Open Shortest Path First

1
Open Shortest Path First OSPF (Part 2) George
Macri E-mail gmacri_at_homemail.com 6th CEENET
Workshop, Budapest 2000
2
Interior IP Routing Protocols
3
IP Routing Configuration Tasks
Network 172.30.0.0
4
IP Routing Configuration Tasks

• Global configuration
• Select routing protocol(s)
• Specify network(s)
• Interface configuration
• Verify address/subnet mask

Network 172.16.0.0
RIP
Network 160.89.0.0
RIP
Network 172.30.0.0
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Dynamic Routing Configuration
Router (config)
router protocol keyword

• Defines an IP routing protocol

6
CONFIGURING OSPF
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OSPF Basic Configuration Commands

• Enables an OSPF routing process

8
OSPF Basic Configuration Example
9
OSPF Route Summarization

• Minimizes routing table entries
• Localizes impact of a topology change

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Route Summarization (cont.)

• Inter-area (IA) summary link carries mask
• One entry can represent several subnets

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Route Summarization Issue
Existing Subnet
1111 11 000000 11 00
Mask 252Address 12
Valid 3rd Subnet
131.108.12.0
255.255.252.0
Summary Route
Mask 240Address 12
1111 00000000 1100
Invalid Subnet Zero
255.255.240.0
131.108.12.0

• Some addresses may need reallocating

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Route Summarization Commands

• Consolidates IA routes on an ABR

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Route Summarization Example
14
OSPF Route Redistribution
RIP IGRP Enhanced IGRP IS-IS

• Allows routing-information exchange between OSPF
  and other routing protocols

15
OSPF Redistribution Command

• Redistributes routes from OSPF into other routing
  protocols (and vice versa)

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OSPF Redistribution Example 1
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OSPF Redistribution Example 1
router ospf 109 network 172.16.62.0 0.0.0.255
area 0 network 172.16.63.0 0.0.0.255 area
0 redistribute rip subnets metric-type 1 metric
20 router rip network 172.16.0.0 passive-interfa
ce serial 0 passive-interface serial
1 default-metric 10 redistribute ospf 109 match
internal external 1 external 2
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Redistribution Example 2
"Back door" creates potential loop
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Redistribution Example 2 cont
router ospf 109 network 172.16.62.0 0.0.0.255
area 0 network 172.16.63.0 0.0.0.255 area
0 redistribute rip subnets metric-type 1 metric
20 distribute-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
Router show ip ospf interface e 0 Ethernet0 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 1 Designated Router
(ID) 203.250.15.1, Interface address
203.250.14.2 Backup Designated router (ID)
203.250.13.41, Interface address 203.250.14.1
Timer intervals configured, Hello 10, Dead 40,
Wait 40, Retransmit 5 Hello due in 00002
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

• Verifies interfaces are in correct areas

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show ip ospf Command

• Displays general information about the OSPF
  routing process

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show ip ospf database Command
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show ip protocol Command
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Other OSPF show Commands

• Displays parameters about OSPF virtual links