From: Daniel Free (danrose111@earthlink.net)
Date: Fri Apr 25 2003 - 17:31:38 GMT-3
Hi Jim,
I just finished doing your scenario on my lab.
You are 100 % correct. Very sorry for my initial
response to this question. This will teach me to be
sure before I answer. I made R1,R2,R3,R4,R5
ethernets in area 1. I added Area 0 to R1 and R2.
I added Area 3 to R3, Area 4 to R4 and Area 5 to
R5. R1 was the DR, R2 was DRother, R3 was DRother, R4 was DRother. R5 was
BDR. I had absolutely no problem establishing virtuals links
from R3,R4 and R5 to R2. For fun I established R3
and R4 virtual links to R2 and R5 virtual link to R1.
So you are correct in the fact that in this scenario
it will work because virtual-links are using router id's. If this was a
production environment you would
also want to establish dual virtual-links. One from
R3,R4 and R5 to R1 and one from R3,R4 and R5
to R2 for redundancy purposes. It's been fun. Best of luck.
Danny
----- Original Message -----
From: "Daniel Free" <danrose111@earthlink.net>
To: "ccie2be" <ccie2be@nyc.rr.com>; "Jon CarMicheal"
<jonc@whirled-routers.com>; "Group Study" <ccielab@groupstudy.com>
Sent: Friday, April 25, 2003 4:20 AM
Subject: Re: OSPF virtual link in combo with ethernet
> Hi Jim,
> I will have to lab this and get back to you.
> Danny
> ----- Original Message -----
> From: "ccie2be" <ccie2be@nyc.rr.com>
> To: "Jon CarMicheal" <jonc@whirled-routers.com>; "Group Study"
> <ccielab@groupstudy.com>; "Daniel Free" <danrose111@earthlink.net>
> Sent: Thursday, April 24, 2003 7:49 PM
> Subject: Re: OSPF virtual link in combo with ethernet
>
>
> > Hey Danny and Jon,
> >
> > Thanks for getting back to me. I appreciate it.
> >
> > Although I accept what you're saying as true, it doesn't really make
sense
> > to me. Here's why.
> >
> > 1st of all, a virtual link is configured between router ID's so as to
> create
> > a tunnel between ABR's. And, nothing I've come across says that the
ABR's
> > have to be adjacent.
> >
> > 2nd, if the ABR's had to be adjacent, then it wouldn't be possible to
have
> a
> > virtual link between 2 ABR's that weren't directly connected as in
> >
> > non-backbone area --- R1--- transit area --- R2 --- transit area ---
> R3 ---
> > area0
> >
> > If ABR's had to be adjacent you couldn't have a virtual link between R1
> and
> > R3.
> >
> > Now consider this topology:
> >
> >
> > Area 0
> > | |
> > R1 R2
> > |-----|---------|--------| Ethernet segment with all interfaces in
> Area1
> > | | |
> > R3 R4 R5 where R4= BDR and R5=DR
> > | | |
> > A3 A4 A5 where A = area
> >
> >
> > In this topology, is it possible that a virtual link can't be created
> > between R3 and either R1 or R2? does that make sense?
> >
> > If you (or somebody else on Group STudy) could explain this to me, I'd
be
> > one happy camper. Thanks. Jim
> >
> >
> >
> > ----- Original Message -----
> > From: "Daniel Free" <danrose111@earthlink.net>
> > To: "ccie2be" <ccie2be@nyc.rr.com>; "Group Study"
<ccielab@groupstudy.com>
> > Sent: Thursday, April 24, 2003 5:40 PM
> > Subject: Re: OSPF virtual link in combo with ethernet
> >
> >
> > > Hi Jim,
> > > Your very last statement is correct. Just think of how OSPF works on a
> > > broadcast medium. There
> > > will be a DR/BDR election process. Each non DR/BDR router (DRother)
> forms
> > an
> > > adjacency with
> > > a DR and a BDR. In your sample you need to configure the virtual link
to
> > > Router A, in this case the BDR because it is attached to Area 0. Best
of
> > > luck.
> > > Danny
> > > ----- Original Message -----
> > > From: "ccie2be" <ccie2be@nyc.rr.com>
> > > To: "Group Study" <ccielab@groupstudy.com>
> > > Sent: Thursday, April 24, 2003 3:47 PM
> > > Subject: OSPF virtual link in combo with ethernet
> > >
> > >
> > > > Hi group,
> > > >
> > > > I have 4 routers, A, B, C and D on an ethernet segment with each
> > router's
> > > > ethernet interface configured to be in OSPF area 1. Routers A and B
> are
> > > ABRs
> > > > between area 0 and area 1. Router C is also an ABR between area 1
and
> > > area
> > > > 2.
> > > >
> > > > When I configured a virtual link between rtr C and B it doesn't
work -
> > the
> > > > output of show ip ospf virtual-link shows the v-link down. However,
> > when
> > > I
> > > > configure the v-link between rtr C and A, it does work. I'm trying
to
> > > figure
> > > > out why this is.
> > > >
> > > > On rtr C, I did a show ip ospf nei and saw the following:
> > > >
> > > > nei A Full/BDR
> > > > nei B 2way/DRother
> > > > nei D Full/DR
> > > >
> > > >
> > > > Also, when I ping trace between rtr C and B, it takes 2 hops, not 1
> even
> > > > though both rtr C and B are on the same ethernet segment.
> > > >
> > > > Given the above info, is it possible that a virtual link across an
> > > ethernet
> > > > segment has to be between a router and the DR or BDR on the segment?
> > > >
> > > > Thanks in advanced. Jim
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