(Open Shortest Path First Protocol)bayanbox.ir/view/842381385731649203/ospf.pdf · OSPF IS-IS BGP...
Transcript of (Open Shortest Path First Protocol)bayanbox.ir/view/842381385731649203/ospf.pdf · OSPF IS-IS BGP...
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
1© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF(Open Shortest Path First
Protocol)
Kevin Chi ������������
Cisco Systems.
222© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Agenda
• OSPF Overview
• OSPF Terminology
• OSPF Operation
• Multiple OSPF Area
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
333© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
A day in a life of a router
- Find path
- Forward packet, forward packet, forward packet, forward packet...
- Find alternate path
- Forward packet, forward packet, forward packet, forward packet…
- Repeat until powered off
444© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Routing versus Forwarding
• Routing = building maps and giving directions
• Forwarding = moving packets between interfaces according to the “ directions”
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
555© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
IP Routing - finding the path
• Path derived from information received from a routing protocol
• Several alternative paths may exist
best next hop stored in forwarding table
• Decisions are updated periodically or as topology changes (event driven)
• Decisions are based on:
topology, policies and metrics (hop count, filtering, delay, bandwidth, etc.)
666© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
• Static routes
• Default routes
• Dynamic routing
IP Routing Learns Destinations
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
777© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Static Routes
• Routes configured manually
• Useful when few or just one route exist
• Can be administrative burden
• Frequently used for default route
888© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Default Routes
• Route used if no match is found inforwarding table
• Can be carried by routing protocols
• Two modelsSpecial network number:
0.0.0.0 (IP)
Flagged in routing protocolRIP, RIPv2 : network 0.0.0.0
IGRP, EIGRP : ip default-network
OSPF,ISIS : default originate
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
999© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Dynamic Routing - Routing Protocol Goals
• Optimal path selection
• Loop-free routing
• Fast convergence
• Limited design administration
• Minimize update traffic
• Handle address limitations
• Support hierarchical topology
• Incorporate rapid convergence
• Easy to configure
• Adapts to changes easily and quickly
• Does not create a lot of traffic
• Scales to a large size
• Compatible with existing hosts and routers
• Supports variable length subnet masks and discontiguous subnets
• Supports policy routing
101010© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
NameName
RIPRIP
RIPv2RIPv2
IGRPIGRP
EIGRPEIGRP
OSPFOSPF
IS-ISIS-IS
BGPBGP
TypeType
DVDV
DVDV
DVDV
Adv DVAdv DV
LSLS
LSLS
Path VecPath Vec
ProprietaryProprietary
NoNo
NoNo
YesYes
YesYes
NoNo
NoNo
NoNo
FunctionFunction
InteriorInterior
InteriorInterior
InteriorInterior
InteriorInterior
InteriorInterior
InteriorInterior
ExteriorExterior
UpdatesUpdates
30 Sec30 Sec
30 Sec30 Sec
90 Sec90 Sec
TrigTrig
TrigTrig
TrigTrig
IncrIncr
MetricMetric
HopsHops
HopsHops
CompComp
CompComp
CostCost
CostCost
N/AN/A
VLSMVLSM
NoNo
YesYes
NoNo
YesYes
YesYes
YesYes
SummSumm
AutoAuto
AutoAuto
AutoAuto
BothBoth
ManMan
AutoAuto
AutoAuto
• IP routing protocols are characterized as
YesYes
Internet Routing Protocols
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
111111© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
IP RIP
• Routing Information Protocol
• Widely available
• Hop count metric
• Periodic update
• Easy to implement
• One of the first available
• RFC 1058
• Simple = limited
• Slow convergence
• No VLSM
• No discontiguous subnets
• Max 15 Hops
121212© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
• Scalability concerns:ConvergenceUpdate trafficMetric limitations
Distance Vector
B DCA
Update Interval
RoutingTable
RoutingTable
Update Interval
RoutingTable
Update Interval
RoutingTable
B RoutingUpdate
DCAA CB D
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
131313© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
R1
R2
R3
T1
56k
T1
1 Hop Hops
RIP Metric
0 Hops
Path I
Path IIHost A
Host B
Host A sends traffic to Host B
141414© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
.6
.13
.9
.10.14
.5
A
C
B172.16172.16.40.1
255.255.255.0
172172.16.50.1255.255.255.0
172.16.60.1255.255.255.0
192.168.1.8255.255.255.252
192.168.1.4255.255.255.252
192.168.1.12255.255.255.252
Where Is 172.16.0.0?
