OSPF

네트워크

OSPF

Dr.Ratel 2020. 7. 15. 17:23

　　OSPF(Open Shortest Path First)

- Cisco 전용 라우팅 프로토콜

- Advanced Distance Vector

　　라우팅 업데이트 및 관리 방식 / 라우팅 업데이트시 목적지 네트워크, 넥스트-홉, 메트릭 정보 포함

- Classless Routing Protocol

　　서브넷 처리 방식 / 네트워크을 서브넷 마스크를 확인후 서브넷 처리 / 라우팅 업데이트 정보에 서브넷 마스크 포함

- VLSM, CIDR

　　VLSM:서브넷팅된 서브넷을 또 다시 서브넷팅하는 계산 작업

- IGP

　　사용하는 지역 / 컨버전스가 빨라 라우팅 업데이트가 빠르다 / 대용량 라우팅 업데이트 X / 특정 네트워크 구간, AS 안에서 사용

- SPF 알고리즘을 사용하는 개방된 라우팅 프로토콜

1. 라우터 아이디(Router-ID)

- OSPF 라우터를 구분하기 위한 식별자

- 형식 : IPv4 주소 형식

1) 물리적인 인터페이스만 있을 경우, 그 중에 IP 주소가 가장 높은 IP 주소로 선출

F0/0 : 13.13.10.1

S1/0 : 13.13.12.1 <- 라우터 아이디 선출

2) Loopback 인터페이스가 있을 경우, Loopback 중에 IP 주소가 가장 높은 IP 주소로 선출

F0/0 : 13.13.10.1

S1/0 : 13.13.12.1

Lo172 : 172.16.1.1 <- 라우터 아이디 선출

- 단, Down 상태인 인터페이스 IP 주소로는 선출하지 않는다.

3) 'router-id' 명령어를 이용한 수동 선출

R1(config)# router ospf 1

R1(config-router)# router-id 1.1.1.1 ←형식이 IPv4랑 같을 뿐 의미 없음

2. OSPF 설정

Router(config)# router ospf [1~65535 Process-ID]

Router(config-router)# router-id x.x.x.x

Router(config-router)# network [로컬 네트워크] [와일드카드 마스크] area [area 주소] ←OSPF망 설계시 정해짐

Router(config-router)# passive-interface [Interface Name]

