ConfigureTwo networks principle

Implemention principles of East ToImplemention principles of East To
West NetworksWest Networks
Dr Ahmed Alneami
British Institute of Technology and E-Commerce
email:- drahmed@bite.ac.uk
Web:- www.bite.ac.uk

NetworkTechnologyNetworkTechnology
Final AssignmentFinal Assignment
Submission Date: 6th of Dec. 2010
Configure a new network between East and West
London branches through a headquater.
East
London
West
LondonHeadquarter

Outcomes of this lecture are:Outcomes of this lecture are:
1. Scalable Routing Protocols and (Scalable
network)
2. TCP/IP (Transmission Control
Protocol/Internet Protocol)
3. OSPF (Open Shortest Path First)
4. or BGP (Border Gateway Protocol)
5. DHCP (Dynamic Host Configuration
Protocol)
6. NAT (Network Address Translation)

Web 2.0 Expo NYC, 16th
September 2008 4
Scalability – myths and liesScalability – myths and lies
What is scalability not ?
◦ Raw Speed / Performance
◦ HA / BCP
◦ Technology X
◦ ProtocolY

September 2008 5
So what is scalability?

September 2008 6
So what is scalability?
◦ Traffic growth
◦ Dataset growth
◦ Maintainability

September 2008 7
TodayToday
Two goals of application architecture:
Scale
HA

September 2008 8
TodayToday
Three goals of application architecture:
Scale
HA
Performance

September 2008 9
ScalabilityScalability
Two kinds:
◦ Vertical (get bigger)
◦ Horizontal (get more)
Network Scalability it is a a routing protocol developed for IP NKs.
i.e Without a scalable routing system, a Nk may suffer from severe
peformance penalties and proven by disastorus events in large
network.

September 2008 10
Big IronsBig Irons
Sunfire E20k
$450,000 - $2,500,000
36x 1.8GHz processors
PowerEdge SC1435
Dualcore 1.8 GHz processor
Around $1,500

September 2008 11
Cost vs CostCost vs Cost
See the uploaded
Scalable –Rep file please.

Routing Information ProtocolRouting Information Protocol
RIPRIP
identify the best path to any given
destination address.
As IP-based networks became both more
numerous and greater in size, it became
apparent to the Internet Engineering Task
Force (IETF) that RIP needed to be updated.
RIP 2 enabled RIP messages to carry more
information, which permitted the use of a
simple authentication mechanism to secure
table updates.

13
Router
Router
Router
Router Router
What is
an optimal
route ?
What is
an optimal
route ?
Switch
Switch
Routing Protocol

RIP Routing Metric
•RIP uses a single routing metric (hop count) to measure the
distance between the source and a destination network.
•The IP address of the sender is used as the next hop.
•RIP prevents routing loops from continuing indefinitely by
implementing a limit on the number of hops allowed in a path from
the source to a destination. Max 16
•RIP uses numerous timers to regulate its performance. These
include a routing-update timer, a route-timeout timer, and a
route-flush timer.

IP RIP packet format fields
Command—Indicates whether the packet is a request or a response. The
request asks that a router send all or part of its routing table.
•Zero—This field is not actually used by RFC 1058 RIP; it was added solely to
provide backward compatibility with prestandard varieties of RIP. Its name
comes from its defaulted value: zero.
•Address-family identifier (AFI)—Specifies the address family used.
Each entry has an address-family identifier to indicate the type of address being
specified.
•Address—Specifies the IP address for the entry.
•Metric—Indicates how many internetwork hops (routers) have been traversed
in the trip to the destination. This value is between 1 and 15 for a valid route, or
16 for an unreachable route.
•Version number—Specifies the RIP version used. This field can signal different
potentially incompatible versions.
See the uploaded RIP file please.

The Open Shortest Path FirstThe Open Shortest Path First
(OSPF) protocol(OSPF) protocol
How OSPF works and how it can be used to design
and build large and complicated networks.

Background InformationBackground Information
It was found that Routing Information
Protocol (RIP) incabable in serving the
large hetrogeneous internetworks.

