difference between
the two is in the way the cost (metric) of the route is being calculated. The cost of a type 2 route is
always the external cost, irrespective of the interior cost to reach that route. A type 1 cost is the addition
of the external cost and the internal cost used to reach that route. A type 1 route is always preferred
over a type 2 route for the same destination.
İnternet
S0/0 : 192.168.1.2
S0/0 : 192.168.1.2
S0/0 : 192.168. 2.2
S0/1 : 192.168.2.1
RA RB RC
9.0.0.0 / 8
RIP
ASBR
AREA 0

External
Networks
R1
R2
R3
Area 1 Area 0
OSPF Route Types(cont.)
The ABRs and ASBRs of Standard areas do not automatically generate (or inject) default routes into the area. Consider the following example:
Assume that Area 1 is configured as a Standard area. Router 3 will forward Type 3 LSAs from all other areas into Area 1, allowing Router 1 and
Router 2 to reach inter-area networks.
Notice also that Router 1 is an ASBR, connecting to an external Autonomous System. Thus, Router 1 will generate Type 5 LSAs, detailing the routes
to these external networks.
To additionally force Router 1 to generate a default route (indicating itself as the next hop) for the external networks, and inject this into Area 1.
This default route will be advertised as a Type 5 LSA to all other areas:
Router 1 must have a default route in its routing table in order for the above command to function. Router 1’s default route would point to some
upstream router in the external Autonomous System.
Router(config)# default-information originate

OSPF Area Types Scheme
External
Networks
AREA 10 AREA 0 AREA 20
R1
R2
R3 R4
R5
R6
R7

OSPF Area Types(cont.)
In order to control the propagation of LSAs in the OSPF domain, several area types were developed.
Standart Area : A normal OSPF area.
• Routers within a standard area will share Router (Type 1) and Network (Type 2) LSAs to build their topology tables.
Once fully synchronized, routers within an area will all have identical topology tables.
• Standard areas will accept Network Summary (Type 3) LSAs, which contain the routes to reach networks in all other
areas.
• Standard areas will accept ASBR Summary (Type 4) and External (Type 5) LSAs, which contain the route to the ASBR and
routes to external networks, respectively.
Configuration of standard areas is straight forward:
Router(config-router)# network 10.1.0.0 0.0.7.255 area 1
Stub Area : Prevents external routes from flooding into an area.
• Like Standard areas, Stub area routers will share Type 1 and Type 2 LSAs to build their topology tables.
• Stub areas will also accept Type 3 LSAs to reach other areas.
• Stub areas will not accept Type 4 or Type 5 LSAs, detailing routes to external networks.
The purpose of Stub areas is to limit the number of LSAs flooded into the area, to conserve bandwidth and router CPUs. The
Stub’s ABR will automatically inject a default route into the Stub area, so that those routers can reach the external networks.
The ABR will be the next-hop for the default route.
Configuration of stub areas is relatively simple:
Router(config)# router 1 stub
The area 1 stub command must be configured on all routers in the Stub area. No ASBRs are allowed in a Stub area.

Totally Stubby Area : Prevents both inter-area and external routes from flooding into an area.
• Like Standard and Stub areas, Totally Stubby area routers will share Type 1 and Type 2 LSAs to build their
topology tables.
• Totally Stubby areas will not accept Type 3 LSAs to other areas.
• Totally Stubby areas will also not accept Type 4 or Type 5 LSAs, detailing routes to external networks.
Again, the purpose of Totally Stubby areas is to limit the number of LSAs flooded into the area, to conserve
bandwidth and router CPUs. The Stub’s ABR will instead automatically inject a default route into the Totally Stubby
area, so that those routers can reach both inter-area networks and external networks. The ABR will be the next-hop
for the default route.
Configuration of totally stubby areas is relatively simple:
Router(config-router)# area 1 stub no-summary
The area 1 stub no-summary command is configured only on the ABR of the Totally Stubby area; other routers
within the area are configured with the area 1 stub command. No ASBRs are allowed in a Totally Stubby area.
In the above example, if we were to configure Area 1 as a Totally Stubby area, it would not accept any external
routes originating from the ASBR (Router 7). It also would not accept any Type 3 LSAs containing route information
about Area 0 and Area 2. Instead, Router 3 (the ABR) will inject a default route into Area 1, and all routers within
Area 1 will use Router 3 as their gateway to all other networks.