와일드카드 마스크 : 서브넷마스크랑 반대로

e.g

서브넷 마스크　　　　　　와일드카드 마스크: 공통비트는 0 다른비트는 1

255.255.255.255　　　　　　0.0.0.0

255.255.255.0　　　　　　　0.0.0.255

255.255.0.0　　　　　　　　0.0.255.255

255.0.0.0　　　　　　　　　0.25.255.255

0.0.0.0　　　　　　　　　　255.255.255.255

@ R1

router ospf 1

router-id 1.1.1.1

network 13.13.10.0 0.0.0.255 area 0

network 13.13.12.0 0.0.0.255 area 0

network 172.16.1.0 0.0.0.255 area 0

passive-interface fa0/0

passive-interface lo172

@ R2

router ospf 1

router-id 2.2.2.2

network 13.13.20.0 0.0.0.255 area 0

network 13.13.12.0 0.0.0.255 area 0

network 13.13.23.0 0.0.0.255 area 0

passive-interface fa0/0

@ R3

router ospf 1

router-id 3.3.3.3

network 13.13.30.0 0.0.0.255 area 0

network 13.13.23.0 0.0.0.255 area 0

network 172.16.3.0 0.0.0.255 area 0

passive-interface fa0/0

passive-interface lo172

R1,R2,R3#show run

R1,R2,R3#show ip ospf neighbor

R1,R2,R3#show ip route

R1#ping 13.13.20.1 source fa0/0

R1#ping 13.13.30.1 source fa0/0

R1#ping 172.16.3.1 source lo172

R2#ping 13.13.10.1 source fa0/0

R2#ping 172.16.1.1 source fa0/0

R2#ping 13.13.30.1 source fa0/0

R2#ping 172.16.3.1 source fa0/0

R3#ping 13.13.20.1 source fa0/0

R3#ping 13.13.10.1 source fa0/0

R3#ping 172.16.1.1 source lo172

3. Loopback /32 라우팅 업데이트 동작

R2#sh ip route ospf

172.16.0.0/32 is subnetted, 2 subnets

O 172.16.1.1 [110/65] via 13.13.12.1, 00:00:50, Serial1/1

O 172.16.3.1 [110/65] via 13.13.23.3, 00:00:50, Serial1/0

13.0.0.0/24 is subnetted, 5 subnets

O 13.13.10.0 [110/74] via 13.13.12.1, 00:00:50, Serial1/1

O 13.13.30.0 [110/74] via 13.13.23.3, 00:00:50, Serial1/0

R1#show ip ospf int lo 172

Loopback172 is up, line protocol is up

Internet Address 172.16.1.1/24, Area 0

Process ID 1, Router ID 1.1.1.1, Network Type LOOPBACK, Cost: 1

Loopback interface is treated as a stub Host

--------------- IP 1개 네트워크(255.255.255.255 = /32)

R1(config)#int lo 172

R1(config-if)#ip ospf network point-to-point

R1(config-if)#end

R1#show ip ospf int lo 172

Loopback172 is up, line protocol is up

Internet Address 172.16.1.1/24, Area 0

Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1

Transmit Delay is 1 sec, State POINT_TO_POINT

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

oob-resync timeout 40

~ 중간 생략 ~

R2#sh ip route ospf

172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks

O 172.16.1.0/24 [110/65] via 13.13.12.1, 00:00:55, Serial1/1

O 172.16.3.1/32 [110/65] via 13.13.23.3, 00:00:55, Serial1/0

13.0.0.0/24 is subnetted, 5 subnets

O 13.13.10.0 [110/74] via 13.13.12.1, 00:00:55, Serial1/1

O 13.13.30.0 [110/74] via 13.13.23.3, 00:00:55, Serial1/0

R3(config)#int lo 172

R3(config-if)#ip ospf network point-to-point

R3(config-if)#end

R2#sh ip route ospf

172.16.0.0/24 is subnetted, 2 subnets

O 172.16.1.0 [110/65] via 13.13.12.1, 00:00:01, Serial1/1

O 172.16.3.0 [110/65] via 13.13.23.3, 00:00:01, Serial1/0

13.0.0.0/24 is subnetted, 5 subnets

O 13.13.10.0 [110/74] via 13.13.12.1, 00:00:01, Serial1/1

O 13.13.30.0 [110/74] via 13.13.23.3, 00:00:01, Serial1/0

4. OSPF 메트릭

- Cost = 10^8 / Bandwidth

Ex) R1에서 '13.13.30.0/24'까지 OSPF 메트릭(Cost)은 얼마인가?

1544k 1544k 10M

R1---------------------------R2--------------------------R3-----------------| 13.13.30.0/24

cost = 64 cost = 64 cost = 10

64 + 64 + 10 = 138

R1#show ip ospf int s1/0

R2#show ip ospf int s1/0

R3#show ip ospf int fa0/0

R1#show ip route 13.13.30.0

Routing entry for 13.13.30.0/24

Known via "ospf 1", distance 110, metric 138, type intra area

Last update from 13.13.12.2 on Serial1/0, 00:06:14 ago

Routing Descriptor Blocks:

* 13.13.12.2, from 3.3.3.3, 00:06:14 ago, via Serial1/0

Route metric is 138, traffic share count is 1

5. OSPF 신뢰도

R1#show ip route ospf

172.16.0.0/24 is subnetted, 2 subnets

O 172.16.3.0 [110/129] via 13.13.12.2, 00:06:43, Serial1/0

13.0.0.0/24 is subnetted, 5 subnets

O 13.13.20.0 [110/74] via 13.13.12.2, 00:06:43, Serial1/0

O 13.13.23.0 [110/128] via 13.13.12.2, 00:06:43, Serial1/0

O 13.13.30.0 [110/138] via 13.13.12.2, 00:06:43, Serial1/0

[참고] 경로 신뢰도

Connected 0

Static 1

EIGRP 90

OSPF 110

RIP 120

EIGRP External 170

6. OSPF 동작 과정

- '@ OSPF 동작 과정.ppt' 참조

- Down state -> Init state -> Two-Way state -> Exstart state -> Exchange state -> Loading state - Full state