The Intermediate System-to-The Intermediate System-to-
Intermediate System (IS-IS) routingIntermediate System (IS-IS) routing
protocolprotocol
The (IS-IS) routing protocol is an Interior
Gateway Protocol (IGP) standardized by the
Internet Engineering Task Force (IETF).
 Commonly used in large Service Provider
networks.
IS-IS may also be deployed in extremely large
Enterprise networks.
IS-IS is a link-state routing protocol, providing fast
convergence and excellent scalability.
Like all link-state protocols, IS-IS is very efficient
in its use of network bandwidth.

Intermediate Systems-to-Intermediate Systems-to-
Intermediate Systems IS-ISIntermediate Systems IS-IS
This is dynamic link state routing
protocol
All Intermediate Systems are routers,
Routers are organised into local groups
called Areas,
Several Areas are grouped together into a
“Domain”,
IS-IS places area router into layer (no. 1)
and the routers that interconnected the
areas into layer 2.

Backbone Area (area 0) is the first area
that will always exist in any network using
OSPF.
All other areas are connected to be the
backbone either Directly or usingVirtual
Links that “tunnel” through other areas.
Each area is designated by an area
number.
All other areas described as having
stubbiness

22
Path Determination GraphicPath Determination Graphic

23
Router
Router
Router
Router Router
What is
an optimal
route ?
What is
an optimal
route ?
Switch
Switch
Routing Protocol

24
Routing ProtocolsRouting Protocols
Routing protocols
includes the following:
processes for sharing
route information allows
routers to communicate
with other routers to
update and maintain the
routing tables
Examples of routing
protocols that support
the IP routed protocol
are:
RIP, IGRP,
OSPF, BGP,
and EIGRP.

25
Routed ProtocolsRouted Protocols
Protocols used at the network layer that transfer data from one host to another across a
router are called routed or routable protocols. The Internet Protocol (IP) and Novell's
Internetwork Packet Exchange (IPX) are examples of routed protocols. Routers use routing
protocols to exchange routing tables and share routing information. In other words, routing
protocols enable routers to route routed protocols.

26
Autonomous System
AS 2000
AS 3000
IGP
Interior Gateway Protocols are
used for routing decisions
within an Autonomous System.
Exterior Gateway
Protocols are used
for routing between
Autonomous Systems
EGP
AS 1000
An Autonomous System (AS) is a group of IP networks, which has a
single and clearly defined external routing policy.
Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67)

27
IGP
Interior Gateway Protocol
(IGP)
Exterior Gateway
Protocol (EGP)
EGP
EGP
EGP
Interior Gateway Protocol
(IGP)
AS 1000
AS 2000
AS 3000
Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67)

28
IGP and EGPIGP and EGP
An autonomous system is a network or set of networks under
common administrative control, such as the cisco.com domain.

29
Categories of Routing ProtocolsCategories of Routing Protocols
Most routing algorithms can be classified into one of two categories:
• distance vector
• link-state
The distance vector routing approach determines the direction
(vector) and distance to any link in the internetwork.
The link-state approach, also called shortest path first, recreates the
exact topology of the entire internetwork.

30
DistanceVectorDistanceVector
Routing ConceptsRouting Concepts

31
2 Hops
1 Hop1 Hop
Destination
192.16.1.0
192.16.5.0
192.16.7.0
Distance
1
1
2
Routing table contains the addresses
of destinations and the distance
of the way to this destination.
Flow of routing
information
Flow of routing
information
Router B Router CRouter A Router D
192.16.1.0192.16.1.0 192.16.7.0192.16.7.0
192.16.5.0192.16.5.0
Distance Vector Routing (DVR)

32
RoutingTables GraphicRoutingTables Graphic

33
DistanceVectorDistanceVector
Topology ChangesTopology Changes

34
Router Metric ComponentsRouter Metric Components

35
RIPv1
Distance Vector Routing Protocol,
classful
Distribution of Routing Tables via broadcast
to adjacent routers
Only one kind of metric:
Number of Hops
Connections with different
bandwidth can not be weighted
Routing loops can occur
-> bad convergence in case of a failure
Count to infinity problem
(infinity = 16)
Maximum network size is limited
by the number of hops
Fig.59PropertiesofRIPv1(TI1332EU02TI_0004TheNetworkLayer,81)