Not So Stubby Area(NSSA) : Similar to a Stub area; prevents external routes from flooding into an area, unless those
external routes originated from an ASBR within the NSSA area
• Like Standard and Stub areas, NSSA area routers will share Type 1 and Type 2 LSAs to build their topology tables.
• NSSA areas will also accept Network Summary (Type 3) LSAs, which contain the routes to reach networks in all
other areas.
• NSSA areas will not accept Type 4 or Type 5 LSAs, detailing routes to external networks.
• If an ASBR exists within the NSSA area, that ASBR will generate Type 7 LSAs.
Again, NSSA areas are almost identical to Stub areas. If Area 1 was configured as an NSSA, it would not accept any
external routes originating from Router 7 (an ASBR outside Area 1). However, Area 1 also has an ASBR within the
area (Router 1). Those external routes will be flooded into Area 1 as Type 7 LSAs. These external routes will not be
forwarded to other areas as Type 7 LSAs; instead, they will be converted into Type 5 LSAs by Area 1’s ABR (Router 3).
Configuration of NSSA areas is relatively simple:
Router(config-router)# area 1 nssa
The area 1 nssa command must be applied to all routers in the NSSA area.

Totally Not So Stubby Area (TNSSA) : Similar to a Totally Stubby area; prevents both inter-area and external routes
from flooding into an area, unless those external routes originated from an ASBR within the NSSA area.
• Like Standard and Stub areas, TNSSA area routers will share Type 1 and Type 2 LSAs to build their topology tables.
• TNSSA areas will not accept Type 3 LSAs to other areas.
• TNSSA areas will not accept Type 4 or Type 5 LSAs, detailing routes to external networks.
• If an ASBR exists within the TNSSA area, that ASBR will generate Type 7 LSAs.
With the exception of not accepting inter-area routes, TNSSA areas are identical in function to NSSA areas.
Configuration of TNSSA areas is relatively simple:
Router(config-router)# area 1 nssa no-summary
The area 1 nssa no-summary command is configured only on the ABR of the TNSSA area; other routers within the area are
configured with the area 1 nssa command.

Application 2 - Topology
AREA 10 AREA 0 AREA 50
R1
R2
R3
R4
R5
R6
WEB
SERVER
ISP
SW-1
RID : 1.1.1.1
RID : 2.2.2.2
20.0.0.1
10.0.0.1
30.0.0.1
30.0.0.2
SW-0
30.0.0.3
40.0.0.1
100.0.0.1
40.0.0.2 50.0.0.1
50.0.0.2
100.0.0.2
60.0.0.1
60.0.0.2
70.0.0.1
70.0.0.2
80.0.0.2
80.0.0.1
90.0.0.2
90.0.0.1
The network infrastructure installation work of XXX Company was given to you. Accordingly, configure all PCs so that they can connect to the
Internet Server. Assign all subnet masks to 255.0.0.0.
RID : 3.3.3.3
RID : 4.4.4.4
RID : 5.5.5.5
RID : 6.6.6.6
PC1
PC2
PC3
20.0.0.2
10.0.0.2

Check Configuration on Routers
R4(config-if)# ip address 80.0.0.2 255.0.0.0
R4(config)# interface FastEthernet 0/0
First we will show the configurations to be made on a router. We will then share screenshots of the settings written on the company's
remaining devices. The output of the working company network, OSPF neighbors and various control / troubleshooting commands for
routing tables will be examined.
The R4 router with some extra settings has been chosen for this. As a reference, the following commands are used to configure the
settings on this router:
R4(config)# interface FastEthernet 0/1
R4(config)# interface Serial 0/0/0
R4(config-router)# network 50.0.0.0 0.0.0.255 area 0
R4(config)# router ospf 4
R4(config-router)# network 40.0.0.0 0.0.0.255 area 0
R4(config-router)# router-id 4.4.4.4
R4(config-router)# default-information-originate
R4(config)# ip route 0.0.0.0 0.0.0.0 80.0.0.1
All necessary IP configurations
were made on all active
interfaces
The default route was configured to access the web
server. This route was also taught on the OSPF
network(default-information-originate).
The required OSPF settings were made in the
router (eg router ID, networks to which it was
connected)

Check Configuration on Routers(cont.)
Configuration settings related to OSPF over R1; Configuration settings related to OSPF over R2;
In the meantime, extra features can be added on the Switch if desired. In this example Switch is used only as an
intermediate device. Adjustments can be configured for network complexity, security precautions, and so on.