Down state:Hello 보냄 ACK

Init state: ACK/SNK

Two-Way state:ACK

→→→→→→→→→→→→→→→→→→→→→→→→→TCP처럼 본론 전 준비 단계

Exstart state Router ID 높은애가 Master 낮은애가 Slave

Exchange state: LinkStateDataBase

Loading state: Slave Router가 없는 정보를 LSR을 통해 Mater Router에게 정보를 요청함

Full state:정보를 받으면 ACK를 보냄

R1#debug ip ospf adj

OSPF adjacency events debugging is on

R1#

R1#clear ip ospf process

Reset ALL OSPF processes? [no]: yes

R1#

*Mar 1 00:49:57.903: OSPF: Interface Loopback172 going Down

*Mar 1 00:49:57.903: OSPF: 1.1.1.1 address 172.16.1.1 on Loopback172 is dead, state DOWN

*Mar 1 00:49:57.907: OSPF: Interface FastEthernet0/0 going Down

*Mar 1 00:49:57.911: OSPF: 1.1.1.1 address 13.13.10.1 on FastEthernet0/0 is dead, state DOWN

*Mar 1 00:49:57.911: OSPF: Neighbor change Event on interface FastEthernet0/0

*Mar 1 00:49:57.915: OSPF: DR/BDR election on FastEthernet0/0

*Mar 1 00:49:57.915: OSPF: Elect BDR 0.0.0.0

*Mar 1 00:49:57.915: OSPF: Elect DR 0.0.0.0

*Mar 1 00:49:57.919: OSPF: Elect BDR 0.0.0.0

*Mar 1 00:49:57.919: OSPF: Elect DR 0.0.0.0

*Mar 1 00:49:57.923: DR: none BDR: none

*Mar 1 00:49:57.923: OSPF: Flush network LSA immediately

*Mar 1 00:49:57.927: OSPF: Remember old DR 1.1.1.1 (id)

*Mar 1 00:49:57.927: OSPF: Interface Serial1/0 going Down

*Mar 1 00:49:57.931: OSPF: 1.1.1.1 address 13.13.12.1 on Serial1/0 is dead, state DOWN

*Mar 1 00:49:57.931: OSPF: 2.2.2

R1#.2 address 13.13.12.2 on Serial1/0 is dead, state DOWN

*Mar 1 00:49:57.935: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial1/0 from FULL to DOWN, Neighbor Down: Interface down or detached

*Mar 1 00:49:58.571: OSPF: Interface Loopback172 going Up

*Mar 1 00:49:58.575: OSPF: Interface FastEthernet0/0 going Up

*Mar 1 00:49:58.575: OSPF: Interface Serial1/0 going Up

*Mar 1 00:49:58.591: OSPF: Build router LSA for area 0, router ID 1.1.1.1, seq 0x80000001, process 1

*Mar 1 00:49:58.595: OSPF: We are not DR to build Net Lsa for interface FastEthernet0/0

*Mar 1 00:49:58.603: OSPF: 2 Way Communication to 2.2.2.2 on Serial1/0, state 2WAY

*Mar 1 00:49:58.603: OSPF: Send DBD to 2.2.2.2 on Serial1/0 seq 0x2A2 opt 0x52 flag 0x7 len 32

*Mar 1 00:49:58.627: OSPF: Rcv DBD from 2.2.2.2 on Serial1/0 seq 0x26DD opt 0x52 flag 0x7 len 32 mtu 1500 state EXSTART

*Mar 1 00:49:58.631: OSPF: NBR Negotiation Done. We are the SLAVE

*Mar 1 00:49:58.635: OSPF: Send DBD to 2.2.2.2 on Serial1/

R1#0 seq 0x26DD opt 0x52 flag 0x2 len 52

*Mar 1 00:49:58.675: OSPF: Rcv DBD from 2.2.2.2 on Serial1/0 seq 0x26DE opt 0x52 flag 0x3 len 72 mtu 1500 state EXCHANGE

*Mar 1 00:49:58.679: OSPF: Send DBD to 2.2.2.2 on Serial1/0 seq 0x26DE opt 0x52 flag 0x0 len 32

