[c-nsp] OSPF router gets separated from a broadcast domain

[Whisper]

Either I am mis-reading what you are trying to ask, or you are not making
yourself very clear, because what I can gather from your descriptions thus
far, this is explicitly covered in most OSPF explanations.

This may help you understand things more clearly.

Routers don't become DR/BDR/DROthers, it is Router Interfaces.

Thus a router can have an Interface that is operating as a DR in 1 network
and as a BDR/DROther in another network

This answer is all based on the assumption that I've understood what you are
trying to ask.

Hope that helps

On Jan 29, 2008 10:30 PM, Gabor Ivanszky <ivanszky at niif.hu> wrote:

> Enno Rey wrote:
> >
> >> Now one of the routers gets separated from the network, while it's
> >> physical interface remains in "up" state, which is easily possible
> >> especially with ethernet. Now the routers can not see each other, so
> >> both of them became DR, and start to announce the network. The problem
> >> is with the announcement of the separated router, which could
> >> potentially create a black-hole in the network.
> >>
> >
> > hmm... maybe I do not get your scenario here... but if that router "gets
> separated" (whatever action you refer to here in detail, especially with its
> interface staying "up")... how can it still announce anything to the network
> it just got separated from?
> >
> > What kind of "separation" do you mean?
> >
> >
> >
> I try to describe it with a simplistic scenario:
> you have a L2 network made up of two ethernet switches(SWITCH A and
> SWITCH B). You have hosts, servers, etc. and OSPF ROUTER A connected
> directly to SWITCH A, and you have OSPF ROUTER B connected to SWITCH B.
> You have SWITCH A and SWITCH B connected with a link. All L3 interfaces
> connected to this L2 broadcast domain share the same prefix: NET X.
> ROUTER A & ROUTER B have their own uplinks to the backbone, making NET
> X  reachability redundant. Now everything works as expected.
>
> At some point in time the link between SWITCH A and SWITCH B breaks
> down.  Now you have ROUTER B(and SWITCH B of course) separated from the
> other parts(hosts, servers, ROUTER A) of NET X. Since ROUTER B still has
> it's interface "up", and it is configured with an IP address from NET X,
> it continues to announce NET X. If this announcement is more
> attractive(in terms of OSPF metrics) than the similar announcement made
> by ROUTER A, then the traffic destined to NET X will flow to ROUTER B,
> and become blackholed.
>
> I hope I made the issue clearer. ;)
>
> regards,
> Gabor
>
> _______________________________________________
> cisco-nsp mailing list  cisco-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-nsp
> archive at http://puck.nether.net/pipermail/cisco-nsp/
>