From: Daniel Free (danrose111@earthlink.net)
Date: Fri Apr 25 2003 - 05:20:41 GMT-3
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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