*Mar 1 00:49:58.739: OSPF: Rcv DBD from 2.2.2.2 on Serial1/0 seq 0x26DF opt 0x52 flag 0x1 len 32 mtu 1500 state EXCHANGE

*Mar 1 00:49:58.743: OSPF: Exchange Done with 2.2.2.2 on Serial1/0

*Mar 1 00:49:58.747: OSPF: Send LS REQ to 2.2.2.2 length 24 LSA count 2

*Mar 1 00:49:58.747: OSPF: Send DBD to 2.2.2.2 on Serial1/0 seq 0x26DF opt 0x52 flag 0x0 len 32

*Mar 1 00:49:58.815: OSPF: Rcv LS UPD from 2.2.2.2 on Serial1/0 length 184 LSA count 2

*Mar 1 00:49:58.819: OSPF: Synchronized with 2.2.2.2 on Serial1/0, state FULL

*Mar 1 00:49:58.823: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial1/0 from LOADING to FULL, Loading Done

R1#

*Mar 1 00:50:03.971: OSPF: Rcv LS UPD from 2.2.2.2 on Serial1/0 length 100 LSA count 1

*Mar 1 00:50:04.327: OSPF: Build router LSA for area 0, router ID 1.1.1.1, seq 0x80000005, process 1

R1#

R1#undebug all

All possible debugging has been turned off

R1#

7. OSPF 라우팅 업데이트 및 변경 사항

- 네트워크 추가 및 삭제될 경우, LSU 패켓을 통해서 업데이트 실시

8. Area 설계

- OSPF 광고양을 최소화하기 위해서 Area 설계를 실시한다.

- 같은 Area 안에서는 전체 광고되지만, 다른 Area로는 추가/삭제된 부분만 광고한다.

- Area 설계 방법 : 모든 Area는 Area 0을 경유하도록 설계해야 한다.

- Area 0 = Backbone Area (모든 Area가 경유하는 Area)

- ABR = Area 0과 Area X 사이에 있는 라우터

- ASBR = 외부 네트워크 정보를 OSPF 환경으로 라우팅 업데이트하는 라우터

9. OSPF 테이블 유형

1) 네이버 테이블

R1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

2.2.2.2 0 FULL/ - 00:00:30 13.13.12.2 Serial1/0

2) 데이터베이스 테이블(Link-State Database = LSDB)

R1#show ip ospf database

OSPF Router with ID (1.1.1.1) (Process ID 1)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count

1.1.1.1 1.1.1.1 50 0x80000006 0x00E351 4

2.2.2.2 2.2.2.2 51 0x80000007 0x008064 5

3.3.3.3 3.3.3.3 840 0x80000004 0x007682 4

@ R3 Area 0 링크 - 4개

13.13.23.0/24

13.13.30.0/24

172.16.3.0/24

R2와 연결된 S1/1 주소 13.13.23.3

@ R2 Area 0 링크 - 5개

13.13.12.0/24

13.13.20.0/24

13.13.23.0/24

R3와 연결된 S1/0 주소 13.13.23.2

R1과 연결된 S1/1 주소 13.13.12.2

@ R1 Area 0 링크 - 4개

13.13.10.0/24

13.13.12.0/24

172.16.1.0/24

R2와 연결된 S1/0 주소 13.13.12.1

R1#show ip ospf database router

OSPF Router with ID (1.1.1.1) (Process ID 1)

Router Link States (Area 0)

LS age: 271

Options: (No TOS-capability, DC)

LS Type: Router Links

Link State ID: 1.1.1.1

Advertising Router: 1.1.1.1

LS Seq Number: 80000006

Checksum: 0xE351

Length: 72

Number of Links: 4

Link connected to: a Stub Network

(Link ID) Network/subnet number: 172.16.1.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 1

Link connected to: another Router (point-to-point)

(Link ID) Neighboring Router ID: 2.2.2.2

(Link Data) Router Interface address: 13.13.12.1

Number of TOS metrics: 0

TOS 0 Metrics: 64

Link connected to: a Stub Network

(Link ID) Network/subnet number: 13.13.12.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 64

Link connected to: a Stub Network

(Link ID) Network/subnet number: 13.13.10.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 10

LS age: 273

Options: (No TOS-capability, DC)

