From: Narbik Kocharians (narbikk@gmail.com)
Date: Mon Nov 05 2007 - 20:27:47 ART
Can we set the network type of the spokes to P2P and the hub site to
Broadcast. Next we have to set the timers to match, that way the
routers will go into full state but they won't exchange any routes,
then you would configure a GRE tunnel to resolve the networks. This
way the hub will always be the DR.
That's if i am reading the requirements correctly.
On 11/5/07, Eric Phillips <ephillips@squick.cc> wrote:
>
> Very interesting solution Mark!
>
> I quickly labbed up a slightly similar situation, where R1 is the
> preferred
> DR, and R2 and R3 are on the same broadcast domain.
>
> I set the priority high on R1, and created an access list on R2 blocking
> traffic from R3, and an ACL on R3 blocking traffic from R2. What is
> astounding is R1 became the DR, and both R2 and R3 throught they were the
> BDR, and R1 was the DR. R1 thought R3 was the BDR, and R2 was the
> DROTHER.
>
> In this strange mismatched case, routing still worked! Routes were
> passed,
> a "debug ip ospf events" did not show any errors or anything odd.
>
> Then, even stranger, I cycled the OSPF process on R1, and now both R2 and
> R3
> thought THEY were the DR; and R1 picked R3 to be the DR. And still
> routing
> worked and debugs showed no error messages.
>
> So this didn't get what I wanted, but a very interesting find; I would
> have
> thought routers had to agree who was the DR/BDR.
>
> I will have to play with private VLANs a bit for sure, I didn't think
> about
> those at all.
>
> Thanks again!
>
> -Eric
>
>
> On 11/5/07, Mark Mahan <mmahan@caprock.com> wrote:
> >
> > I haven't set my home lab up for remote access yet so can't verify my
> > supposition. Since I'm supposing...
> >
> > If they are all connected to a switch, block direct multicast
> > communication between R2 and R3 using private VLANs and use local
> > proxy-arp at R1 for unicast communication between R2 and R3. OSPF
> > neighbor relationships will form between 1 and 2 and 1 and 3 and with
> > 1's priority set high then it will be the DR and if it dies then OSPF
> > dies but you are assured R1 being the DR when it comes back up. Be
> > great is node 1 was a routing switch and the other two were routers...
> >
> > I don't know if the DR would react to the R2 or R3 hello not showing the
> > other in the neighbor list.
> >
> >
> >
> >
> >
> > Mark Mahan
> > Network Engineer
> > -------------------------------
> > CapRock Communications
> > 4400 S. Sam Houston Parkway E.
> > Houston, Texas 77048
> > Office: 832 668 2528
> > mmahan@caprock.com
> > www.caprock.com
> >
> >
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> > -----Original Message-----
> >
> >
> > From: Mark Mahan
> > Sent: Monday, November 05, 2007 12:07 PM
> > To: Eric Phillips; ccielab@groupstudy.com
> > Subject: RE: Any way to force OSPF DR other than "priority 0"?
> >
> > If there is no restriction on setting network types, then what about
> > making the interfaces on the segment non-broadcast and setting the
> > neighbors' priorities to 0 with the neighbor command on the DR?
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > Eric Phillips
> > Sent: Monday, November 05, 2007 11:05 AM
> > To: ccielab@groupstudy.com
> > Subject: Any way to force OSPF DR other than "priority 0"?
> >
> > Hey all,
> >
> > I have done quite a bit of Googling and DOC-CD reading, and have not
> > found
> > anyone offering any clever ways to force the election of a certain
> > router as
> > the DR besides setting the priority to 0 on all other routers.
> >
> > For example, if I had a question that asked me to ensure Router1 was
> > always
> > the DR on a certain segment without touching the configuration of
> > Router2
> > and Router3 I can set the priority very high on Router1, but if Router1
> > boots a few seconds later than Router2, Router2 will be the DR even if
> > it
> > has it's default priority of 1. The only way I can think to completely
> > guarantee Router1 is always the DR is to make the priority 0 on all
> > other
> > routers.
> >
> > Am I missing something obvious, or am I over thinking this too much? I
> > have
> > not seen this asked in any practice labs, just theorizing what could
> > happen.
> >
> > -Eric
> >
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-- Narbik Kocharians CCIE# 12410 (R&S, SP, Security) CCSI# 30832 www.Net-WorkBooks.com
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