36
RIP CharacteristicsRIP Characteristics

37
200.14.13.0/24200.14.13.0/24
130.24.13.0/24130.24.13.0/24
Router A
Port 2
200.14.13.2/24
Port 2
200.14.13.2/24
Port 1
130.24.13.1/24
Port 1
130.24.13.1/24
130.24.36.0/24130.24.36.0/24
RIP-1: 130.24.36.0 RIP-1: 130.24.36.0
RIP-1: 130.24.0.0
130.24.25.0/24130.24.25.0/24
RIP-1 permits only a Single Subnet Mask
Fig. 60 RIP-1 permits only a single subnet mask (TI1332EU02TI_0004 The Network Layer, 83)

38
Router ConfigurationRouter Configuration
The router command starts a routing process.
The network command is required because it enables the routing
process to determine which interfaces participate in the sending and
receiving of routing updates.
An example of a routing configuration is:
GAD(config)#router rip
GAD(config-router)#network 172.16.0.0
The network numbers are based on the network class addresses,
not subnet addresses or individual host addresses.

39
Configuring RIP ExampleConfiguring RIP Example

40
Verifying RIP ConfigurationVerifying RIP Configuration

41
The debug ip rip CommandThe debug ip rip Command
Most of the RIP
configuration errors
involve an incorrect
network statement,
discontiguous
subnets, or split
horizons. One
highly effective
command for
finding RIP update
issues is the debug
ip rip command.
The debug ip rip
command displays
RIP routing updates
as they are sent and
received.

42
Problem: Routing LoopsProblem: Routing Loops
Routing loops
can occur when
inconsistent
routing tables
are not updated
due to slow
convergence in
a changing
network.

43
Problem: Counting to InfinityProblem: Counting to Infinity

44
Solution: Define a MaximumSolution: Define a Maximum

45
Solution: Split HorizonSolution: Split Horizon

46
NATNAT
Network AddressTranslatorNetwork AddressTranslator
Fig. 3 NAT (TI1332EU02TI_0003 New Address Concepts, 7)

47
New addressing concepts
Problems with IPv4
Shortage of IPv4 addresses
Allocation of the last IPv4 addresses is forecasted for the year 2005
Address classes were replaced by usage of CIDR, but this is not sufficient
Short term solution
NAT: Network Address Translator
Long term solution
IPv6 = IPng (IP next generation)
Provides an extended address range
Fig. 2 Address shortage and possible solutions (TI1332EU02TI_0003 New Address Concepts, 5)

48
NAT
Translates between local addresses and public ones
Many private hosts share few global addresses
Public Network
Uses public addresses
Public addresses are
globally unique
Private Network
Uses private address range
(local addresses)
Local addresses may not
be used externally
Fig. 4 How does NAT work? (TI1332EU02TI_0003 New Address Concepts, 9)

49
NAT
To be
translated
exclude
reserve
pool
exclude
realm with
private addresses
NAT Router
realm with
public addresses
map
translate
Fig. 5 Translation mechanism (TI1332EU02TI_0003 New Address Concepts, 9)

50
free
NAT
Pool
A timeout value (default 15 min) instructs NAT
how long to keep an association in an idle state before
returning the external IP address to the free NAT pool.
Fig. 8 How does NAT know when to return the public IP address to the pool? (TI1332EU02TI_0003 New Address Concepts, 15)

51
NAT Addressing TermsNAT Addressing Terms
Inside Local
◦ The term “inside” refers to an address used for a host inside
an enterprise. It is the actual IP address assigned to a host in
the private enterprise network.
Inside Global
◦ NAT uses an inside global address to represent the inside
host as the packet is sent through the outside network,
typically the Internet.
◦ A NAT router changes the source IP address of a packet
sent by an inside host from an inside local address to an
inside global address as the packet goes from the inside to
the outside network.