LS Type: Router Links

Link State ID: 2.2.2.2

Advertising Router: 2.2.2.2

LS Seq Number: 80000007

Checksum: 0x8064

Length: 84

Number of Links: 5

Link connected to: another Router (point-to-point)

(Link ID) Neighboring Router ID: 1.1.1.1

(Link Data) Router Interface address: 13.13.12.2

Number of TOS metrics: 0

TOS 0 Metrics: 64

Link connected to: a Stub Network

(Link ID) Network/subnet number: 13.13.12.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 64

Link connected to: a Stub Network

(Link ID) Network/subnet number: 13.13.20.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 10

Link connected to: another Router (point-to-point)

(Link ID) Neighboring Router ID: 3.3.3.3

(Link Data) Router Interface address: 13.13.23.2

Number of TOS metrics: 0

TOS 0 Metrics: 64

Link connected to: a Stub Network

(Link ID) Network/subnet number: 13.13.23.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 64

LS age: 1063

Options: (No TOS-capability, DC)

LS Type: Router Links

Link State ID: 3.3.3.3

Advertising Router: 3.3.3.3

LS Seq Number: 80000004

Checksum: 0x7682

Length: 72

Number of Links: 4

Link connected to: a Stub Network

(Link ID) Network/subnet number: 172.16.3.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 1

Link connected to: a Stub Network

(Link ID) Network/subnet number: 13.13.30.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 10

Link connected to: another Router (point-to-point)

