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A question about ospf

 
 
aaabbb16@hotmail.com
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      08-05-2007
If there are only two routers on the broadcast neighborship.
Is it point to point? Does it still select DR and BDR? if not,
does it work like point --point (non broadcast neighborship)?

TIA,
/st

 
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Gabriele Beltrame
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      08-05-2007
<(E-Mail Removed)> ha scritto nel messaggio
news:(E-Mail Removed) oups.com...
> If there are only two routers on the broadcast neighborship.
> Is it point to point? Does it still select DR and BDR? if not,
> does it work like point --point (non broadcast neighborship)?
>
> TIA,
> /st


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


 
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Merv
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      08-05-2007
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.




 
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aaabbb16@hotmail.com
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      08-05-2007
On 8 5 , 5 29 , "Gabriele Beltrame" <(E-Mail Removed)> wrote:
> <(E-Mail Removed)> ha scritto nel messaggionews:1186290911.205809.172200@d30g2000prg .googlegroups.com...
>
> > If there are only two routers on the broadcast neighborship.
> > Is it point to point? Does it still select DR and BDR? if not,
> > does it work like point --point (non broadcast neighborship)?

>
> > TIA,
> > /st

>
> 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


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.

Second question is that all relate to OSPF packets use multicast
(224...5 and 224...6). Is it true? because from this URL (http://
http://www.netacad.lania.mx/reetolin...t#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?

TINA,
/st

 
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Gabriele Beltrame
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      08-05-2007
<(E-Mail Removed)> ha scritto nel messaggio
news:(E-Mail Removed) oups.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 --
>>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://
> http://www.netacad.lania.mx/reetolin...t#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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stephen
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      08-05-2007
<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> On 8 5 , 5 29 , "Gabriele Beltrame" <(E-Mail Removed)> wrote:
> > <(E-Mail Removed)> ha scritto nel

messaggionews:1186290911.205809.172200@d30g2000prg .googlegroups.com...
> >
> > > If there are only two routers on the broadcast neighborship.
> > > Is it point to point? Does it still select DR and BDR? if not,
> > > does it work like point --point (non broadcast neighborship)?

> >
> > > TIA,
> > > /st

> >
> > 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

>
> 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?


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
> 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 (http://
> http://www.netacad.lania.mx/reetolin...t#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?


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.....
>
> TINA,
> /st

--
Regards

http://www.velocityreviews.com/forums/(E-Mail Removed) - replace xyz with ntl


 
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