© synergon informatika rt., 1999 chapter 9 configuring open shortest path first
TRANSCRIPT
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© Synergon Informatika Rt., 1999
Synergon Informatika Rt.
Chapter 9
Configuring Open Shortest Path First
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Objectives
Upon completion of this chapter, you will be able to perform the following tasks:
Describe OSPF features and operation
Configure OSPF for proper operation
Use Cisco IOS summarization and stub-area features for OSPF
Verify OSPF operation
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OSPF Features and Operation
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OSPF Overview
Standard IP link-state routing protocol
Designed to overcome RIP limitations
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OSPF Features
Has no hop count limitation
Supports VLSM
Uses multicast addressing for updates
Has faster convergence
Allows for routing authentication
Supports hierarchical routing
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OSPF Hierarchical Routing
Consist of areas and autonomous systems
Minimizes routing update traffic
Area 0
Area 1 Area 2
Autonomous System
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OSPF Router Types
Area 1 Backbone Area 0 Area 2
External AS
Area Border Router
AS Boundary Router
Internal Router
Backbone Router
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The Backbone and Virtual Links
Backbone center of communication
Virtual links provide path to backbone
Avoid configuring virtual links if possible
Virtual LinkArea 0
(Backbone)
Area 1 Area 2
Area 3
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Another Use for Virtual Links
Link discontinuous backbone
- Merged networks
- Redundancy
Area 3Area 0Area 0
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The Link-State Database
Represents the network topology
Shared with OSPF routers in same area
Adjacent
Link-State Database Link-State Database
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Link-State Advertisements (LSAs)
Sourced by router connected to link
Flooded by all other routers in area
Transmitted at each link-state change
LSA
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Link-State Advertisement Operation
LSA LSA
LSA
LSA received
Add to database
Flood LSA
Run SPF to calculate new table
Reset timer for entryYes
No
Is entry in topological database?
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Types of Link-State Packets
O — OSPF Derived Intra-Area (Router LSA)IA — Inter-Area (Summary LSA)E1 — Type 1 External RouteE2 — Type 2 External Route
Routing Table ExternalAS
ASBR
DRArea 1 Area 0
ABR
Network
Router
External
Summary
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Types of External Routes
Type-1 (E1) metric — external + internal
Type-2 (E2) metric — external cost only
5 5
Area 1 Area 0
R1R2R3
N1 cost = 30N2 cost = 20
N1 cost = 25N2 cost = 20
Cost = 20
20N2(E2)
N1(E1)
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OSPF Network Types
Point-to-Point
BroadcastMultiaccess
X.25Frame Relay
NonbroadcastMultiaccess
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OSPF Router ID
Number by which the router is known to OSPF
- Default: The highest IP address on an active interface
- Can be overridden by a loopback interface
Network131.108.0.0
Bogus Loopback AddressEx: 1.1.1.1• Not in OSPF table• Saves address space
Bogus Loopback AddressEx: 1.1.1.1• Not in OSPF table• Saves address space
Real Loopback AddressEx: 131.108.17.5• In OSPF table• Uses address space
Real Loopback AddressEx: 131.108.17.5• In OSPF table• Uses address space
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Neighbors
Form using the Hello protocol
Hello
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Adjacencies
Hellos elect designated router (DR) and backup designated
router (BRD)
Each router forms adjacency with DR and BDR
DR BDR
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Designated Router Election
Hello packets exchanged via IP multicast
Router with highest OSPF priority elected
Hello
DR BDR
P=3 P=2
P=1 P=1 P=0
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Multiaccess Network
New router announces presence
DR and BDR respond
Adding a Router
NewRouter
DR
BDR224.0.0.5 Hello
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Multiaccess Network (cont.)
New router sends LSAs to DR and BDR
BDR waits for DR to respond
Adding a Router
New Router
DR
BDR224.0.0.6 LSA
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Multiaccess Network (cont.)
DR transmits LSAs to other routers
DR must receive ACK from all routers
Adding a Router
New Router
DR
BDR
224.0.0.5 LSA
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Multiaccess Network (cont.)