Discontiguous IP Subnet
Routing Protocols will by DefaultSummarize Major Networks
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
151515© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
.6
.13
.9
.10.14
.5
A
C
B172.16.40.1
255.255.255.0
172.16.50.1255.255.255.0
172.16.60.1255.255.255.0
172.16.1.8255.255.255.252
172.16.1.4255.255.255.252
172.16.1.12255.255.255.252
VLSM : Variable Length Subnet Mask
Conserve IP Addresses
172.16.1.X With a 255.255.255.252 maskOr /30 the 1 subnet
my be broken into 64 Subnets
161616© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Administrative Distance• The router treats different routing protocols with a different preference
Route SourceRoute Source Default DistanceDefault Distance
Connected InterfaceConnected Interface
Static RouteStatic Route
Enhanced IGRP Summary RouteEnhanced IGRP Summary Route
External BGPExternal BGP
Internal Enhanced IGRPInternal Enhanced IGRP
IGRPIGRP
OSPFOSPF
IS-ISIS-IS
RIPRIP
EGPEGP
External Enhanced IGRPExternal Enhanced IGRP
Internal BGPInternal BGP
Unknown, Discard RouteUnknown, Discard Route
00
11
55
2020
9090
100100
110110
115115
120120
140140
170170
200200
255255
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
17© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF
181818© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF
• Open ShortestPath First
• Link state or SPF technology
• Developed by OSPF working group of IETF (RFC 1247)
• Designed for TCP/IP Internet environment
• Fast convergence
• Variable-length subnet masks
• Discontiguoussubnets
• No periodic updates
• Route authentication
• Delivered two years after IGRP
• OSPF standard described in RFC2328
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
191919© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Link State
Topology Information Is Kept in a Database Separate from the
Routing Table
AABBCC
2213131313
QQZZXX
X’s Link State
ZZ
XX
YYQQ
Z’s Link State
Q’s Link State
202020© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Link-State
TopologicalDatabase
2 SPF
Algorithm
3 Shortest Path First Tree
4
Routing Table
5
Link-State Advertisements C
1 DA
B
C
D
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
212121© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Why Is It Called a Link State Protocol?
• Traditional Distance Vector Routing Protocols (DVRP) relay information regarding their relative distance to a destination
• Link State Protocols relay specific link characteristics and state information
• Only changes or updates are sent across the network
• Each router uses that information to build a routing table on it’s own
222222© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Link-State vs. Distance Vector Protocols
• Link-State router tells ALL other routers about ONLY its neighbors and links
• Distance Vector router tells ONLY neighbors about ALL routes
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
232323© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
What Is a Link State Protocol ?
• The network can be viewed as a “ jigsaw puzzle”
• Each piece of the puzzle holds one router
• Each router creates a Link State Packet (LSP) which represents its own jigsaw piece
• LSPs are flooded reliably within the network
• The LSPs are collected by each router to form a Link State Database (LSDB) or complete “ picture” of the network
• Use Shortest Path First (SPF) algorithm to put the pieces together
242424© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
LSP ALSP B
LSP C
LSP D
to B
to EtoDto C
to A
to Dto C
to B
LSP E
to A to B
to A
to E
Link State Protocols
to C to D
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
252525© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
All Routers Have the Same View
• All routers exchange all LSPs
Via a reliable flooding mechanism
• All routers store all LSPs in a link-state database (LSDB)
Separate from the routing table (RIB)
All routers should have exactly the same LSDB, but different RIBs
262626© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Router A - LSDBRouter B - LSDB
Router D - LSDBRouter C - LSDB
Router E - LSDBLSPE
LSPE
LSPELSPE
LSPE
LSPA
LSPA
LSPALSPA
LSPALSPC
LSPC
LSPCLSPC
LSPC
LSPB
LSPB
LSPBLSPB
LSPBLSPD
LSPD
LSPDLSPD
LSPD
All Routers Have the Same LSDB
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
272727© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Link State Routing
• Neighbour discovery
• Constructing an LSP
• Distribute LSP
• Compute routes
• On network failureNew LSPs flooded
All routers recompute routing tables
282828© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
What To Do With LSPs?
