From: ccie2be (ccie2be@nyc.rr.com)
Date: Thu Apr 24 2003 - 20:49:36 GMT-3
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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