Check Configuration on Routers(cont.)
Configuration settings related to OSPF over R5;Configuration settings related to OSPF over R3; Configuration settings related to OSPF over R6;

Troubleshooting on Router
Only the output of show commands on a single router(R4) will be examined. To view the OSPF Neighbor Table:
The Neighbor Table provides the following information about each neighbor:
• The Router ID of the remote neighbor.
• The OSPF priority of the remote neighbor (used for DR/BDR elections).
• The current neighbor state.
• The dead interval timer.
• The connecting IP address of the remote neighbor.
• The local interface connecting to the remote neighbor.

Troubleshooting on Router(cont.)
Only the output of show commands on a single router(R4) will be examined. To view the OSPF topology table:
The Topology Table provides the following information:
• The actual link (or route).
• The advertising Router ID.
• The link-state age timer.
• The sequence number and checksum for each entry.

Only the output of show commands on a single router(R4) will be examined. To view the specific information about an OSPF process:
The show ip ospf command provides the following information:
• The local Router ID.
• SPF Scheduling information, and various SPF timers.
• The number of interfaces in specific areas, including the type of area.
• The link-state age timer.
• The sequence number and checksum for each entry.

Only the output of show commands on a single router(R4) will be examined. To view routing protocol specific information for OSPF:
The show ip protocols command provides the following information:
• Locally originated networks that are being advertised.
• Neighboring sources for routing information
• The administrative distance of neighboring sources.

Only the output of show commands on a single router(R4) will be examined. To view OSPF-specific information on an interface:
The show ip ospf interface command provides the following information:
• The local Router ID.
• The interface network type.
• The OSPF cost for the interface.
• The interface Hello and Dead timers.
• A list of neighbor adjacencies.

OSPF Summarization
Summarization allows you to keep the routing tables small. Combines more than one route and then resulting in a single route published. They can
then be published into the spine area.
Typically, type 1 and type 2 LSAs are produced in-house in each field, converted to type 3 LSAs and sent to other fields. If there were 30 networks
to be introduced to area 1, into the spine 30 type 3 LSAs would be transmitted. The ABR combines 30 networks in an aggregate published with
route summarization.
Summarization helps to increase network stability as it reduces unnecessary LSA multicasting. This directly affects the bandwidth consumed by the
OSPF routing process, the amount of CPU and memory resources. Without route summarization, the transmission of each specific link to the OSPF
backbone and beyond has been done separately. This causes unnecessary network traffic and router workload.
In OSPF, summarization is only configured in ABRs or ASBRs. ABR routers type 3 LSAs; ABSR routers also summarize type 5 LSAs. Route
summarization can be configured in the following ways:
• Summarize route between areas - Inter area route summarization occurs in ABR and applies to routes of
each area. Not applicable for routes injected into OSPF by distribution. To perform an effective route
summarization between areas, must be assigned contiguous in such a way that it can be summarized as
at least a summary address.
• External route summarization - External route summarization is external rotala-specific injected into
OSPF via route distribution. Again, it is important to ensure the continuity of the external address space
to be summarized. Usually only ASBRs summarize external roots.

OSPF Summarization(cont.)
EIGRP
172.16.0.0/24
172.16.31.0/24
10.1.1.0/24 10.1.2.0/24 192.168.1.0/24 192.168.2.0/24
AREA 10 AREA 15
AREA 0
192.168.10.0/30
192.168.10.4/30
10.2.1.0/24
Send
summarization
route to
10.1.0.0/24

Calculating Route Summarization
10.1.1.0
10.1.2.0
00001010 . 00000001 . 00000001 . 00000000
00001010 . 00000001 . 00000010 . 00000000
10.1.1.0
255.255.252.0
00001010 . 00000001 . 00000000 . 00000000
11111111 . 11111111 . 11111100 . 00000000
Matching first 22 bits
/22
Different BitsStep 1 Step 2
Step 3
10.1.0.0/22 or 10.1.1.0 255.255.252.0
10.1.0.0/24
10.1.1.0/24
10.1.2.0/24
10.1.3.0/24
The obtained 10.1.0.0/22 route was summarized together with 4 different
networks. In the example, the summary address matches 4 networks, although
there are only 2 networks.

Sources
1. İtcertnotes
2. Router Alley
3. Cisco
4. Etherealmind
5. 9tut

Dynamic Routing Protocol OSPF

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Dynamic Routing Protocol OSPF

Similar to Dynamic Routing Protocol OSPF (20)

Recently uploaded

Recently uploaded (20)

Dynamic Routing Protocol OSPF

Editor's Notes