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| 2.2. OSPF
type of packets |
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| OSPF runs directly over IP using
protocol number 89. OSPF packets should always be sent with
the IP TOS field set to 0. If at all possible, OSPF
packets should be given preference over regular IP traffic,
both when being sent and received. (As an aid, OSPF packets should
have their IP precedence field set to Internetwork Control). |
| All OSPF packets share a common protocol
header. Every OSPF packet starts with a standard 24 byte header.
This header contains all the information necessary to determine whether the
packet should be accepted for further processing. Field of the header
are showed in the next figure. |
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| The OSPF packet types are: |
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| OSPF uses Hello packets to
discover and maintain neighbor relationships. Database Description (DDP)
and Link State Request packets are used in the forming of
adjacencies. OSPF's reliable update mechanism is implemented by
Link State Update and Link State Ack packets. |
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| Each Link State Update packet carries a
set of new Link State Advertisements (LSAs) one hop further
away from their point of origination. The different types of OSPF LSAs
are listed below: |
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| OSPF routing packet (except Hello)
are sent only over adjacencies. This means that all OSPF packets
travel a single IP hop, except those sent over virtual adjacencies.
The IP source address is one end of a router adjacency and the IP
destination address is either the other end of the adjancency or an
IP multicast address. |
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