Source router tells DR on 224.0.0.6
DR tells others on 224.0.0.5
Other routers flood LSAs
Link-State Change
New Router
DR
BDR
XX
LSA
LSA
LSA
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Configuring OSPF
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OSPF Basic Configuration Commands
Router (config) #
router ospf process-idrouter ospf process-id
Enables on OSPF routing process
Router (config-router ) #
network address wildcard-mask area area-idnetwork address wildcard-mask area area-id
• Selects participating interfaces
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OSPF Basic Configuration Example
TokenRing
router ospf 63network 172.16.5.3 0.0.0.0 area 1network 172.16.0.0 0.0.255.255 area 0network 192.168.10.5 0.0.0.0 area 1
router ospf 63network 172.16.5.3 0.0.0.0 area 1network 172.16.0.0 0.0.255.255 area 0network 192.168.10.5 0.0.0.0 area 1
172.16.5.3
192.168.10.5172.16.1.1
172.16.3.1
T0
E0E1
E2
Area 1
Area 0
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OSPF Virtual Link Command
Router (config-router) #
Area area-id virtual-link router-idArea area-id virtual-link router-id
Creates a virtual link
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OSPF Virtual Link Example
TokenRing
R2:router ospf 63area 1 virtual-link 192.168.10.5
R2:router ospf 63area 1 virtual-link 192.168.10.5
Area 1
Area 0
Area 3
Router ID 192.168.10.5
Router ID 192.168.20.123
R1:router ospf 100area 1 virtual-link 192.168.20.123
R1:router ospf 100area 1 virtual-link 192.168.20.123
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Vendor Interoperability
TokenRing
• Assigns a cost to an outgoing interface
• May be required for interoperability
• Use default cost between Cisco devices
Traffic
Non-CiscoCisco
Router (config-if ) #
Ip ospf cost costIp ospf cost cost
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Using Route Summarization, Stub Areas, and Redistribution
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OSPF Route Summarization
X
• Minimizes routing table entries
• Localizes impact of a topology change
Area 1
ABRs
Summarization
Area 0 Backbone
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Route Summarization (cont.)
• Interarea (IA) summary link carries mask
• One entry can represent several subnet
Area 1 Area 0ABR
Summarization
O 131.108.4.0 255.255.255.0O 131.108.8.0 255.255.255.0O 131.108.12.0 255.255.255.0O 131.108.16.0 255.255.255.0O 131.108.20.0 255.255.255.0O 131.108.24.0 255.255.255.0O 131.108.28.0 255.255.255.0
IA 131.108.16.0 255.255.240.0
Routing Table for C
Routing Table for B
A B C
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Route Summarization Issue
Existing Subnet
Mask = 252 1111 11 00 Valid
131.108.12.0 255.255.255.0 Address = 12 0000 11 00 3rd Subnet
Summary Route
Mask = 240 1111 0000 Invalid Subnet
131.108.12.0 255.255.240.0 Address = 12 0000 1100 zero
• Some addresses may need reallocating
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Route Summarization Commands
Router (config-router ) #
Area area-id range address maskArea area-id range address mask
Consolidates IA router on an ABR
Router (config-router ) #
Summary-address address maskSummary-address address mask
• Consolidates external routes on an ASBR
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Route Summarization ExampleArea 0
Area 1 Area 2
172.16.96.0 - 172.16.127.0 255.255.255.0
172.16.64.0 - 172.16.95.0 255.255.255.0
172.16.32.0 - 172.16.63.0 255.255.255.0
172.16.32.1 172.16.64.1
172.16.127.1172.16.96.1
Interface Addresses
(255.255.255.0 mask)Interface Addresses
(255.255.255.0 mask)
R1#router ospf 100network 172.16.32.0 0.0.31.255 area 1network 172.16.96.0 0.0.31.255 area 0area 0 range 172.16.96.0 255.255.224.0area 1 range 172.16.32.0 255.255.224.0
R1#router ospf 100network 172.16.32.0 0.0.31.255 area 1network 172.16.96.0 0.0.31.255 area 0area 0 range 172.16.96.0 255.255.224.0area 1 range 172.16.32.0 255.255.224.0
R2#router ospf 100network 172.16.32.0 0.0.31.255 area 2network 172.16.96.0 0.0.31.255 area 0area 0 range 172.16.96.0 255.255.224.0area 2 range 172.16.64.0 255.255.224.0
R2#router ospf 100network 172.16.32.0 0.0.31.255 area 2network 172.16.96.0 0.0.31.255 area 0area 0 range 172.16.96.0 255.255.224.0area 2 range 172.16.64.0 255.255.224.0
R1 R2
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Stub Areas
• Hide external routes, reduce database
• Consolidate external links - 0.0.0.0
Area 1 Area 0Area 2
0.0.0.0
BGPStub Area172.20.64.0 - 172.20.95.0
255.255.255.0
External AS
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Stub Area Restrictions
X
External AS
0.0.0.0
Area 2
• single exit point or, if multiple exit points,
suboptimal path acceptable
