Open Shortest Path FirstOSPF

(Part 2)

George MacriE-mail: gmacri@homemail.com

6th CEENET Workshop, Budapest 2000

Interior IP Routing Protocols

Routing Information Protocol (RIP)

Interior Gateway RoutingProtocol (IGRP)

Open Shortest Path First (OSPF) Protocol

Enhanced IGRP (EIGRP)

Routing Information Protocol (RIP)

Interior Gateway RoutingProtocol (IGRP)

Open Shortest Path First (OSPF) Protocol

Enhanced IGRP (EIGRP)

Application

Transport

Internet

Network Interface

Hardware

IP Routing Configuration Tasks

Network 172.30.0.0

IGRP,RIP

• Global configuration

Select routing protocol(s)

Network 160.89.0.0

Network 172.16.0.0

Specify network(s)

IP Routing Configuration Tasks

Network 172.30.0.0

Network 160.89.0.0

IGRP,RIP

Network 172.16.0.0

RIP

RIP

• Global configuration

Select routing protocol(s)

Specify network(s)

• Interface configuration

Verify address/subnet mask

• Defines an IP routing protocol

router protocol [ keyword ]

Router (config) #

Dynamic Routing Configuration

network network-numberRouter (config-router) #

• The network subcommand is a mandatory configuration command for each IP routing process

CONFIGURING OSPFCONFIGURING OSPF

Router (config) #

router ospf process-id

OSPF Basic Configuration Commands

• Enables an OSPF routing process

Router (config-router) #

network address wildcard-mask area area-id

• Selects participating interfaces

OSPF Basic Configuration Example

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

Area 0

Area 1

172.16.1.1

172.16.3.2

192.168.10.5 E1

T0

E0

172.16.5.3E2

TokenRing

• Minimizes routing table entries

• Localizes impact of a topology change

OSPF Route Summarization

Area 0 Backbone

ABRs

Area 1

Summarization

xx

O 131.108.4.0 255.255.252.0O 131.108.8.0 255.255.252.0O 131.108.12.0 255.255.252.0O 131.108.16.0 255.255.252.0O 131.108.20.0 255.255.252.0O 131.108.24.0 255.255.252.0O 131.108.28.0 255.255.252.0

Routing Table for B

Routing Table for C

IA 131.108.16.0 255.255.240.0

• Inter-area (IA) summary link carries mask

• One entry can represent several subnets

Route Summarization (cont.)

Area 1 Area 0ABR

Summarization

BA C

Summary Route

131.108.12.0 255.255.240.0Mask = 240Address = 12

Existing Subnet

131.108.12.0 255.255.252.0

Mask = 252Address = 12

1111 11 000000 11 00

1111 00000000 1100

Valid 3rd Subnet

Invalid Subnet Zero

• Some addresses may need reallocating

Route Summarization Issue

Router (config-router) #

area area-id range address mask

Route Summarization Commands

• Consolidates IA routes on an ABR

Router (config-router) #

summary-address address mask

• Consolidates external routes on an ASBR

Route Summarization Example

R2

R2#

router ospf 100

network 172.16.64.0 0.0.31.255 area 2

network 172.16.96.0 0.0.31.255 area 0

area 0 range 172.16.96.0 255.255.224.0

area 2 range 172.16.64.0 255.255.224.0

R1#

router ospf 100

network 172.16.32.0 0.0.31.255 area 1

network 172.16.96.0 0.0.31.255 area 0

area 0 range 172.16.96.0 255.255.224.0

area 1 range 172.16.32.0 255.255.224.0

172.16.64.0 - 172.16.95.0

255.255.255.0

Area 2

172.16.64.1

172.16.96.0 - 172.16.127.0

255.255.255.0 172.16.127.1172.16.96.1

172.16.32.0 - 172.16.63.0

255.255.255.0

Area 1

172.16.32.1

Interface Addresses(255.255.255.0 mask)

Interface Addresses(255.255.255.0 mask)

R1 R2

Area 0

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

OSPF Route Redistribution

OSPF

RIPIGRPEnhanced IGRPIS-IS

BGPEGP

Router (config-router) #

redistribute protocol [ process-id ] [ metric value ] [ metric-type value ] [ subnets ]

OSPF Redistribution Command

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

OSPF Redistribution Example 1

Redistribution between RIP and OSPF

RIP

172.16.9.1

172.16.8.1

172.16.62.1

172.16.63.1

OSPF Area 0

S0

S1R1

OSPF Redistribution Example 1OSPF Redistribution Example 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 20

router ripnetwork 172.16.0.0passive-interface serial 0passive-interface serial 1default-metric 10redistribute ospf 109 match internal external 1 external 2

Redistribution Example 2

"Back door" creates potential loopRIP

RIP

172.16.9.1

172.16.8.1

OSPF Area 0

RIP

Avoiding Loops

R2

R3

R2

R1

Redistribution Example 2 contRedistribution Example 2 cont

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 distribute-list 11 out rip

access-list 11 permit 172.16.8.0 0.0.7.255

VERIFYING OSPF OPERATIONVERIFYING OSPF OPERATION

• Verifies interfaces are in correct areas

Router# show ip ospf interface e 0Ethernet0 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 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

show ip ospf interface Command

• Displays general information about the OSPF routing process

Router # show ip ospfRouting Process "ospf 1" with ID 2.2.2.2Supports only single TOS (TOS0) routesSPF schedule delay 5 secs, Hold time between two SPFs 10 secsNumber of areas in this router is 1

Area 23Number of interfaces in this area is 3Area has no authenticationSPF algorithm executed 19 timesArea ranges areLink State Update Interval is 0:30:00 and due in 0:04:55Link State Age Interval is 0:20:00 and due in 0:04:55

show ip ospf 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 Router

Age Seq#

3.3.3.3 3.3.3.3 78 0x800000324.4.4.4 4.4.4.4 1691 0x8000002B 12.2.2.2 2.2.2.2 1693 0x80000030

Checksum

0x80B60xE11C0xE35E

Link count

5

51.1.1.1 1.1.1.1 1696 0x80000026 0x80A1 1

Net Link States (Area 23)

Link ID ADV Router Age Seq# Checksum150.100.4.2 4.4.4.4 1691 0x80000030 0x2FCE150.100.1.2 2.2.2.2 1693 0x80000024 0xFB29

show ip ospf database Command

Router> show ip protocolRouting Protocol is “ospf 300”

Sending updates every 0 secondsInvalid after 0 seconds, hold down 0, flushed after 0Outgoing update filter list for all interfaces is not setIncoming update filter list for all interfaces is not setRedistributing: ospf 300

Routing for Networks:183.8.0.0/0.0.255.255144.253.100.0/0.0.0.255

Routing Information Sources:Gateway Distance Last Update144.253.100.0 110 6d21183.8.128.12 110 0:17:32192.3.63.192 110 0:17:33192.3.63.194 110 0:17:33183.8.128.0 110 6d21153.50.192.0 110 0:17:33153.50.193.1 110 0:17:33183.8.64.130 110 6d19183.8.64.128 110 0:17:33133.3.4.0 110 0:17:33131.108.100.3 110 0:17:33

Distance: (default is 110)- - More - -

show ip protocol Command

Router #

show ip ospf virtual-links

Other OSPF show Commands

• Displays parameters about OSPF virtual links

Router #

show ip ospf neighbor detail

• Displays neighbor information per interfaceRouter #

show ip ospf border-routers

• Displays routes to the ABR and ASBR