OSPF và Dynamic Routing

Dynamic Routing Protocols

Phân loại

IGP (Interior Gateway Protocol):
- Distance Vector: RIP, EIGRP
- Link State: OSPF, IS-IS

EGP (Exterior Gateway Protocol):
- BGP (Border Gateway Protocol)

So sánh:
RIP:    Hop count, max 15 hops, slow convergence
OSPF:   Link state, cost-based, fast convergence
EIGRP:  Hybrid, DUAL algorithm, Cisco proprietary
BGP:    Path vector, Internet routing, policy-based

OSPF Overview

Đặc điểm

- Open standard (RFC 2328 OSPFv2)
- Link-state routing protocol
- Sử dụng Dijkstra SPF algorithm
- Cost = Reference BW / Interface BW
- Reference BW mặc định: 100 Mbps
- Administrative Distance: 110
- Multicast: 224.0.0.5, 224.0.0.6
- Protocol number: 89

OSPF Cost

Cost = 10^8 / Bandwidth (bps)

Interface costs:
Ethernet (10 Mbps):   Cost = 10
FastEthernet (100):   Cost = 1
GigabitEthernet (1G): Cost = 1
10G:                  Cost = 1

Với reference BW 100 Mbps, tất cả >= 100Mbps đều có cost 1

Cấu hình reference BW:
R1(config)# router ospf 1
R1(config-router)# auto-cost reference-bandwidth 10000
# Trên tất cả routers phải giống nhau!

OSPF Areas

Backbone Area: Area 0
Regular Areas: Area 1, 2, 3...
Special:
- Stub: No external routes (LSA 5)
- Totally Stubby: Only default route (Cisco)
- NSSA: Not-So-Stubby Area (Cisco)

Rules:
- Tất cả areas phải kết nối với Area 0
- Nếu không trực tiếp → virtual link
- Area 0 là core của OSPF

OSPF Neighbor States

Down         - Chưa có thông tin
Init         - Nhận được Hello, chưa 2-way
2-Way        - 2-way communication
ExStart      - Bắt đầu trao đổi DBD
Exchange     - Trao đổi DBD packets
Loading      - Trao đổi LSAs
Full         - Đồng bộ database ✓

Hello Packet

Interval:
- Broadcast: 10s
- NBMA: 30s

Dead Interval:
- Broadcast: 40s (4×Hello)
- NBMA: 120s

Phải khớp:
- Hello interval
- Dead interval
- Area ID
- Authentication
- Stub flag
- MTU (khi Exchange)

Cấu hình OSPF cơ bản

Single Area

# R1
R1(config)# router ospf 1
R1(config-router)# router-id 1.1.1.1
R1(config-router)# network 192.168.1.0 0.0.0.255 area 0
R1(config-router)# network 10.0.0.0 0.0.0.3 area 0
R1(config-router)# exit

# R2
R2(config)# router ospf 1
R2(config-router)# router-id 2.2.2.2
R2(config-router)# network 10.0.0.0 0.0.0.3 area 0
R2(config-router)# network 10.0.0.4 0.0.0.3 area 0
R2(config-router)# exit

# R3
R3(config)# router ospf 1
R3(config-router)# router-id 3.3.3.3
R3(config-router)# network 10.0.0.4 0.0.0.3 area 0
R3(config-router)# network 192.168.3.0 0.0.0.255 area 0

Interface-level config (khuyến nghị)

R1(config)# interface gi0/1
R1(config-if)# ip ospf 1 area 0
R1(config-if)# ip ospf priority 100
R1(config-if)# ip ospf cost 10
R1(config-if)# ip ospf hello-interval 10
R1(config-if)# ip ospf dead-interval 40
R1(config-if)# ip ospf authentication message-digest
R1(config-if)# ip ospf message-digest-key 1 md5 Cisco123
R1(config-if)# exit

Verify OSPF

R1# show ip ospf neighbor
R1# show ip ospf neighbor detail
R1# show ip ospf database
R1# show ip ospf interface
R1# show ip ospf interface brief
R1# show ip protocols
R1# show ip route ospf
R1# show ip ospf

Debug OSPF

R1# debug ip ospf adj
R1# debug ip ospf events
R1# debug ip ospf hello
R1# debug ip ospf packet
R1# undebug all

DR/BDR Election

Trên broadcast networks

DR  - Designated Router
BDR - Backup Designated Router
DROther - Các router khác

Election:
1. Priority cao nhất (0-255, default 1)
2. Nếu bằng → Router ID cao nhất
3. Priority = 0 → không tham gia

DRother chỉ form adjacency Full với DR và BDR
DRother-DRother: 2-Way state

Cấu hình DR

R1(config)# interface gi0/1
R1(config-if)# ip ospf priority 100
R1(config-if)# exit

