OSPF - Routing Protocols and Concepts - page 498

OSPF Concepts Exercise

Background of OSPF

The initial development of OSPF began in 1987 by the Internet Engineering Task Force ( IETF ) OSPF
Working Group. At that time, the Internet was largely an academic and research network funded by
the U.S. government.

In 1998, the OSPFv2 specification was updated to the current version reflected in RFC 2328 . Because
OSPF is an open standard, you can easily find the RFC online. List one website where the OSPF RFC
can be found:

http://www.ietf.org/rfc/rfc2328

OSPF Message Encapsulation

The data portion of an OSPF message is encapsulated in a packet. This data field can include one of
five OSPF packet types. Each packet type is briefly discussed in the next topic.

Figure 11-1 shows an example of an encapsulated OSPF message. Fill in the missing field contents.

Figure 11-1 Encapsulated OSPF Message (Answer)

Data Link Frame
Header

IP Packet
Header

OSPF Packet
Header

OSPF Packet
Type-Specific Data

Data Link Frame (Ethernet Fields Shown Here)
MAC Source Address = Address of Sending Interface
MAC Destination Address = Multicast: 01-00-5E-00-00-05 or 01-00-5E-00-00-06

IP Packet
IP Source Address = Address of Sending Interface
IP Destination Address = Multicast: 224.0.0.5 or 224.0.0.6
Protocol Field = 89 for OSPF

OSPF Packet Header
Type Code for OSPF Packet Type
Router ID and Area ID

OSPF Packet Types
0x01 Hello
0x02 Database Description (DD)
0x03 Link State Request
0x04 Link State Update
0x05 Link State Acknowledgment

OSPF Packet Types

The following list describes the five different types of OSPF link-state packets (LSP). Each packet
serves a specific purpose in the OSPF routing process. Fill in the name for each packet type.

Hello : Used to establish and maintain adjacency with other OSPF routers

1.

Database description ( DBD ): Contains an abbreviated list of the sending router's link-state
database and is used by receiving routers to check against the local link-state database

2.

Link - state request ( LSR ): A request for more information about an entry in the DBD 3.

Link - state update ( LSU ): Used to reply to LSRs as well as to announce new information

4.

Link - state acknowledgment ( LSAck ): Confirms receipt of an LSU 5.