• Each router calculates a topology map by executing Dijkstra’s Shortest Path First algorithm (SPF)
the topology is calculated as a Shortest Path Tree (SPT), with itself as root
each router computes a different Shortest Path Tree (SPT)
• From the SPT the RIBs are calculated
RIB : Routing Information Base
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
292929© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
• Dijkstra is a path finding algorithm
• Will find the shortest path from A to B given intermediate path and cost information
• One of many path finding algorithms:
Dijkstra, best path, A*, etc
Dijkstra
Shortest Path First (SPF) Algorithm
303030© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Dijkstra’s algorithm
• ������������������������������������������������ � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � ����� �� �� �� � � �� �� �� � � � � �� ! �� � � �� ! �� � � �� ! �� � � �� ! � � � � � �� � � � �� � � � �� � � � � �� " # � � ��� " # � � ��� " # � � ��� " # � � �� $ % �& ' ! (� $ % �& ' ! (� $ % �& ' ! (� $ % �& ' ! (
• ����) �* + $ % & ' ! �, - . / ! * 0�1 � ") �* + $ % & ' ! �, - . / ! * 0�1 � ") �* + $ % & ' ! �, - . / ! * 0�1 � ") �* + $ % & ' ! �, - . / ! * 0�1 � "2 3 4 5 62 3 4 5 62 3 4 5 62 3 4 5 6 � � � � �� � � � �� � � � �� � � � � 07 8 9 * + ! �: ; (07 8 9 * + ! �: ; (07 8 9 * + ! �: ; (07 8 9 * + ! �: ; (
• �< �6 $ % = > ? ��1 @ 5 ���A �(�< �6 $ % = > ? ��1 @ 5 ���A �(�< �6 $ % = > ? ��1 @ 5 ���A �(�< �6 $ % = > ? ��1 @ 5 ���A �(B � ���C D ! EB � ���C D ! EB � ���C D ! EB � ���C D ! E F �F �F �F � � G � ��H I 6� G � ��H I 6� G � ��H I 6� G � ��H I 6 J �J �J �J � 0000F �F �F �F � ���( , � K L M ��1 N O C D E���( , � K L M ��1 N O C D E���( , � K L M ��1 N O C D E���( , � K L M ��1 N O C D E F �F �F �F � ����! � P Q R @ (! � P Q R @ (! � P Q R @ (! � P Q R @ (
• �S ���S ���S ���S �� F �F �F �F � � � $ % �& ' ! � T U V W ) X < X� � $ % �& ' ! � T U V W ) X < X� � $ % �& ' ! � T U V W ) X < X� � $ % �& ' ! � T U V W ) X < XS ( Y Z [ 0= \ @ 5 ����! ] P Q # �S ( Y Z [ 0= \ @ 5 ����! ] P Q # �S ( Y Z [ 0= \ @ 5 ����! ] P Q # �S ( Y Z [ 0= \ @ 5 ����! ] P Q # �! R * + �1 (! R * + �1 (! R * + �1 (! R * + �1 (
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
313131© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Dijkstra
• Link state databaseCreated with link state packets (LSPs) from each router
• TENT databaseTentative triples (ID, path cost, direction)
Shortest Path First (SPF) Algorithm
323232© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Dijkstra (SPF) Overview
• PATH database
Best path triples (ID, path cost, direction)
• Forwarding database
Aka the routing table
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
333333© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Dijkstra (SPF) Overview (Cont.)
• All routers exchange Link State Packets (LSPs)
• Each starts with itself as root
• Tent is built from LSPs
• Path is created by examining and comparing tent triples
• Once path is final the forwarding table is populated
343434© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Dijkstra Basics
• Router IDs are alphabetic
• Costs are numeric
• Lowest cost best
B B A A C C
D D
E E F F G G
4
2
2 2
2
1 4
1
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
353535© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
LSP Data
B B A A C C
D D
E E F F G G
4
2
2 2
2
1 4
1
BB CC DD EE FF
B/4B/4
GG
A/4A/4
AA
B/1B/1 C/4C/4 C/2C/2 E/2E/2 A/2A/2
G/2G/2 C/1C/1 D/4D/4
E/2E/2
E/1E/1 D/1D/1
F/2F/2
G/2G/2 F/2F/2
363636© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Dijkstra Example—1/7
• As an example start with B
• A and C costs are tent
B B
A A C C
(0)
(1) (4)
BB CC DD EE FF
B/4B/4
GG
A/4A/4
AA
B/1B/1 C/4C/4 C/2C/2 E/2E/2 A/2A/2
G/2G/2 C/1C/1 B/1B/1
E/2E/2
E/1E/1 D/1D/1
F/2F/2
G/2G/2 F/2F/2
BB CC DD EE FF
B/4B/4
GG
A/4A/4
AA
B/1B/1 C/4C/4 C/2C/2 E/2E/2 A/2A/2
G/2G/2 C/1C/1 D/4D/4
E/2E/2
E/1E/1 D/1D/1
F/2F/2
G/2G/2 F/2F/2
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
373737© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Dijkstra Example—2/7
• Now fill in C• D,E are in tent• BC is now in path
B B
A A C C
(0)
(1) (4)
D D
E E (5)
(3)
BB CC DD EE FF
B/4B/4
GG
A/4A/4
AA
B/1B/1 C/4C/4 C/2C/2 E/2E/2 A/2A/2
G/2G/2 C/1C/1 D/4D/4
E/2E/2
E/1E/1 D/1D/1
F/2F/2
G/2G/2 F/2F/2
383838© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
• Now fill in C• D,E are in tent• BC is now in path
A A (4)
Dijkstra Example—3/7
B B
C C
(0)
(1)
D D
E E (5),(4)
(3) F F (5)
BB CC DD EE FF
B/4B/4
GG
A/4A/4
AA
B/1B/1 C/4C/4 C/2C/2 E/2E/2 A/2A/2
G/2G/2 C/1C/1 D/4D/4
E/2E/2
E/1E/1 D/1D/1
F/2F/2
G/2G/2 F/2F/2
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
393939© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