(Link ID) Neighboring Router ID: 2.2.2.2

(Link Data) Router Interface address: 13.13.23.3

Number of TOS metrics: 0

TOS 0 Metrics: 64

Link connected to: a Stub Network

(Link ID) Network/subnet number: 13.13.23.0

(Link Data) Network Mask: 255.255.255.0

Number of TOS metrics: 0

TOS 0 Metrics: 64

3) 라우팅 테이블

R1#show ip route ospf

172.16.0.0/24 is subnetted, 2 subnets

O 172.16.3.0 [110/129] via 13.13.12.2, 00:10:32, Serial1/0

13.0.0.0/24 is subnetted, 5 subnets

O 13.13.20.0 [110/74] via 13.13.12.2, 00:10:33, Serial1/0

O 13.13.23.0 [110/128] via 13.13.12.2, 00:10:33, Serial1/0

O 13.13.30.0 [110/138] via 13.13.12.2, 00:10:33, Serial1/0

10. OSPF 경로 유형

- O : Intra-Area 경로, 같은 Area 네트워크

- O IA : Inter-Area 경로, 다른 Area 네트워크

- O E2 : External 경로, 외부 네트워크

R3(config)#int lo 100

R3(config-if)#ip address 100.100.1.1 255.255.255.0

R3(config-if)#ip address 100.100.2.1 255.255.255.0 secondary

R3(config-if)#ip address 100.100.3.1 255.255.255.0 secondary

R3(config-if)#

R3(config-if)#int lo 200

R3(config-if)#ip address 200.200.1.1 255.255.255.0

R3(config-if)#ip address 200.200.2.1 255.255.255.0 secondary

R3(config-if)#ip address 200.200.3.1 255.255.255.0 secondary

R3(config-if)#ip ospf network point-to-point

R3(config-if)#

R3(config-if)#router rip

R3(config-router)#version 2

R3(config-router)#no auto-summary

R3(config-router)#network 100.0.0.0

R3(config-router)#

R3(config-router)#router ospf 1

R3(config-router)#network 200.200.0.0 0.0.255.255 area 13

R3(config-router)#redistribute rip subnets

R1#show ip route ospf

100.0.0.0/24 is subnetted, 3 subnets

O E2 100.100.1.0 [110/20] via 13.13.12.2, 00:04:11, Serial1/0

O E2 100.100.2.0 [110/20] via 13.13.12.2, 00:04:11, Serial1/0

O E2 100.100.3.0 [110/20] via 13.13.12.2, 00:04:11, Serial1/0

O IA 200.200.1.0/24 [110/129] via 13.13.12.2, 00:04:11, Serial1/0

O IA 200.200.2.0/24 [110/129] via 13.13.12.2, 00:04:11, Serial1/0

172.16.0.0/24 is subnetted, 2 subnets

O 172.16.3.0 [110/129] via 13.13.12.2, 00:04:11, Serial1/0

O IA 200.200.3.0/24 [110/129] via 13.13.12.2, 00:04:11, Serial1/0

13.0.0.0/24 is subnetted, 5 subnets

O 13.13.20.0 [110/74] via 13.13.12.2, 00:04:11, Serial1/0

O 13.13.23.0 [110/128] via 13.13.12.2, 00:04:11, Serial1/0

O 13.13.30.0 [110/138] via 13.13.12.2, 00:04:11, Serial1/0

11. ABR, ASBR 라우터 확인

- ABR : Area 0과 Area X 사이에 있는 라우터

- ASBR : 외부 네트워크 정보를 OSPF 환경으로 라우팅 업데이트하는 라우터

R3#show ip ospf

Routing Process "ospf 1" with ID 3.3.3.3

Start time: 00:14:19.748, Time elapsed: 01:11:19.772

Supports only single TOS(TOS0) routes

Supports opaque LSA

Supports Link-local Signaling (LLS)

Supports area transit capability

It is an area border and autonomous system boundary router

Redistributing External Routes from,

rip, includes subnets in redistribution

~ 중간 생략 ~

12. DR/BDR

- '@ OSPF DR&BDR 관련 예제.pkt' 참조

- Multi Access 환경에서 DR/BDR을 선출한다. (단, Point-to-Point 환경은 선출 X) e.g.학교 실습실

- Multi Access 환경 : Ethenet 환경

- DR을 통해서 OSPF 광고를 실시하여, OSPF 광고양을 최소화시킨다.

- DR 선출 과정

① OSPF 우선 순위가 높은 라우터가 DR, 두번째가 BDR / 우선순위가 0이면 절대 DR과 BDR을 안하고 무조건 DROTHER

② 우선순위가 동일할경우OSPF 라우터 아이디가 높은 라우터가 DR, 두번째가 BDR

- DR/BDR 아닌 라우터들은 'DROTHER'라고 한다.

- DR/BDR은 우선 순위를 조정하여 수동 선출하는 것을 권장한다.

- DST IP가 224.0.0.6 일 경우 DR,BDR만 수신

Router(config-if)# ip ospf priority [0~255]

- 우선 순위의 기본값은 '1'이며, 우선 순위가 '0'이면 무조건 DROTHER로 동작한다.

→ AREA 설계는 광고 크기를 줄인다면 DR/BDR은 Multi Access 환경에서 광고 횟수를 줄임 / P2P환경에선 필요없음

R3#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

1.1.1.1 1 2WAY/DROTHER 00:00:37 13.13.100.1 FastEthernet0/1

2.2.2.2 1 2WAY/DROTHER 00:00:37 13.13.100.2 FastEthernet0/1

4.4.4.4 1 FULL/BDR 00:00:37 13.13.100.4 FastEthernet0/1

5.5.5.5 1 FULL/DR 00:00:37 13.13.100.5 FastEthernet0/1

R1>en

R1#conf t

R1(config)#int fa0/1

R1(config-if)#ip ospf priority 255

R2>en

R2#conf t

R2(config)#int fa0/1

R2(config-if)#ip ospf priority 254

@ R3, R4, R5 <- DR/BDR X, 무조건 DROTHER 동작함

int fa0/1

ip ospf priority 0

R3#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

1.1.1.1 255 FULL/DR 00:00:35 13.13.100.1 FastEthernet0/1

2.2.2.2 254 FULL/BDR 00:00:35 13.13.100.2 FastEthernet0/1

4.4.4.4 0 2WAY/DROTHER 00:00:35 13.13.100.4 FastEthernet0/1

5.5.5.5 0 2WAY/DROTHER 00:00:35 13.13.100.5 FastEthernet0/1

13. OSPF 인증

- OSPF 패켓 변조 방지

→대부분 인증 함.

Ex) Area 0 구간에 인증을 실시하여라.

