Re: A question about ospf

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news:1186332072.039686.208470@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Thanks Gabriele and Merv.
Some books and Cisco training books usually use two routers to explain
OSPF from powerup state to full state and not mention it is point to
point or broadcast. e.g. down-->init->exstart-->exchange state --
loading state-->
full state. if it is broadcast neighbors,which state for dr/bdr
selection? (exstart decide who is master/slave, means master start to
excange DBD first )
or it is true for any neighborships.

Database sync always uses master/slave relationship, either on
multi-access and point-to-point networks
DR might happen to be the master but it is not a must.

The DR election happens between after the routers have become adjacent
(2way just after init) but before the begin the exstart phase (of course)


Second question is that all relate to OSPF packets use multicast
(224...5 and 224...6). Is it true? because from this URL (http://
www.netacad.lania.mx/reetoling/OSPF_single_area.ppt#435,13,Hello
Protocol exchange process) "step4 Routers send unicast reply hello
packets
back router A with their own information" Is it only unicast packets
for all OSPF
related?

hello packets are multicasted to 224.0.0.5 on all broadcast capable
media (Broadcast,Point-to-point,point-to-multipoint)
hello packets are unicasted on non broadcast capable media (NBMA and
point-to-multipoint Non Broadcast) (you need to statically configure
neighbors)

LSA acks can be either multicasted or unicasted (e.g. delayed acks and
direct acks; it depends on medium of course)
LSA Updates too can be either multicasted or not. (DR always multicast
to 224.0.0.5 and others (including BDR) always multicast to 224.0.0.6)

TINA,
/st

Regards,
Gabriele


.

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