TP-Link T3700G-28TQ User Manual page 200

6. LSAck Packet
When receiving a LSU, the router will send to the router forwarding the LSU packet a LSAck
packet including the LSA header it receives to confirm whether the data received is correct.
7. LSA
OSPF protocol defines area and multiple router types. Via various sorts of LSA, different types of
router complete routing update caused by network changes. OSPF protocol defines 11 types of
LSA, which all have the same LSA header. As shown below, every LSA is unique in the network,
and could be identified uniquely by the key field of LSA header.
1) Age: The time passed since the LSA is generated. When the age goes over the threshold
value set by the router system, which is one hour, and the router doesn't receive an LSA
update, it will delete this LSA.
2) Type: The type of LSA. Table 10-5 enumerates several common features of LSA.
3) Link State ID: It has different meanings for different types of LSA. For details please refer to
the RFC documentation.
4) Advertising Router: ID of the router advertising this LSA.
5) Sequence Number: It indicates the uniqueness of a certain LSA, whose update would be
flooded to the network by adding 1 to the sequence number.
In the table below are the features of 6 types of common LSA.
Type Name
Code
1 Router LSA
2 Network LSA
3 Network
Summary LSA
4 ASBR
Summary LSA
5 AS
LSA
Figure 10-44 LSA Header
Features
Originates from all the routers, and describes the router
interface which itself has already run the OSPF features and
then spreads in its advertising area.
Originates from DR, and describes the link state of all routers in
its connected network segment and then diffuses in its
advertising area.
Originates from ABR, and describes the routers of all segments
in the area and then advertises to the backbone area, the
routers in which area will re-summarize and then announce to
the other area.
Originates from ABR, and describes the routers from ABR to
ASBR and advertises the path to ASBR to the area ABR
connects.
Originates from ASBR, and describes the external route and the
External
accessible network obtained by other routing protocols. This
type of LSA will be flooded to the entire autonomous system.
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