Buno

OSPF

PART 1

packetlife.net

Protocol Header
8

Attributes

16

Version

24

Type

32

Type Link-State

Length

Algorithm Dijkstra

Router ID

Metric Cost (Bandwidth)Area ID
Checksum

AD 110

Instance ID

Reserved

Standard RFC 2328, 2740

Data

Protocols IP

Link State Advertisements
Router Link (Type 1)
Lists neighboring routers and the cost toeach; flooded within an area
Network Link (Type 2)
Generated by a DR; lists all routers on an adjacent segment; flooded
within an area

Transport IP/89
Authentication Plaintext, MD5
AllSPFAddress 224.0.0.5
AllDR Address 224.0.0.6
Metric Formula
100,000 Kbps*

Network Summary (Type 3)
Generated by an ABR and advertised among areas

cost =

ASBR Summary (Type 4)
Injected by anABR into the backbone to advertise the presence of an
ASBR within an area

* modifiable with
ospf auto-cost reference-bandwidth

External Link (Type 5)
Generated by an ASBR and flooded throughoutthe 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
Router TypesArea Types

Internal Router
All interfaces reside within the
same area
Backbone Router
A router with an interface in
area 0 (the backbone)

Standard Area
Default OSPF area type
Stub AreaExternal link (type 5) LSAs are
replaced with a default route

Area Border Router (ABR)
Connects two or more areas

Totally Stubby Area
Type 3, 4, and 5 LSAs are
replaced with a default routeAS Boundary Router (ASBR)
Connects to additional routing
domains; typically located in
the backbone

Not So Stubby Area (NSSA)
A stub area containing an ASBR;
type 5 LSAs are converted totype
7 within the area

link speed

Adjacency States
1 Down

5 Exstart

2 Attempt

6 Exchange

3 Init

7 Loading

4 2-Way

8 Full
DR/BDR Election

The DR serves as a common...