A A (4)
• Now fill in A• G is in tent• BA is now in path
Dijkstra Example—4/7
B B
C C
(0)
(1)
D D
E E (5),(4)
(3) G G
(6) F F (5)
BB CC DD EE FF
B/4B/4
GG
A/4A/4
AA
B/1B/1 C/4C/4 C/2C/2 E/2E/2 A/2A/2
G/2G/2 C/1C/1 D/4D/4
E/2E/2
E/1E/1 D/1D/1
F/2F/2
G/2G/2 F/2F/2
404040© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
A A (4)
Dijkstra Example—5/7
• CD is removed• ED is placed in path
B B
C C
(0)
(1)
D D
E E (4)
(3) G G
(6) F F (5)
BB CC DD EE FF
B/4B/4
GG
A/4A/4
AA
B/1B/1 C/4C/4 C/2C/2 E/2E/2 A/2A/2
G/2G/2 C/1C/1 D/4D/4
E/2E/2
E/1E/1 D/1D/1
F/2F/2
G/2G/2 F/2F/2
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
414141© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
A A (4)
Dijkstra Example—6/7
• Now fill in F• G is Tent• GF does not
provide better path • EF is in path
B B
C C
(0)
(1)
D D
E E (4)
(3) G G
(6) F F (5),(8)
BB CC DD EE FF
B/4B/4
GG
A/4A/4
AA
B/1B/1 C/4C/4 C/2C/2 E/2E/2 A/2A/2
G/2G/2 C/1C/1 D/4D/4
E/2E/2
E/1E/1 D/1D/1
F/2F/2
G/2G/2 F/2F/2
424242© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
A A (4)
Dijkstra Example—7/7
• Now fill in G• FG is removed• AG is in path
B B
C C
(0)
(1)
D D
E E (4)
(3) G G
(6) F F (5)
BB CC DD EE FF
B/4B/4
GG
A/4A/4
AA
B/1B/1 C/4C/4 C/2C/2 E/2E/2 A/2A/2
G/2G/2 C/1C/1 D/4D/4
E/2E/2
E/1E/1 D/1D/1
F/2F/2
G/2G/2 F/2F/2
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
434343© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Autonomous System
OSPF Terminology
RoutingTable
Lists Best Routes
Topology Database
Lists All Routes
Neighborship Database
Lists Neighbors
Cost = 10
Cost = 1785 Cost = 6
Neighbors
TokenRing
Interfaces
Area 1Area 0
444444© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF Topologies
Point-to-Point
NBMA
Broadcast Multiaccess
X.25Frame Relay
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
454545© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
FDDI Dual Ring
FDDI Dual Ring
Optimal Path Utilisation
N1
N2 N3
N4
N5R1
R2
R3
R4
Cost = 1 Cost = 1
Cost = 10
Cost = 10
The optimal path is determined by thesum of the interface costs: Cost = 10^8/BW
464646© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Fast Convergence
• Detection Plus LSA/SPF
XR1 R3
R2
N2
Primary Path
N1
Alternate Path
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
474747© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Fast Convergence
• Finding a new route
LSA flooded throughout area
Acknowledgement based
Topology database synchronised
Each router derives routing table to destination networks
LSA
XR1
N1
484848© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
FDDIDual Ring
Low Bandwidth Utilisation
• Only changes propagated
• Multicast on multi-access broadcast networks
R1
LSA
XLSA
LSA : Link State Advertisement
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
494949© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Utilises IP Multicast for Sending/Receiving Updates
• Broadcast networksDR and BDR —> AllSPFRouters (224.0.0.5)
All other routers —> AllDRRouters (224.0.0.6)
• Hello packets sent to AllSPFRouters(Unicast on point-to-point and virtual links)
505050© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF Areas
• Group of contiguous hosts and networks
• Per area topological database
Invisible outside the area
Reduction in routing traffic
• Backbone area contiguous
All other areas must be connected to the backbone
• Virtual Links Area 1Area 4
Area 0Backbone Area
Area 2 Area 3
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
515151© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Classification of Routers
• Internal Router (IR)
• Area Border Router (ABR)
• Backbone Router (BR)
• Autonomous System Border Router (ASBR)
Area 1
IRArea 0
Area 2 Area 3
IR
ABR
To other AS
ASBR
/BR
/BR
525252© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF Route Types
Intra-area Route “ O”all routes inside an area
Inter-area Route “ O IA”routes advertised from one area to another by an Area Border Router
External Route “ O E1” or “ O E2”routes imported into OSPF from other protocol or static routes
Area 0Area 2 Area 3
ABR
To other AS
ASBR
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
535353© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Inter-Area Route Summarisation
• Prefix or all subnets
• Prefix or all networks
• ‘Area range’ command
1.A 1.B 1.C
FDDIDual Ring
R1 (ABR)
R2
Network1
Next HopR1
Network1.A1.B1.C
Next HopR1R1R1
With summarisation
Withoutsummarisation
BackboneArea 0
Area 1
545454© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
External Routes
• Redistributed into OSPF
• Flooded unaltered throughout the AS
• OSPF supports two types of external metricsType 1 external metrics
Type 2 external metrics (Default)
RIPIGRPEIGRPBGPetc.
