3com 5500-ei pwr Instrução De Instalação

 

4-3 

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Hello packet: 

Hello packets are most commonly used OSPF packets, which are periodically sent by a router to its 

neighbors. A Hello packet contains the values of some timers, DR, BDR and known neighbors. 

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DD packet: 

When two routers synchronize their databases, they use database description (DD) packets to describe 

their own LSDBs, including the summary of each LSA. The summary refers to the header of an LSA 

which uniquely identifies the LSA. This reduces the size of traffic transmitted between the routers 

because the header of an LSA only occupies a small portion of the LSA. With the header, the peer 

router can judge whether it has the LSA or not. 

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LSR packet: 

After exchanging DD packets, the two routers know which LSAs of the peer router are lacked in the local 

LSDB, and send link state request (LSR) packets requesting for the lacked LSAs to the peer. These 

LSR packets contain the digest of the needed LSAs. 

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LSU packet: 

Link state update (LSU) packets are used to transmit the needed LSAs to the peer router. An LSU 

packet is a collection of multiple LSAs (complete LSAs, not LSA digest). 

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LSAck packet 

Link state acknowledgment (LSAck) packets are used to acknowledge received LSU packets. An 

LSAck contains the header(s) of LSA(s) to be acknowledged (One LSAck packet can acknowledge 

multiple LSAs). 

1)  Five basic LSA types 

As described in the preceding sections, LSAs are the primary source for OSPF to calculate and 

maintain routes. RFC 2328 defines five types of LSAs: 

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Router-LSA: Type-1 LSAs, generated by every router to describe the router's link states and costs, 

and advertised only in the originating area. 

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Network-LSA: Type-2 LSAs, generated by the DRs on a broadcast or NBMA network to describe 

the link states of the current network segment, and are advertised only in the originating area. 

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Summary-LSA: Type-3 and Type-4 LSAs, generated by ABRs and advertised in the areas 

associated with the LSAs. Each Summary-LSA describes a route to a destination in another area of 

the AS (also called inter-area route).Type-3 Summary-LSAs are for routes to networks (that is, their 

destinations are segments), while Type-4 Summary-LSAs are for routes to ASBRs. 

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AS-external-LSA: Type-5 LSA, also called ASE LSA, generated by ASBRs to describe the routes 

to other ASs and advertised to the whole AS (excluding stub areas and NSSA areas). The default 

AS route can also be described by AS-external-LSAs. 

2) Type-7 

LSAs 

In RFC 1587 (OSPF NSSA Option), Type-7 LSA, a new LSA type, is added. 

As described in RFC 1587, Type-7 LSAs and Type-5 LSAs mainly differ in the following two ways: 

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Type-7 LSAs are generated and advertised in an NSSA, where Type-5 LSAs will not be generated 

or advertised.