52
Outside Global
◦ The term “outside” refers to an address used for a host
outside an enterprise, the Internet.
◦ An outside global is the actual IP address assigned to a host
that resides in the outside network, typically the Internet.
Outside Local
◦ NAT uses an outside local address to represent the outside
host as the packet is sent through the private enterprise
network.
◦ A NAT router changes a packet’s destination IP address,
sent from an outside global address to an inside host, as the
packet goes from the outside to the inside network.

53
SIEMENSNIXDORF
10.47.10.10 192.50.20.5
WAN
Net
A
Net B
SIEMENSNIXDORF
LAN LAN
192.50.20.0
10.0.0.0
Router Router
RouterRouter
Router
SA = 10.47.10.10SA = 10.47.10.10
DA = 192.50.20.5DA = 192.50.20.5
SA = 193.50.30.4SA = 193.50.30.4
DA = 192.50.20.5DA = 192.50.20.5
Router A with NATRouter A with NAT
Router BRouter B
Fig. 7 An example for NAT (TI1332EU02TI_0003 New Address Concepts, 13)

54
WAN
138.76.29.7
SIEMENSNIXDORF
Net A
10.0.0.0/8
Router
Router
Router
SA = 10.0.0.10SA = 10.0.0.10
DA = 138.76.29.7DA = 138.76.29.7
SA = 138.76.28.4SA = 138.76.28.4
DA =138.76.29.7DA =138.76.29.7
NAT with
WAN interface:
138.76.28.4
NAT with
WAN interface:
138.76.28.4
SA = 138.76.29.7SA = 138.76.29.7
DA = 138.76.28.4DA = 138.76.28.4
SA = 138.76.29.7SA = 138.76.29.7
DA = 10.0.0.10DA = 10.0.0.10
10.0.0.10
SIEMENSNIXDORF
Fig. 11 An example for NAPT (TI1332EU02TI_0003 New Address Concepts, 21)

55
Types Of NATTypes Of NAT
There are different types of NAT that can
be used, which are
◦ Static NAT
◦ Dynamic NAT
◦ Overloading NAT with PAT (NAPT)

56
Static NATStatic NAT
With static NAT, the NAT router simply
configures a one-to-one mapping between
the private address and the registered
address that is used on its behalf.

57
Dynamic NATDynamic NAT
Like static NAT, the NAT router creates a
one-to-one mapping between an inside
local and inside global address and
changes the IP addresses in packets as
they exit and enter the inside network.
However, the mapping of an inside local
address to an inside global address
happens dynamically.

58
Dynamic NATDynamic NAT
Dynamic NAT sets up a pool of possible inside
global addresses and defines criteria for the set
of inside local IP addresses whose traffic should
be translated with NAT.
The dynamic entry in the NAT table stays in
there as long as traffic flows occasionally.
If a new packet arrives, and it needs a NAT
entry, but all the pooled IP addresses are in use,
the router simply discards the packet.

59
PATPAT
Port Address TranslatorPort Address Translator
Fig. 9 NAPT (TI1332EU02TI_0003 New Address Concepts, 17)

60
WAN
138.76.29.7
SIEMENSNIXDORF
Net A
10.0.0.0/8
Router
Router
Router
SA = 10.0.0.10, sport = 3017SA = 10.0.0.10, sport = 3017
DA = 138.76.29.7, dpor t= 23DA = 138.76.29.7, dpor t= 23
SA = 138.76.28.4, sport = 1024SA = 138.76.28.4, sport = 1024
DA =138.76.29.7, dpor t= 23DA =138.76.29.7, dpor t= 23
NAPT with
WAN interface:
138.76.28.4
NAPT with
WAN interface:
138.76.28.4
SA = 138.76.29.7, spor t= 23SA = 138.76.29.7, spor t= 23
DA = 138.76.28.4, dport = 1024DA = 138.76.28.4, dport = 1024
SA = 138.76.29.7, spor t= 23SA = 138.76.29.7, spor t= 23
DA = 10.0.0.10, dport = 3017DA = 10.0.0.10, dport = 3017
10.0.0.10
SIEMENSNIXDORF
Fig. 11 An example for NAPT (TI1332EU02TI_0003 New Address Concepts, 21)