OSPF
Redistribute
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
555555© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
External Routes
• Type 1 external metric: metrics are added to the summarised internal link cost
NetworkN1N1
Type 11110
Next HopR2R3
Cost = 10
to N1External Cost = 1
to N1External Cost = 2R2
R3
R1
Cost = 8
Selected Route
565656© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
External Routes
• Type 2 external metric: metrics are compared without adding to the internal link cost
NetworkN1N1
Type 212
Next HopR2R3
Cost = 10
to N1External Cost = 1
to N1External Cost = 2R2
R3
R1
Cost = 8
Selected Route
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
575757© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Topology/Link State Database
• A router has a separate LS database for each area to which it belongs
• All routers belonging to the same area have identical database
• SPF calculation is performed separately for each area
• LSA flooding is bounded by area
585858© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Protocol Functionality
• Bringing up adjacencies
• LSA types
• Area classification
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
595959© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
The Hello Protocol
• Responsible for establishing and maintaining neighbour relationships
• Elects designated router on multi-access networks
FDDIDual Ring
Hello
HelloHello
606060© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Neighborship
Hello
afadjfjorqpoeru39547439070713
Router IDHello/dead intervalsNeighborsArea-IDRouter priorityDR IP addressBDR IP addressAuthentication passwordStub area flag
* *
**
* Entry must match on neighboring routers
Hello
AA
DD EE
CCBB
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
616161© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Neighborship (cont.)
Hello
afadjfjorqpoeru39547439070713
Router IDHello/dead intervalsNeighborsArea-IDRouter priorityDR IP addressBDR IP addressAuthentication passwordStub area flag
**
**
* Entry must match on neighboring routers
Hello
AA
DD EE
CCBB
626262© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
DR and BDR
DRDR BDRBDR
Hellos elect DR and BDR to represent segment
Each router then forms adjacency with DR and BDR
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
636363© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Designated Router
• One per multi-access networkGenerates network links advertisements
Assists in database synchronization
Designated Router
Designated Router
BackupDesignated Router
BackupDesignated
Router
646464© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Designated Router by Priority
• Configured priority (per interface)
• Else determined by highest router ID
Router ID is the loopback interface address, if configured, otherwise the highest IP address
144.254.3.5
R2 Router ID = 131.108.3.3
131.108.3.2 131.108.3.3
R1 Router ID = 144.254.3.5
DR
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
656565© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
When to Become Adjacent
• Underlying network is point to point
• Underlying network type is virtual link
• The router itself is the designated router
• The router itself is the backup designated router
• The neighbouring router is the designated router
• The neighbouring router is the backup designated router
666666© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Building the Adjacency
1- Down: No information has been received from anybody on the segment.2- Init: The interface has detected a Hello packet coming from a neighbor but bi-directional communication has not yet been established.3- Two-way: There is bi-directional communication with a neighbor. The router has seen itself in the Hello packets coming from a neighbor. At the end of this stage the DR and BDR election would have been done. At the end of the 2way stage, routers will decide whether to proceed inbuilding an adjacency or not. The decision is based on whether one of the routers is a DR or BDR or the link is a point-to-point or a virtual link.4- Exstart: Routers are trying to establish the initial sequence number that is going to be used in the information exchange packets. The sequence number insures that routers always get the most recent information. One router will become the primary and the other will become secondary. The primary router will poll the secondary for information.5- Exchange: Routers will describe their entire link-state database by sending database description packets. At this state, packets could be flooded to other interfaces on the router.6- Loading: At this state, routers are finalizing the information exchange. Routers have built a link-state request list and a link-state retransmission list. Any information that looks incompleteor outdated will be put on the request list. Any update that is sent will be put on the retransmission list until it gets acknowledged.7- Full: At this state, the adjacency is complete. The neighboring routers are fully adjacent. Adjacent routers will have a similar link-state database.