R1(config)#router ospf 1

R1(config-router)#area 0 authentication message-digest

R1(config-router)#

R1(config-router)#int s1/0

R1(config-if)#ip ospf message-digest-key 13 md5 cisco

R2(config)#router ospf 1

R2(config-router)#area 0 authentication message-digest

R2(config-router)#

R2(config-router)#int s1/0

R2(config-if)#ip ospf message-digest-key 13 md5 cisco

R2(config-if)#

R2(config-if)#int s1/1

R2(config-if)#ip ospf message-digest-key 13 md5 cisco

R3(config)#router ospf 1

R3(config-router)#area 0 authentication message-digest

R3(config-router)#

R3(config-router)#int s1/1

R3(config-if)#ip ospf message-digest-key 13 md5 cisco

R1,R2,R3#show run

R1,R2,R3#show ip ospf neighbor

R1,R2,R3#show ip route

- 다음 실습을 위해서 OSPF 및 인증 설정을 삭제하도록 한다.

R1(config)#no router ospf 1

R1(config)#int s1/0

R1(config-if)#no ip ospf message-digest-key 13 md5 cisco

R1(config-if)#exit

R2(config)#no router ospf 1

R2(config)#int s1/0

R2(config-if)#no ip ospf message-digest-key 13 md5 cisco

R2(config-if)#

R2(config-if)#int s1/1

R2(config-if)#no ip ospf message-digest-key 13 md5 cisco

R2(config-if)#exit

R3(config)#no router ospf 1

R3(config)#int s1/1

R3(config-if)#no ip ospf message-digest-key 13 md5 cisco

R3(config-if)#exit

- 그림을 참고하여 OSPF Area 0, Area 13, Area 113을 구성한다.

R1(config)#router ospf 1

R1(config-router)#router-id 1.1.1.1

R1(config-router)#network 13.13.10.0 0.0.0.255 area 0

R1(config-router)#network 13.13.12.0 0.0.0.255 area 0

R1(config-router)#network 172.16.1.0 0.0.0.255 area 0

R1(config-router)#passive-interface fa0/0

R1(config-router)#passive-interface lo172

R1(config-router)#end

R2(config)#router ospf 1

R2(config-router)#router-id 2.2.2.2

R2(config-router)#network 13.13.12.0 0.0.0.255 area 0

R2(config-router)#network 13.13.20.0 0.0.0.255 area 13

R2(config-router)#network 13.13.23.0 0.0.0.255 area 13

R2(config-router)#passive-interface fa0/0

R2(config-router)#end

R3(config)#router ospf 1

R3(config-router)#router-id 3.3.3.3

R3(config-router)#network 13.13.23.0 0.0.0.255 area 13

R3(config-router)#network 13.13.30.0 0.0.0.255 area 13

R3(config-router)#network 172.16.3.0 0.0.0.255 area 113

R3(config-router)#passive-interface fa0/0

R3(config-router)#passive-interface lo172

R3(config-router)#end

R1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

2.2.2.2 0 FULL/ - 00:00:30 13.13.12.2 Serial1/0

R2#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

1.1.1.1 0 FULL/ - 00:00:30 13.13.12.1 Serial1/1

3.3.3.3 0 FULL/ - 00:00:32 13.13.23.3 Serial1/0

R3#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

2.2.2.2 0 FULL/ - 00:00:30 13.13.23.2 Serial1/1

14. Virtual-Link 설정

- Area 0을 경유하지 못하는 Area가 발생할 경우, 사용하는 기능

- R2에서 R3의 Area 113 '172.16.3.0/24' 네트워크 정보가 라우팅 업데이트 됬는지 확인한다.

R2#show ip route ospf

172.16.0.0/24 is subnetted, 1 subnets

O 172.16.1.0 [110/65] via 13.13.12.1, 00:02:01, Serial1/1

13.0.0.0/24 is subnetted, 5 subnets

O 13.13.10.0 [110/74] via 13.13.12.1, 00:02:02, Serial1/1

O 13.13.30.0 [110/74] via 13.13.23.3, 00:00:41, Serial1/0

- 해결 방법 : 버추얼 링크를 이용하여 ABR R2가 갖고 있는 Area 0 정보를 R3에게 동기화 시킴

R2(config)#router ospf 1

R2(config-router)#area 13 virtual-link 3.3.3.3

R2(config-router)#end

R3(config)#router ospf 1

R3(config-router)#area 13 virtual-link 2.2.2.2

R3(config-router)#end

R2#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

3.3.3.3 0 FULL/ - - 13.13.23.3 OSPF_VL0

1.1.1.1 0 FULL/ - 00:00:37 13.13.12.1 Serial1/1

3.3.3.3 0 FULL/ - 00:00:34 13.13.23.3 Serial1/0

R3#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

2.2.2.2 0 FULL/ - - 13.13.23.2 OSPF_VL0

2.2.2.2 0 FULL/ - 00:00:30 13.13.23.2 Serial1/1

R3#show ip ospf virtual-links

Virtual Link OSPF_VL0 to router 2.2.2.2 is up

Run as demand circuit

DoNotAge LSA allowed.