61
WAN
private IP network
(e.g. SOHO)
registered IP @,
assigned TU port #
local IP @,
local TU port #
single public
IP address
mapping
pool of TU port numbers
PAT with e.g. a single public IP addressPAT with e.g. a single public IP address
TU....TCP/UDP
Fig. 10 NAPT (TI1332EU02TI_0003 New Address Concepts, 19)

62
NAT&PATNAT&PAT
Network Address Translation &Network Address Translation &
Port Address TransationPort Address Transation
Fig. 3 NAT (TI1332EU02TI_0003 New Address Concepts, 7)

63
New addressing concepts
Problems with IPv4
Shortage of IPv4 addresses
Allocation of the last IPv4 addresses is forecasted for the year 2006
Address classes were replaced by usage of CIDR, but this is not sufficient
Short term solution
Long term solution
IPv6 = IPng (IP next generation)
Provides an extended address range

64
NAT
Translates between local addresses and public ones
Many private hosts share few global addresses
Public Network
Uses public addresses
Public addresses are
globally unique
Private Network
Uses private address range
(local addresses)
Local addresses may not
be used externally
Fig. 4 How does NAT work? (TI1332EU02TI_0003 New Address Concepts, 9)

65
NAT
To be
translated
exclude
reserve
pool
exclude
private addresses
NAT Router
public addresses
map
translate
Fig. 5 Translation mechanism (TI1332EU02TI_0003 New Address Concepts, 9)

66
free
NAT
Pool
A timeout value (default 15 min) instructs NAT
how long to keep an association in an idle state before
returning the external IP address to the free NAT pool.
Fig. 8 How does NAT know when to return the public IP address to the pool? (TI1332EU02TI_0003 New Address Concepts, 15)

67
Inside Local “Private address”
◦ The term “inside” refers to an address used for a host inside
an enterprise. It is the actual IP address assigned to a host in
the private enterprise network.
Inside Global “Public address”
◦ NAT uses an inside global address to represent the inside
host as the packet is sent through the outside network,
typically the WAN.
◦ A NAT router changes the source IP address of a packet
sent by an inside host from an inside local address to an
inside global address as the packet goes from the inside to
the outside network.

OSPF (Open Shortest Path First)
Protocol
© 2003, Cisco Systems, Inc. All rights reserved. 68

69
OSPF is a Link-OSPF is a Link-SState Routing Protocolstate Routing Protocols
◦ Link-state (LS) routers recognize much more information about
the network than their distance-vector counterparts,Consequently LS
routers tend to make more accurate decisions.
◦ Link-state routers keep track of the following:
 Their neighbours
 All routers within the same area
 Best paths toward a destination

70
Link-Link-SState Data Structurestate Data Structures
◦ Neighbor table:
 Also known as the adjacency database
(list of recognized neighbors)
◦ Topology table:
 Typically referred to as LSDB
(routers and links in the area or network)
 All routers within an area have an identical LSDB
◦ Routing table:
 Commonly named a forwarding database
(list of best paths to destinations)

71
OSPF vs. RIPOSPF vs. RIP
RIP is limited to 15 hops, it converges slowly, and it sometimes chooses slow
routes because it ignores critical factors such as bandwidth in route
determination. OSPF overcomes these limitations and proves to be a robust
and scalable routing protocol suitable for the networks of today.

72
OSPFTerminologyOSPFTerminology
The next several slides explain various OSPF terms -one
per slide.

73
OSPFTerm: LinkOSPFTerm: Link

74
OSPFTerm: Link StateOSPFTerm: Link State

75
OSPFTerm: AreaOSPFTerm: Area

76
OSPFTerm: Link CostOSPFTerm: Link Cost

77
OSPFTerm: Forwarding DatabaseOSPFTerm: Forwarding Database

78
OSPFTerm: Adjacencies DatabaseOSPFTerm: Adjacencies Database

79
OSPFTerms: DR & BDROSPFTerms: DR & BDR

80
LLink-ink-SStatetate Data StructureData Structure::
Network HierarchyNetwork Hierarchy
Link-state routing requires a hierachical
network structure that is enforced by OSPF.
This two-level hierarchy consists of the
following:
 Transit area (backbone or area 0)
 Regular areas (nonbackbone areas)