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
676767© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Neighbor and Adjacency
RTD# show ip ospf interface e 0Ethernet0 is up, line protocol is upInternet Address 203.250.14.4 255.255.255.0, Area 0.0.0.0Process ID 10, Router ID 192.208.10.174, Network Type BROADCAST, Cost: 10Transmit Delay is 1 sec, State DROTHER, Priority 1Designated Router (ID) 203.250.15.1, Interface address 203.250.14.2Backup Designated router (ID) 203.250.13.41, Interface address 203.250.14.1Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 0:00:03Neighbor Count is 3, Adjacent neighbor count is 2Adjacent with neighbor 203.250.15.1 (Designated Router)Adjacent with neighbor 203.250.13.41 (Backup Designated Router)
RTD# show ip ospf neighborNeighbor ID Pri State Dead Time Address Interface203.250.12.1 1 2WAY/DROTHER 0:00:37 203.250.14.3 Ethernet0203.250.15.1 1 FULL/DR 0:00:36 203.250.14.2 Ethernet0203.250.13.41 1 FULL/BDR 0:00:34 203.250.14.1 Ethernet0
686868© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Routing Protocol Packets
• Share a common protocol header
• Routing protocol packets are sent with type of service (TOS) of 0
• Five types of OSPF routing protocol packets
Hello - packet type 1
Database description - packet type 2
Link-state request - packet type 3
Link-state update - packet type 4
Link-state acknowledgement - packet type 5
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
696969© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Different Types of LSAs
• Five distinct type of LSAs
Type 1 : Router LSA
Type 2 : Network LSA
Type 3 and 4: Summary LSA
Type 5 and 7: External LSA
707070© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Router LSA (Type 1)
• Describes the state and cost of the router’s links to the area
• All of the router’s links in an area must be described in a single LSA
• Flooded throughout the particular area and no more
• Router indicates whether it is an ASBR, ABR, or end point of virtual link
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
717171© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Network LSA (Type 2)
• Generated for every transit broadcast and NBMA network
• Describes all the routers attached to the network
• Only the designated router originates this LSA
• Flooded throughout the area and no more
NBMA : Non-Broadcast Multi-Access
727272© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Summary LSA (Type 3 and 4)
• Describes the destination outside the area but still in the AS
• Flooded throughout a single area
• Originated by an ABR
• Only intra-area routes are advertised into the backbone
• Type 4 is the information about the ASBR
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
737373© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
External LSA (Type 5)
• Defines routes to destination external to the AS
• Default route is also sent as external
• Two types of external LSA:E1: Consider the total cost up to the external destination
E2: Considers only the cost of the outgoing interface to the external destination
747474© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Not Summarised: Specific Links
BackboneArea #0
External links
1.A
1.C
1.B
1.D
TokenRing
TokenRing
TokenRing
TokenRing
3.D
3.A
3.C
3.B
1.A1.B1.C1.D
3.A3.B3.C3.D
2.A2.B2.C
2.A
2.C
2.B
TokenRing
TokenRing
• Specific link LSA advertised out• Link state changes propagate out
ASBR
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
757575© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
BackboneArea #0
External links
1.A
1.C
1.B
1.D
TokenRing
TokenRing
TokenRing
TokenRing
3.D
3.A
3.C
3.B
2.A
2.C
2.B
TokenRing
TokenRing
ASBR
Not Summarised: Specific Links
2.A2.B2.C3.A3.B3.C3.D
1.A1.B1.C1.D3.A3.B3.C3.D
1.A1.B1.C1.D2.A2.B2.C
• Specific link LSA advertised in• Link state changes propagate in
767676© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Summarised: Summary Links
BackboneArea #0
ASBR
External links
1.A
1.C
1.B
1.D
TokenRing
TokenRing
TokenRing
TokenRing
3.D
3.A
3.C
3.B
2.A
2.B
TokenRing
TokenRing
• Only summary LSA advertised out• Link state changes do not propagate
1 3
2
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
777777© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Summarised: Summary Links
BackboneArea #0
3.D
3.A
2.B
• Only summary LSA advertised in• Link state changes do not propagate
ASBR
External links
1.A
1.C
1.B
1.D
TokenRing
TokenRing
TokenRing
TokenRing
3.C
3.B
2.A
TokenRing
TokenRing
2,3
1,3
1,2
787878© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Addressing
Area 1network 131.108.0.0subnets 17-31range 255.255.240.0
Area 2network 131.108.0.0subnets 33-47range 255.255.240.0
Area 3network 131.108.0.0subnets 49-63range 255.255.240.0
Area 0network 192.117.49.0range 255.255.255.0
Assign contiguous ranges of subnets per area to facilitate summarisation
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
797979© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
TokenRing
TokenRing
TokenRing
TokenRing
Regular Area
From area 1’s viewpoint • Summary networks from other areas injected• External networks injected, for example network X.1
ASBR
External Networks
1.A
1.C
1.B
1.DTokenRing
TokenRing
3.C
3.B
2.A
2,3
1,3
1,2X.1
X.1
X.1
X.1
2.D2.C
2.B
3.A
3.D
808080© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
TokenRing
TokenRing
TokenRing
TokenRing
Normal Stub Area