• Transit area for virtual links disallowed
• An ASBR cannot be internal to stube
Single Exit Point
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Totally Stubby Areas
• Block external and summary routes
• Know only intra-area and default routes
Area 1 Area 0Area 2
0.0.0.0
BGPStub Area172.20.64.0 - 172.20.95.0
255.255.255.0
External AS
Summary (IA) Route
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OSPF Stub Area Commands
Router (config-router ) #
Area area-id stub [no-summary]Area area-id stub [no-summary]
Creates a stub network
Router (config-router ) #
Area area-id default-cost costArea area-id default-cost cost
• Specifies cost for default route sent into stub area
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OSPF Stub Area Example
External AS
Area 0
Stub Area 2
192.168.15.2192.168.15.1
192.168.14.1
E0 S0
S0
R3
R4
R3#interface Ethernet 0ip address 192.168.14.1 255.255.255.0interface Serial 0ip 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
R3#interface Ethernet 0ip address 192.168.14.1 255.255.255.0interface Serial 0ip 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 0ip address 192.168.15.2 255.255.255.252
router ospf 15network 192.168.15.0 0.0.0.255 area 2area 2 stub
R4#interface Serial 0ip address 192.168.15.2 255.255.255.252
router ospf 15network 192.168.15.0 0.0.0.255 area 2area 2 stub
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OSPF Totally Stubby Example
External AS
Area 0
Stub Area 2
192.168.15.2192.168.15.1
192.168.14.1
E0 S0
S0
R3
R4
R3#
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 no-summaryarea 2 stub default-cost 20
R3#
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 no-summaryarea 2 stub default-cost 20
R4#
router ospf 15network 192.168.15.0 0.0.0.255 area 2area 2 stub
R4#
router ospf 15network 192.168.15.0 0.0.0.255 area 2area 2 stub
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OSPF Route Redistribution
RIP
IGRP
Enhanced IGRP
IS-IS
OSPF
BGP EGP
• Allows routing-information exchange between OSPF and other routing protocols
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OSPF redistribution Command
Router (config-router ) #
Redistribute protocol [ process-id ] [ metric value ] [ metric-type value ] [ subnet ]
Redistribute protocol [ process-id ] [ metric value ] [ metric-type value ] [ subnet ]
Redistributes routes from OSPF into other routing protocols
(and vice versa)
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OSPF Redistribution Example 1
RIP OSPF Area 0
172.16.62.1172.16.9.1 S0
S1R1
172.16.8.1 172.16.63.1
Redistribution between RIP and OSPF
router ospf 109network 172.16.62.0 0.0.0.255 area 0network 172.16.63.0 0.0.0.255 area 0redistribute rip subnets metric-type 1 metric 20
router ripnetwork 172.16.0.0passive-interface serial 0passive-interface serial 1default-metric 10redistribute ospf match internal external 1 external 2
router ospf 109network 172.16.62.0 0.0.0.255 area 0network 172.16.63.0 0.0.0.255 area 0redistribute rip subnets metric-type 1 metric 20
router ripnetwork 172.16.0.0passive-interface serial 0passive-interface serial 1default-metric 10redistribute ospf match internal external 1 external 2
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Redistribution Example 2
“Back door” creates potential loop
RIP RIP
RIP
OSPF Area 0
R1
R2
R3
172.16.9.1
172.16.8.1
router ospf 109network 172.16.62.0 0.0.0.255 area 0network 172.16.63.0 0.0.0.255 area 0redistribute rip subnets metric-type 1 metric 20distribute-list 11 out rip
access-list 11 permit 172.16.8.0 0.0.7.255
router ospf 109network 172.16.62.0 0.0.0.255 area 0network 172.16.63.0 0.0.0.255 area 0redistribute rip subnets metric-type 1 metric 20distribute-list 11 out rip
access-list 11 permit 172.16.8.0 0.0.7.255
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Verifying OSPF Operation
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Show ip ospf interface Command
• Verifies interfaces are in correct areas
Router# show ip ospf interface e 0 Ethernet 0 is up, line protocol is up Internet Address 203.250.14.1 255.255.255.0, Area 0.0.0.0 Process ID 10, Router ID 203.250.13.41, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State BDR, Priority l Designated Router (ID) 203.250.15.1, Interfece address 203.250.14.2 Backup Designated router (ID) 203.250.13.41, interface address 203.250.14.1 Timer intervale configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 0:00:02 Neighbor Count is 3, Adjacent neighbor count is 3 Adjacent with neighbor 203.250.15.1 (Designated Router) Loopback0 is up, line protocol is up Internet address 203.250.13.41 255.255.255.255, Area 1 Process ID 10, Router ID 203.250.13.41, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host