83
LS Data StructureLS Data Structuress:: AdjacencyAdjacency
DatabaseDatabase
◦ Routers discover neighbors by exchanging
hello packets.
◦ Routers declare neighbors to be up after checking
certain parameters or options in the hello packet.
◦ Point-to-point WAN links:
 Both neighbors become fully adjacent.
◦ LAN links:
 Neighbors form an adjacency with the DR and BDR.
 Maintain two-way state with the other routers (DROTHERs).
◦ Routing updates and topology information are only passed between
adjacent routers.

84
OSPF Adjacencies
Routers build logical adjacencies between each other using
the Hello Protocol. Once an adjacency is formed:
• LS database packets are exchanged to synchronize
each other’s LS databases.
• LSAs are flooded reliably throughout the area or network
using these adjacencies.

85
Open Shortest Path FirstOpen Shortest Path First
CalculationCalculation
Routers find the best paths to destinations by applying
Dijkstra’s SPF algorithm to the link-state database as
follows:
◦ Every router in an area has the identical
link-state database.
◦ Each router in the area places itself into
the root of the tree that is built.
◦ The best path is calculated with respect to the
lowest total cost of links to a specific destination.
◦ Best routes are put into the forwarding database.

89
Establishing Bidirectional
Communication

90
Communication (Cont.)

91
Communication (Cont.)

92
Communication

93
Discovering the Network Routes

94
Discovering the Network Routes

95
Adding the Link-State Entries

96
Adding the Link-State Entries (Cont.)

97
Adding the Link-State Entries

98
Maintaining Routing Information
• Router A notifies all OSPF DRs on 224.0.0.6

99
(Cont.)
• DR notifies others on 224.0.0.5

100
(Cont.)

101

102
router ospf process-idrouter ospf process-id
Router(config)#
• Turns on one or more OSPF routing processes in
the IOS software.
Configuring Basic OSPF: Single AreaConfiguring Basic OSPF: Single Area
network address inverse-mask area [area-id]network address inverse-mask area [area-id]
Router(config-router)#
• Router OSPF subordinate command that defines
the interfaces (by network number) that OSPF
will run on. Each network number must be
defined to a specific area.

103
Configuring OSPF on Internal
Routers of a Single Area

104
show ip protocolsshow ip protocols
Router#
• Verifies the configured IP routing protocol
processes, parameters and statistics
Verifying OSPF OperationVerifying OSPF Operation
show ip route ospfshow ip route ospf
Router#
• Displays all OSPF routes learned by the router
show ip ospf interfaceshow ip ospf interface
Router#
• Displays the OSPF router ID, area ID and
adjacency information

105
show ip ospfshow ip ospf
Router#
• Displays the OSPF router ID, timers, and statistics
Verifying OSPF Operation (Cont.)Verifying OSPF Operation (Cont.)
show ip ospf neighbor [detail]show ip ospf neighbor [detail]
Router#
• Displays information about the OSPF neighbors,
including Designated Router (DR) and Backup
Designated Router (BDR) information on
broadcast networks

106
The show ip route ospf CommandThe show ip route ospf Command
RouterA# show ip route ospf
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,
B - BGP, D - EIGRP, EX - EIGRP external, O - OSPF,
IA - OSPF inter area, E1 - OSPF external type 1,
E2 - OSPF external type 2, E - EGP, i - IS-IS, L1 - IS-IS
level-1, L2 - IS-IS level-2, * - candidate default
Gateway of last resort is not set
10.0.0.0 255.255.255.0 is subnetted, 2 subnets
O 10.2.1.0 [110/10] via 10.64.0.2, 00:00:50, Ethernet0