From area 1’s viewpoint
• Summary networks from other areas injected
• Default network injected into the area - represents external links
• Default path to closest area border router
• Define all routers in the area as stub
area x stub command
ASBR
External Networks
1.A
1.C
1.B
1.DTokenRing
TokenRing
3.C
3.B
2.A
& Default
1,3
1,2X.1
X.1
X.1
X.1
2.D2.C
2.B
3.A
3.D
2,3
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
818181© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
TokenRing
TokenRing
TokenRing
TokenRing
Totally Stubby Area
From area 1’s viewpoint
• Only a default network is injected into the areaRepresents external networks and all inter-area routes
• Default path to closest area border router
• Define all routers in the area as totally stubby area x stub no-summary command
ASBR
External Networks
1.A
1.C
1.B
1.DTokenRing
TokenRing
3.C
3.B
2.A
2, 3 & Default
1,3
1,2X.1
X.1
X.1
X.1
2.D2.C
2.B
3.A
3.D
Default
828282© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
TokenRing
TokenRing
TokenRing
TokenRing
Not-So-Stubby Area
• Capable of importing external routes in a limited fashion
• Type-7 LSA’s carry external information within an NSSA
• NSSA Border routers translate selected type-7 LSAs into type-5 external network LSAs
ASBR
External Networks
1.A
1.C
1.B
1.DTokenRing
TokenRing
3.C
3.B
2.A
Default
1,3
1,2X.1
X.1
X.1X.1
2.D2.C
2.B
3.A
3.DExternal Networks
X.2
X1, X2
X1, X2
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
838383© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Area 0.0.0.0
Area 0.0.0.1
Area 0.0.0.4
Virtual Link
Area 0.0.0.3 Area 0.0.0.5
VirtualLink
Virtual Links
Area 0.0.0.6
848484© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Area 0
Area 1
Area 2
Area3
Virtual Links
XXXXVirtual Link
Virtual LinkRouter A (RID 171.0.1.7)
router ospf 100area 2 virtual-link 171.0.1.5
Router B (RID 171.0.1.5)router ospf 100
area 2 virtual-link 171.0.1.7
Router A
Router B
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
858585© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Summary
• Scalable OSPF Network Design
Area hierarchy
Stub areas
Contiguous addressing
Route summarisation
86© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Reference Commands
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
878787© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF - Adding Networks(Method One)
• redistribute connected subnets
Works for all connected interfaces on the router but sends networks as external type-2s -which are not summarizedrouter ospf 100
redistribute connected subnets
• Not recommended
888888© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF - Adding Networks
• Specific network statements
Every interface needs a OSPF network statement. Interface that should not be broadcasting OSPF Hello packets needspassive-interface.router ospf 100
network 192.168.1.4 0.0.0.3 area 51
network 192.168.1.6 0.0.0.3 area 51
passive interface Serial 1/0
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
898989© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF - Adding Networks
• Network statements - wildcard mask
Every interface covered by wildcard mask used in OSPF network statement. Interfaces that should not be broadcasting OSPF Hello packets need passive-interface or default passive-interface. router ospf 100
network 192.168.1.0 0.0.0.255 area 51
default passive-interface default
no passive interface POS 4/0
909090© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF - Adding Networks
• Key Theme when selecting a technique: Keep the Link State Database Lean
Increases Stability
Reduces the amount of information in the Link State Advertisements (LSAs)
Speeds Convergence Time
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
919191© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF Logging Neighbour Changes
• The router will generate a log messagewhenever an OSPF neighbour changes state
• Syntax:[no] ospf log[no] ospf log--adjacencyadjacency--changeschanges
• Example of a typical log message:%OSPF%OSPF--55--ADJCHG: Process 1, ADJCHG: Process 1, NbrNbr 223.127.255.223 on 223.127.255.223 on Ethernet0 from LOADING to FULL, Loading DoneEthernet0 from LOADING to FULL, Loading Done
929292© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Number of State Changes
• The number of state transitions is available via SNMP (ospfNbrEvents) and the CLI:
show ip ospf neighbor [type number] show ip ospf neighbor [type number] [neighbor[neighbor--id] [detail]id] [detail]
Detail—(Optional) Displays all neighbours given in detail (list all neighbours). When specified, neighbour state transition counters are displayed per interface or neighbour ID
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
939393© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
State Changes (Continued)
• To reset OSPF-related statistics, use the clear ip ospf countersclear ip ospf counters EXEC command. At this point neighborneighbor is the only available option; it will reset neighbour state transition counters per interface or neighbour id
clear ip ospf counters [neighbor [<type clear ip ospf counters [neighbor [<type number>] [neighbornumber>] [neighbor--id]]id]]
949494© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF Router ID
• If the loopback interface exists and has an IP address, that is used as the router ID in routing protocols - stability!
