OSPF Overview

Type Link-State
Algorithm Dijkstra
Metric Cost (Bandwidth)
AD 110
Standard RFC 2328, 2740
Protocols IP
Transport IP/89
Authentication Plaintext, MD5
AllSPF Address 224.0.0.5
AllDR Address 224.0.0.6

Возможное кол-во роутеров – не больше 50 для одной зоны

To form adjacency need neighbours must agree on :

• Unique Router-ID
• Unique IP Address
• Interface Area ID
• Hello interval & Dead Interval
• Interface network address
• Interface MTU
• Network Type
• Authentication
• Stub flags
• Other optional capabilities

Link State Advertisements

Router Link (Type 1)
Lists neighboring routers and the cost to each; flooded within an area
Network Link (Type 2)
Generated by a DR; lists all routers on an adjacent segment; flooded within an area
Network Summary (Type 3)
Generated by an ABR and advertised among areas
ASBR Summary (Type 4)
Injected by an ABR into the backbone to advertise the presence of an ASBR within an area
External Link (Type 5)
Generated by an ASBR and flooded throughout the AS to advertise a route external to OSPF
NSSA External Link (Type 7)
Generated by an ASBR in a not-so-stubby area; converted into a type 5 LSA by the ABR when leaving the area

OSPF messages types:

Hello пакет содержит следующие поля для выбора DR/BDR:

• Designated Router
• Backup Designated Router
• Router Priority

DR – чем выше приоритет, router-id
Если приоритет равен нулю, то роутер не участвует в выборах DR/BDR.

OSPF Neighbor States:

• Down – shutdown interface
• Init – Hello packet received
• 2-Way – Own router-ID in received hello
• ExStart – Master and slave role determined
• Exchange  – Database description packets sent
• Loading. –  Exchange of LSR and LSU
• Full  –  Ful adjacent