Sina!
I have some more questions on u r clarifications. I have listed it below.
Can u pl. answer those?
  -----Original Message-----
  From: Mailing List [mailto:OSPFdiscuss.microsoft.com]On Behalf Of Sina
Mirtorabi
  Sent: Wednesday, July 04, 2001 4:11 AM
  To: OSPFdiscuss.microsoft.com
  Subject: Re: Doubt in Virtual Link

  Subrat
  actually there is a virtual link between R10 and R11 in order to link the
area 3 to the backbone
  if the link between R6-R10 goes down R10 won't be ABR any more and area 3
will be disconnected from the backbone
  [Subrat Mohanty] Even if u have a virtual link between R10 and R7, can I
say that Area 3 is connected to BB as there is an virtual link between
R11-R10 and R10-R7 and R7 is connected to BB? The basic condition for
establishing a virtual link is the routers should be ABR. if the link
between R6-R10 goes down R10 won't be ABR. Should the virtual link still
exist?
  here is another example

                         R2
                      / \
              / \
      / \
  R1--------------------------R3
  | |
  | |
  | |
  R5 R4

  R1-R5 is in area 1
  R1-R3 area 0
  R3-R4 area 2
  R1,R2,R3 area 3

  if the backbone link between R1-R3 is broken you need a virtual link
through R2 in order to maintain the connectivity
  [Subrat Mohanty] From the above scenario, I feel tha R1 and R3 are
connected to a common network (assuming that it's a LAN). When u say that BB
connectivity, does it mean that all the networks in the BB area, should be
connected physically via some router or the other? If that is the case, I
can conclude that the Topology of a OSPF network should be such that atleast
networks in BB will be connected. if the backbone link between R1-R3 is
broken , then I can still forward the data traffic thru R2 without having a
virtual link. Because R1 and R3 already would have the reachability info
between them. Then what is the extra benifit I have having a virtual link?

   virtual link could also be used in order to have control over the traffic
as intra area path are always preferred over Inter area path by playing with
virtual link you could make the traffic go through the desired path
  [Subrat Mohanty] Can u pl. give me an example of it? Or refer to any doc
where I will have the example?

  Sina

  Subrat Mohanty wrote:

    I have a basic doubt in Virtual Link. I am still not clear about the use
or
    benifit of the VLink.
    Pl. Check RFC-2328 Fig-6. Sec-3.4. See the last line which states

    "Note that a failure of the line between Routers RT6 and RT10 will cause
the
    backbone to become disconnected. Configuring a virtual link between
Routers
    RT7 and RT10 will give the backbone more connectivity and more
resistance to
    such failures. "

    Anyway RT7 and RT10 are connected thru network-6 and all the routers are
    having this info so that when the link fails between RT6-RT10 fails they
can
    still do the routing. What is the benifit of the Vlink?

    Can u pl. give me a scenario where I will have an advantage of a VLink?

    Regards Subrat

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