• If the loopback interface does not exist, or has no IP address, the router ID is the highest IP address configured - danger!
• New sub command to manually set the OSPF Router ID:
router-id <ip address>
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
959595© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF Clear/Restart
• clear ip ospf [pid] redistributionThis command can now clear redistribution based on OSPF routing process ID. If no pid is given, it assumes all OSPF processes.
• clear ip ospf [pid] countersThis command can now clear counters based on OSPF routing process ID. If no pid is given, it assumes all OSPF processes.
• clear ip ospf [pid] processThis command will restart the specified OSPF process. If no pid is given, it assumes all OSPF processes. It attempts to keep the old router-id, except in cases, where a new router-id was configured, or an old user configured router-id was removed. Since this command can potentially cause a network churn, a user confirmation is required before performing any action.
969696© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Redistributing Routes into OSPF
ROUTER OSPF <pid#x>
REDISTRIBUTE {protocol} <as#y>
<metric>
<metric-type (1 or 2)
<tag>
<subnets>
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
979797© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Router Sub-commands
• NETWORK <n.n.n.n> <mask> AREA <area-id>
• AREA <area-id> STUB {no-summary}
• AREA <area-id> AUTHENTICATION
• AREA <area-id> VIRTUAL-LINK <router-id>...
• AREA <area-id> RANGE <address mask>
989898© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Interface Subcommands
• IP OSPF COST <cost>
• IP OSPF PRIORITY <8-bit-number>
• IP OSPF HELLO-INTERVAL <number-of-seconds>
• IP OSPF DEAD-INTERVAL <number-of-seconds>
• IP OSPF AUTHENTICATION-KEY <8-bytes-of-password>
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
999999© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Router#
show ip ospf interface
Verifying OSPF Operation
• Displays area ID and adjacency information
Router#
show ip protocols
• Verifies that OSPF is configuredRouter#
show ip route
• Displays all the routes learned by the router
100100100© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
• Displays OSPF timers and statistics
• Displays information about DR, BDR, and neighbors
• Displays the link-state database
Verifying OSPF Operation (cont.)
Router#
show ip ospf neighbor detail
Router#
show ip ospf database
Router#
show ip ospf
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
101101101© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
• Allows you to clear the IP routing table
Router#
clear ip route *
Router#
debug ip ospf option
• Displays router interaction during the hello, exchange, and flooding processes
Verifying OSPF Operation (cont.)
102102102© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
Configuring OSPF ABRs
E010.64.0.1
10.64.0.2E0
S010.2.1.2
10. 2.1.1S1AA BB CC
ABR
<Output Omitted>
interface Ethernet0
ip address 10.64.0.1 255.255.255.0
!
<Output Omitted>
router ospf 77
network 10.0.0.0 0.255.255.255 area 0
Area 1Area 0
<Output Omitted>
interface Ethernet0
ip address 10.64.0.2 255.255.255.0
!
interface Serial0
ip address 10.2.1.2 255.255.255.0
<Output Omitted>
router ospf 50
network 10.2.1.2 0.0.0.0 area 1
network 10.64.0.2 0.0.0.0 area 0
Copyright © 2000, Cisco Systems, Inc. All rights reserved. Printed in USA.Presentation_ID.scr
103103103© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2
OSPF Stub Area Configuration Example
192.168.15.2
Area 0
Stub Area 2
192.168.14.1 192.168.15.1S0
S0E0
R3#
interface Ethernet 0ip address 192.168.14.1 255.255.255.0interface Serial 0 ip address 192.168.15.1 255.255.255.252
router ospf 100network 192.168.14.0 0.0.0.255 area 0network 192.168.15.0 0.0.0.255 area 2area 2 stub
R4#
interface Serial 0 ip address 192.168.15.2 255.255.255.252
router ospf 15network 192.168.15.0 0.0.0.255 area 2area 2 stub
ExternalAS
R4R4
R3R3
104104104© 2003, Cisco Systems, Inc. All rights reserved.
RST-10018118_05_2003_c2 104