107
The show ip ospf interface CommandThe show ip ospf interface Command
RouterA# show ip ospf interface e0
Ethernet0 is up, line protocol is up
Internet Address 10.64.0.1/24, Area 0
Process ID 1, Router ID 10.64.0.1, Network Type BROADCAST, Cost: 10
Transmit Delay is 1 sec, State DROTHER, Priority 1
Designated Router (ID) 10.64.0.2, Interface address 10.64.0.2
Backup Designated router (ID) 10.64.0.1, Interface address 10.64.0.1
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:04
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 10.64.0.2 (Designated Router)
Suppress hello for 0 neighbor(s)

108
The show ip ospf neighbor CommandThe show ip ospf neighbor Command
RouterB# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.64.1.1 1 FULL/BDR 00:00:31 10.64.1.1 Ethernet0
10.2.1.1 1 FULL/- 00:00:38 10.2.1.1 Serial0

109
show ip protocolshow ip protocol
show ip route

110
show ip ospf neighbor detailshow ip ospf neighbor detail
show ip ospf database

111
OSPF NetworkTypes - 1OSPF NetworkTypes - 1

112
Point-to-Point Links
• Usually a serial interface running either PPP
or HDLC
• May also be a point-to-point subinterface
running Frame Relay or ATM
• No DR or BDR election required
• OSPF autodetects this interface type
• OSPF packets are sent using multicast 224.0.0.5

113
Multi-access Broadcast Network
• Generally LAN technologies like Ethernet and Token Ring
• DR and BDR selection required
• All neighbor routers form full adjacencies with the DR and
BDR only
• Packets to the DR use 224.0.0.6
• Packets from DR to all other routers use 224.0.0.5

114
Electing the DR and BDR
• Hello packets are exchanged via IP multicast.
• The router with the highest OSPF priority is
selected as the DR.
• Use the OSPF router ID as the tie breaker.
• The DR election is nonpreemptive.

115
Setting Priority for DR ElectionSetting Priority for DR Election
ip ospf priority numberip ospf priority number
• This interface configuration command assigns the
OSPF priority to an interface.
• Different interfaces on a router may be assigned
different values.
• The default priority is 1. The range is from 0 to 255.
• 0 means the router is a DROTHER; it can’t be the
DR or BDR.
Router(config-if)#

116
OSPF NetworkTypes - 2OSPF NetworkTypes - 2

117
Creation of AdjacenciesCreation of Adjacencies
RouterA# debug ip ospf adj
Point-to-point interfaces coming up: No election
%LINK-3-UPDOWN: Interface Serial1, changed state to up
OSPF: Interface Serial1 going Up
OSPF: Rcv hello from 192.168.0.11 area 0 from Serial1 10.1.1.2
OSPF: End of hello processing
OSPF: Build router LSA for area 0, router ID 192.168.0.10
OSPF: Rcv DBD from 192.168.0.11 on Serial1 seq 0x20C4 opt 0x2 flag 0x7 len 32
state INIT
OSPF: 2 Way Communication to 192.168.0.11 on Serial1, state 2WAY
OSPF: Send DBD to 192.168.0.11 on Serial1 seq 0x167F opt 0x2 flag 0x7 len 32
OSPF: NBR Negotiation Done. We are the SLAVE
OSPF: Send DBD to 192.168.0.11 on Serial1 seq 0x20C4 opt 0x2 flag 0x2 len 72

118
Creation of Adjacencies (Cont.)Creation of Adjacencies (Cont.)
RouterA# debug ip ospf adj
Ethernet interface coming up: Election
OSPF: 2 Way Communication to 192.168.0.10 on Ethernet0, state 2WAY
OSPF: end of Wait on interface Ethernet0
OSPF: DR/BDR election on Ethernet0
OSPF: Elect BDR 192.168.0.12
OSPF: Elect DR 192.168.0.12
DR: 192.168.0.12 (Id) BDR: 192.168.0.12 (Id)
OSPF: Send DBD to 192.168.0.12 on Ethernet0 seq 0x546 opt 0x2 flag 0x7 len 32
<…>
OSPF: DR/BDR election on Ethernet0
OSPF: Elect BDR 192.168.0.11
OSPF: Elect DR 192.168.0.12
DR: 192.168.0.12 (Id) BDR: 192.168.0.11 (Id)

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