Subject: OSPF Question

From: Vinay Ravuri <[email-masked]>
Date: Mon, 21 Oct 2002 10:57:58 -0700

Hi,

   Consider the following topology.

    A --------B----------C
    |         |             |
    |         |             |
    D        E          F

Where A, B, C, D, E, F are routers and A, B, C have interfaces out to each other and to D, E, F respectivley.

If I wanted to keep the interfaces between A, B, C private to routers A, B, C.  That is, I do not want D, E, F to know about the interfaces that exist between A, B, C but still have D, E, F to reach each other some how.  How could I accomplish this with OSPF?

One thought I had was perhaps run 2 instances of OSPF on A, B, C.  First instance runs between iterfaces on A, B, C and second between A->D, B->E, C->F and advertise the reachability to D, E, F via the interfaces A, B, C and keep the interfaces between A, B, C hidden.  Does doing something like this make sense or is there a better to accomplish this.  Also, with OSPF how does one differentiate between interfaces on a another node inorder to selectively leak routes?

-Vinay

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From: Sina Mirtorabi <[email-masked]>
Date: Mon, 21 Oct 2002 15:21:12 -0700

Vinay

by " not knowing about interface that exist" , do you mean topology wise or
even not knowing IP reachability regarding those interface ?

some option that you have depending on what really you are looking for ....

a) make link A-B & B-C in area 0 and each other link in a different area

if you don't want IP information of A-B and B-C to be advertised you can

b) filter on A / B / C the corresponding prefixes belonging to area 0 (
given that you can do type 3 filtering )
c) make the non-backbone areas totally stub in order to just have a default
route on D, E, F

d) run different process and redistribute as you pointed out but it can be
tricky if there are some back door link between D/E/F

Sina
  -----Original Message-----
  From: Mailing List [mailto:[email-masked]]On Behalf Of Vinay
Ravuri
  Sent: Monday, October 21, 2002 10:58 AM
  To: [email-masked]
  Subject: OSPF Question

  Hi,

      A --------B----------C
      |         |             |
      |         |             |
      D        E          F

  Where A, B, C, D, E, F are routers and A, B, C have interfaces out to each
other and to D, E, F respectivley.

  If I wanted to keep the interfaces between A, B, C private to routers A,
B, C.  That is, I do not want D, E, F to know about the interfaces that
exist between A, B, C but still have D, E, F to reach each other some how.
How could I accomplish this with OSPF?

  One thought I had was perhaps run 2 instances of OSPF on A, B, C.  First
instance runs between iterfaces on A, B, C and second between A->D, B->E,
C->F and advertise the reachability to D, E, F via the interfaces A, B, C
and keep the interfaces between A, B, C hidden.  Does doing something like
this make sense or is there a better to accomplish this.  Also, with OSPF
how does one differentiate between interfaces on a another node inorder to
selectively leak routes?

  -Vinay

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From: Vinay Ravuri <[email-masked]>
Date: Mon, 21 Oct 2002 18:00:37 -0700

Sina,
     Thanks you for your reply.  I do not want IP reachability between A-B, B-C to be advertised to anyone outside of A, B, C.
Your b),  is the stub area between A-B, B-C links and advertise default routes out on A-D, B-E, C-F links to reach A, B, C?  If so, I think this approach should work.
Your c), there will likely be links between D, E, F - Where do you see a problem here?  If I am only advertising reachability to A, B, C on A-D, B-E, C-F links.
-Viinay
 Sina Mirtorabi <[email-masked]> wrote:Vinay by " not knowing about interface that exist" , do you mean topology wise or even not knowing IP reachability regarding those interface ? some option that you have depending on what really you are looking for .... a) make link A-B & B-C in area 0 and each other link in a different area if you don't want IP information of A-B and B-C to be advertised you can b) filter on A / B / C the corresponding prefixes belonging to area 0 ( given that you can do type 3 filtering )c) make the non-backbone areas totally stub in order to just have a default route on D, E, F d) run different process and redistribute as you pointed out but it can be tricky if there are some back door link between D/E/F Sina-----Original Message-----
From: Mailing List [mailto:[email-masked]]On Behalf Of Vinay Ravuri
Sent: Monday, October 21, 2002 10:58 AM
To: [email-masked]
Subject: OSPF Question

Hi,

    A --------B----------C
    |         |             |
    |         |             |
    D        E          F

-Vinay

---

From: Sina Mirtorabi <[email-masked]>
Date: Mon, 21 Oct 2002 20:00:11 -0700

Vinay

Vinay> Your b),  is the stub area between A-B, B-C links and advertise
default routes out on A-D, B-E, C-F links to reach A, B, C?
Vinay> If so, I think this approach should work.

