The standard procedure when receiving a valid LSA is to retransmit that LSA
out a set of interfaces. However, section 13.3 of RFC 2328 describes a list
of numerous caveats. One of those is that should you receive an LSA that in
all probability was successfully received by other routers out a particular
interface, there is no need to retransmit it. This applies particularly
when you are not the DR or BDR and you receive an LSA from the DR. The
standardized procedure is not to retransmit that LSA out the receiving
interface. However, that LSA is retransmitted out of all other interfaces
that do not conflict the with noted caveats in 13.3.
As far as examples go, the DR sends to the rest of the broadcast segment as
it is adjacent to all. Each of those routers in turn flood out whatever
other transit interfaces they possess excluding the one where the LSA was
received.
Does that help?
Pete
*********** REPLY SEPARATOR ***********
On 7/3/2001 at 9:42 AM Ole Drews Jensen wrote:
>> I am currently reading the CiscoPress BSCN book, and I find myself a bit
>> confused on the LSU/LSA procedures in OSPF.
>>
>> When many routers are connected on the same LAN segment, and are
>therefore
>> neighbors to eachother, a DR and a BDR will be elected.
>>
>> First they write that routers do not flood OSPF updates/advertisements to
>> all the OSPF routers (224.0.0.5), but only to the DR OSPF routers
>> (224.0.0.6). It is then the task of the DR(s) to flood whatever needs to
>> be flooded to all the routers.
>>
>> However, a little later in the book, they tell me that when a router
>> receives an update from a DR router, it will flood it to all routers.
>>
>> They also write that when a router receives an update, it will flood it
>to
>> all DR OSPF routers on other connected LAN segments.
>>
>> Can someone give me a simple explanation on who sends what to where?
>>
>> Thanks in advance,
>>
>> Ole
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> Ole Drews Jensen
>> Systems Network Manager
>> CCNA, MCSE, MCP+I
>> RWR Enterprises, Inc.
>> [EMAIL PROTECTED]
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> http://www.OleDrews.com/CCNP
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> NEED A JOB ???
>> http://www.oledrews.com/job
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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http://www.groupstudy.com/form/read.php?f=7&i=10875&t=10803
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