Transit area 13, via interface Serial1/1, Cost of using 64

Transmit Delay is 1 sec, State POINT_TO_POINT,

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Hello due in 00:00:01

Adjacency State FULL (Hello suppressed)

Index 1/2, retransmission queue length 0, number of retransmission 0

First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)

Last retransmission scan length is 0, maximum is 0

Last retransmission scan time is 0 msec, maximum is 0 msec

R3#show ip ospf

Routing Process "ospf 1" with ID 3.3.3.3

Start time: 00:49:27.332, Time elapsed: 00:04:22.676

Supports only single TOS(TOS0) routes

Supports opaque LSA

Supports Link-local Signaling (LLS)

Supports area transit capability

It is an area border router

Router is not originating router-LSAs with maximum metric

Initial SPF schedule delay 5000 msecs

~ 중간 생략 ~

External flood list length 0

IETF NSF helper support enabled

Cisco NSF helper support enabled

Area BACKBONE(0)

Number of interfaces in this area is 1

Area has no authentication

SPF algorithm last executed 00:00:20.880 ago

SPF algorithm executed 3 times

Area ranges are

Number of LSA 10. Checksum Sum 0x055D60

Number of opaque link LSA 0. Checksum Sum 0x000000

Number of DCbitless LSA 0

Number of indication LSA 0

Number of DoNotAge LSA 5

Flood list length 0

Area 13

Number of interfaces in this area is 2

This area has transit capability: Virtual Link Endpoint

Area has no authentication

SPF algorithm last executed 00:00:20.912 ago

SPF algorithm executed 5 times

Area ranges are

Number of LSA 6. Checksum Sum 0x0210BE

Number of opaque link LSA 0. Checksum Sum 0x000000

Number of DCbitless LSA 0

Number of indication LSA 0

Number of DoNotAge LSA 0

Flood list length 0

Area 113

Number of interfaces in this area is 1

Area has no authentication

SPF algorithm last executed 00:00:31.280 ago

SPF algorithm executed 3 times

Area ranges are

Number of LSA 7. Checksum Sum 0x03C8F2

Number of opaque link LSA 0. Checksum Sum 0x000000

Number of DCbitless LSA 0

Number of indication LSA 0

Number of DoNotAge LSA 0

Flood list length 0

R2#show ip route ospf

172.16.0.0/24 is subnetted, 2 subnets

O 172.16.1.0 [110/65] via 13.13.12.1, 00:00:33, Serial1/1

O IA 172.16.3.0 [110/65] via 13.13.23.3, 00:00:33, Serial1/0

13.0.0.0/24 is subnetted, 5 subnets

O 13.13.10.0 [110/74] via 13.13.12.1, 00:00:33, Serial1/1

O 13.13.30.0 [110/74] via 13.13.23.3, 00:00:33, Serial1/0

15. OSPF 네이버 성립 조건

- 같은 네트워크은 동일한 Area에 포함되어야 한다.

- 같은 네트워크은 OSPF Hello/Dead 주기 시간이 동일해야 한다.

- 같은 네트워크은 MTU 사이즈가 동일해야 한다.

- 라우터 아이디가 중복되면 안된다.

R1#show ip ospf int s1/0

Serial1/0 is up, line protocol is up

Internet Address 13.13.12.1/24, Area 0

Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 64

Transmit Delay is 1 sec, State POINT_TO_POINT

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

~ 중간 생략 ~

R1#show int s1/0

Serial1/0 is up, line protocol is up

Hardware is M4T

Internet address is 13.13.12.1/24

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

reliability 255/255, txload 1/255, rxload 1/255

~ 중간 생략 ~

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