Router# show ip ospf interface e 0 Ethernet 0 is up, line protocol is up Internet Address 203.250.14.1 255.255.255.0, Area 0.0.0.0 Process ID 10, Router ID 203.250.13.41, Network Type BROADCAST, Cost: 10 Transmit Delay is 1 sec, State BDR, Priority l Designated Router (ID) 203.250.15.1, Interfece address 203.250.14.2 Backup Designated router (ID) 203.250.13.41, interface address 203.250.14.1 Timer intervale configured, Hello 10, Dead 40, Wait 40, Retransmit 5 Hello due in 0:00:02 Neighbor Count is 3, Adjacent neighbor count is 3 Adjacent with neighbor 203.250.15.1 (Designated Router) Loopback0 is up, line protocol is up Internet address 203.250.13.41 255.255.255.255, Area 1 Process ID 10, Router ID 203.250.13.41, Network Type LOOPBACK, Cost: 1 Loopback interface is treated as a stub Host
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Show ip ospf Command
Router # show ip ospf Routing Process "ospf 1" with ID 2.2.2.2 Supports only single TOS (TOS0) routes SPF schedule delay 5 secs, Hold time between two SPFs 10 secs Number of areas in this router is 1 Area 23
Number of interfaces in this area is 3 Area has no authenticationSPF algorithm executed 19 times Area ranges areLink State Update Interval is 0:30:00 and due in 0:04:55 Link State Age Interval is 0:20:00 and due in 0:04:55
Router # show ip ospf Routing Process "ospf 1" with ID 2.2.2.2 Supports only single TOS (TOS0) routes SPF schedule delay 5 secs, Hold time between two SPFs 10 secs Number of areas in this router is 1 Area 23
Number of interfaces in this area is 3 Area has no authenticationSPF algorithm executed 19 times Area ranges areLink State Update Interval is 0:30:00 and due in 0:04:55 Link State Age Interval is 0:20:00 and due in 0:04:55
• Displays general information about the OSPF routing process
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show ip ospf database Command
Router# show ip ospf database OSPF Router with ID (3.3.3.3) (Process ID 1)
Router Link States (Area 23)Link ID ADV Age Seq# Checksum Link
Router count3.3.3.3 3.3.3.3 78 0x80000032 0x8086 54.4.4.4 4.4.4.4 1691 0x80000028 0xEllC 12.2.2.2 2.2.2.2 1693 0x80000030 0x835E 51.1.1.1 1.1.1.1 1696 0x80000026 0x80A1 1
Net Link States (Area 23)
Link ID ADV Router Age Seg# Checksum150.100.4.2 4.4.4.4 1691 0x80000030 0x2FCE150.100.1.2 2.2.2.2 1693 0x80000024 0xFB29
Router# show ip ospf database OSPF Router with ID (3.3.3.3) (Process ID 1)
Router Link States (Area 23)Link ID ADV Age Seq# Checksum Link
Router count3.3.3.3 3.3.3.3 78 0x80000032 0x8086 54.4.4.4 4.4.4.4 1691 0x80000028 0xEllC 12.2.2.2 2.2.2.2 1693 0x80000030 0x835E 51.1.1.1 1.1.1.1 1696 0x80000026 0x80A1 1
Net Link States (Area 23)
Link ID ADV Router Age Seg# Checksum150.100.4.2 4.4.4.4 1691 0x80000030 0x2FCE150.100.1.2 2.2.2.2 1693 0x80000024 0xFB29
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show ip protocol CommandRouter> show ip protocol Routing Protocol is "ospf 300" Sendinq updates every 0 seconds Invalid after 0 seconds, hold down 0, flushed after 0 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Redistributing: ospf 300Routing for Networks: 183.8.0.0/0.0.255.255 144.253.100.0/0.0.0.255Routing Information Sources: Gateway Distance Last Update 14d.253.100.0 110 6d21 183.8.128.12 110 0:17:32 192.3.63.192 110 0:17:33 153.50.193.1 110 0:17:33 183.8.6d.130 110 6d19 183.8.64.128 110 0:17:33 133.3.4.0 110 0:17:33 131.108.100.3 110 0:17:33 Distance: (default is 1l0) - - More - -
Router> show ip protocol Routing Protocol is "ospf 300" Sendinq updates every 0 seconds Invalid after 0 seconds, hold down 0, flushed after 0 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Redistributing: ospf 300Routing for Networks: 183.8.0.0/0.0.255.255 144.253.100.0/0.0.0.255Routing Information Sources: Gateway Distance Last Update 14d.253.100.0 110 6d21 183.8.128.12 110 0:17:32 192.3.63.192 110 0:17:33 153.50.193.1 110 0:17:33 183.8.6d.130 110 6d19 183.8.64.128 110 0:17:33 133.3.4.0 110 0:17:33 131.108.100.3 110 0:17:33 Distance: (default is 1l0) - - More - -
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Other OSPF show CommandsRouter#
show ip ospf virtual-linksshow ip ospf virtual-links
• Displays parameters about OSPF virtual links
Router#
show ip ospf neighbor detailshow ip ospf neighbor detail
• Displays neighbor information per interface
Router#
show ip ospf border-routersshow ip ospf border-routers
• Displays routes to the ABR and ASBR
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Summary
OSPF is a scalable, standards-based link-state routing protocol
OSPF features:
Hierarchical design
VLSM support
Vendor interoperability
Route summarization
Route redistribution