# Non-preemptive: không tự động đổi DR
# Cần clear để bầu lại
R1# clear ip ospf process

Verify DR/BDR

R1# show ip ospf neighbor
# Output:
Neighbor ID     Pri   State           Dead Time   Address
2.2.2.2         1     2WAY/DROTHER    00:00:38    10.0.0.2
3.3.3.3         1     FULL/BDR        00:00:35    10.0.0.6
4.4.4.4         1     FULL/DR         00:00:32    10.0.0.10

Multi-Area OSPF

Cấu hình ABR

# ABR (Area Border Router)
ABR(config)# router ospf 1
ABR(config-router)# router-id 1.1.1.1
ABR(config-router)# network 192.168.1.0 0.0.0.255 area 1
ABR(config-router)# network 10.0.0.0 0.0.0.3 area 0
ABR(config-router)# exit

# Interface-level
ABR(config)# interface gi0/0
ABR(config-if)# ip ospf 1 area 0
ABR(config-if)# exit

ABR(config)# interface gi0/1
ABR(config-if)# ip ospf 1 area 1
ABR(config-if)# exit

Stub Area

# Trên tất cả routers trong stub area
R1(config)# router ospf 1
R1(config-router)# area 1 stub
R1(config-router)# exit

# Trên ABR
ABR(config)# router ospf 1
ABR(config-router)# area 1 stub
ABR(config-router)# exit

# Totally Stubby (Cisco)
ABR(config-router)# area 1 stub no-summary

NSSA (Not-So-Stubby Area)

R1(config)# router ospf 1
R1(config-router)# area 1 nssa
R1(config-router)# exit

# ABR
ABR(config)# router ospf 1
ABR(config-router)# area 1 nssa

Virtual Link

# Khi area không kết nối trực tiếp area 0
R1(config)# router ospf 1
R1(config-router)# area 1 virtual-link 2.2.2.2
R1(config-router)# exit

# Cả 2 đầu đều phải config
R2(config)# router ospf 1
R2(config-router)# area 1 virtual-link 1.1.1.1

OSPF Authentication

Type 1 - Plain text (không khuyến nghị)

R1(config)# interface gi0/1
R1(config-if)# ip ospf authentication
R1(config-if)# ip ospf authentication-key Cisco123

Type 2 - MD5

R1(config)# interface gi0/1
R1(config-if)# ip ospf authentication message-digest
R1(config-if)# ip ospf message-digest-key 1 md5 Cisco123

Type 3 - SHA (mới hơn)

R1(config)# interface gi0/1
R1(config-if)# ip ospf authentication key-chain MYKEY
R1(config-if)# exit

R1(config)# key chain MYKEY
R1(config-keychain)# key 1
R1(config-keychain-key)# key-string Cisco123
R1(config-keychain-key)# cryptographic-algorithm hmac-sha-256
R1(config-keychain-key)# exit
R1(config-keychain)# exit

OSPF Network Types

Broadcast (default cho Ethernet)

- DR/BDR election
- Multicast 224.0.0.5, 224.0.0.6
- Hello 10s, Dead 40s
- Auto neighbor discovery

Point-to-Point

R1(config)# interface serial0/0
R1(config-if)# ip ospf network point-to-point

- Không DR/BDR
- Hello 10s, Dead 40s
- Auto neighbor discovery

Non-Broadcast (NBMA)

- DR/BDR election
- Unicast
- Hello 30s, Dead 120s
- Cần neighbor statement

Point-to-Multipoint

R1(config)# interface serial0/0
R1(config-if)# ip ospf network point-to-multipoint

- Không DR/BDR
- Hello 30s, Dead 120s
- Auto neighbor discovery

EIGRP

Overview

- Cisco proprietary (đã mở 2013)
- Advanced distance vector
- DUAL algorithm
- AD: 90 (internal), 170 (external)
- Multicast: 224.0.0.10
- Protocol number: 88

Cấu hình cơ bản

R1(config)# router eigrp 100
R1(config-router)# no auto-summary
R1(config-router)# network 192.168.1.0 0.0.0.255
R1(config-router)# network 10.0.0.0 0.0.0.3
R1(config-router)# exit

# Với passive interface
R1(config-router)# passive-interface gi0/1
R1(config-router)# exit

# Verify
R1# show ip eigrp neighbors
R1# show ip eigrp topology
R1# show ip route eigrp
R1# show ip protocols

EIGRP Metrics

Composite metric:
- Bandwidth (K1)
- Delay (K3)
- Load (K2)
- Reliability (K4, K5)

Default: BW + Delay
Formula: 256 × (10^7/min_BW + sum_delay/10)

Bài tập thực hành

Hãy cấu hình OSPF multi-area!