A question about ospf

ha scritto nel messaggio news: snipped-for-privacy@d30g2000prg.googlegroups.com...

Hi,

It is always "broadcast" by default and "works" as such, so there is DR/BDR election and Type2 LSAs. Since this is a waste of LSA database resources, you can force OSPF to treat the link as Point-to-Point.

Regards, Gabriele

Also the adjacency will take longer to form than necessary as there is a 40 second wait time on braodcast media to ensure that all routers that could become DR or BDR are detected.

messaggionews: snipped-for-privacy@d30g2000prg.googlegroups.com...

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 --

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.

Second question is that all relate to OSPF packets use multicast (224...5 and 224...6). Is it true? because from this URL

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?

TINA, /st

ha scritto nel messaggio news: snipped-for-privacy@z24g2000prh.googlegroups.com...

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)

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)

Regards, Gabriele

messaggionews: snipped-for-privacy@d30g2000prg.googlegroups.com...

this isnt part of the exchange as such, it happens when "hello" 1st starts on 1 of the routers.

once 1 of them "elects" itself (since both are unlikely to start the interface simultaneously), it stays that way as the election result is sticky, and the elected interface needs to go down to force another.

the only case where election may start when an adjacency is coming up is when you have a LAN with a break in it, and the 2 interfaces are on different sides - the 2 routers both get an interface elected, and you have a resolution to fix that.

(exstart decide who is master/slave, means master start to

the gold rule with RFCs is "check the source".

RFC 2328 is the standard and it is fairly clearly written - so check that.

if you must use a book, then "John Moy - Anatomy of a routing protocol" is now pretty old, but the author was involved in producing the protocol.....