I guess you mean c) and not b) , yes totally stub will satisfy your
requirement ....

Vinay> Your c), there will likely be links between D, E, F - Where do you
see a problem here?
Vinay> If I am only advertising reachability to A, B, C on A-D, B-E, C-F
links

you mean d) and not c),  if there is a backdoor and D/E/F can exchange
reachability without going through A/B/C then you do not need any
redistribution.

I don't know exactly your topology / requirement but if you are
redistributing between multiple process in more than one point you need to
be careful, I can send you a paper that I wrote on that....

Sina
   Sina Mirtorabi <[email-masked]> wrote:

    Vinay

    by " not knowing about interface that exist" , do you mean topology wise
or even not knowing IP reachability regarding those interface ?

    some option that you have depending on what really you are looking for
....

    b) filter on A / B / C the corresponding prefixes belonging to area 0
( given that you can do type 3 filtering )
    c) make the non-backbone areas totally stub in order to just have a
default route on D, E, F

    d) run different process and redistribute as you pointed out but it can
be tricky if there are some back door link between D/E/F

    Sina
      -----Original Message-----
      From: Mailing List [mailto:[email-masked]]On Behalf Of
Vinay Ravuri
      Sent: Monday, October 21, 2002 10:58 AM
      To: [email-masked]
      Subject: OSPF Question

      Hi,

          A --------B----------C
          |         |             |
          |         |             |
          D        E          F

      Where A, B, C, D, E, F are routers and A, B, C have interfaces out to
each other and to D, E, F respectivley.

      If I wanted to keep the interfaces between A, B, C private to routers
A, B, C.  That is, I do not want D, E, F to know about the interfaces that
exist between A, B, C but still have D, E, F to reach each other some how.
How could I accomplish this with OSPF?

      One thought I had was perhaps run 2 instances of OSPF on A, B, C.
First instance runs between iterfaces on A, B, C and second between A->D,
B->E, C->F and advertise the reachability to D, E, F via the interfaces A,
B, C and keep the interfaces between A, B, C hidden.  Does doing something
like this make sense or is there a better to accomplish this.  Also, with
OSPF how does one differentiate between interfaces on a another node inorder
to selectively leak routes?

      -Vinay

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      Y! Web Hosting - Let the expert host your web site

---

From: Vinay Ravuri <[email-masked]>
Date: Wed, 23 Oct 2002 09:42:20 -0700

Sina,
       I would be interested in reading your paper.  Please send it to [email-masked]
Cheer,
Vinay
 Sina Mirtorabi <[email-masked]> wrote:Vinay Vinay> Your b),  is the stub area between A-B, B-C links and advertise default routes out on A-D, B-E, C-F links to reach A, B, C?  Vinay> If so, I think this approach should work.  I guess you mean c) and not b) , yes totally stub will satisfy your requirement .... Vinay> Your c), there will likely be links between D, E, F - Where do you see a problem here? Vinay> If I am only advertising reachability to A, B, C on A-D, B-E, C-F links you mean d) and not c),  if there is a backdoor and D/E/F can exchange reachability without going through A/B/C then you do not need any redistribution. I don't know exactly your topology / requirement but if you are redistributing between multiple process in more than one point you need to be careful, I can send you a paper that I wrote on that.... Sina
 Sina Mirtorabi <[email-masked]> wrote: Vinay by " not knowing about interface that exist" , do you mean topology wise or even not knowing IP reachability regarding those interface ? some option that you have depending on what really you are looking for .... a) make link A-B & B-C in area 0 and each other link in a different area if you don't want IP information of A-B and B-C to be advertised you can b) filter on A / B / C the corresponding prefixes belonging to area 0 ( given that you can do type 3 filtering )c) make the non-backbone areas totally stub in order to just have a default route on D, E, F d) run different process and redistribute as you pointed out but it can be tricky if there are some back door link between D/E/F Sina-----Original Message-----
From: Mailing List [mailto:[email-masked]]On Behalf Of Vinay Ravuri
Sent: Monday, October 21, 2002 10:58 AM
To: [email-masked]
Subject: OSPF Question

Hi,

    A --------B----------C
    |         |             |
    |         |             |
    D        E          F

-Vinay