Subject: Hide a network between two routers

From: Markus Prison <[email-masked]>
Date: Fri, 26 Apr 2002 09:34:36 -0400

Hi people,

my question will be if it's possible to hide a network between two routers
for the routers that are connected to them within the ospf standard.

When it's not possible what do you suggest what changes i must do in my
ospf code of the two routers.

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From: Acee Lindem <[email-masked]>
Date: Fri, 26 Apr 2002 09:54:34 -0400

> for the routers that are connected to them within the ospf standard.

What do you mean by hide - is it a single network? The simple answer would
be to configure a tunnel between the two routers and run OSPF over the
tunnel rather than the physical network you are trying to hide.

--
Acee

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From: Markus Prison <[email-masked]>
Date: Fri, 26 Apr 2002 16:11:01 +0200

Hi Acee,

it will be a single broadcast network betweeen this two routers.
For ther routers around them it should look that there is no network between
them.

What do you meen with tunnel?

Markus

-----Ursprungliche Nachricht-----
Von: Mailing List [mailto:[email-masked]]Im Auftrag von Acee
Lindem
Gesendet: Freitag, 26. April 2002 15:55
An: [email-masked]
Betreff: Re: Hide a network between two routers

--
Acee

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From: Acee Lindem <[email-masked]>
Date: Fri, 26 Apr 2002 10:20:06 -0400

> What do you meen with tunnel?

I mean a GRE or IPIP tunnel.

You can do it with OSPF but it is ugly.

   1. Configure the "hidden" network in a separate area.
   2. Configure "no-advertise" ranges for the "hidden"
      network.
   3. Configure a virtual link between the two routers
      traversing the separate area.

--
Acee

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From: Anton Smirnov <[email-masked]>
Date: Mon, 29 Apr 2002 16:56:12 +0200

Markus,
   if I understood correctly, by 'hiding' the network you mean announcing it
in a way that all non connected routers know about the link and may use it
for transit traffic but are not aware of addressing associated with the
network.
   If above is correct then it is very easy to achieve. Just announce this
broadcast link in type-1 LSAs of both connected routers as type-1 link (you
wrote there are two routers on the link, right?). This change is seamless
for all non-connected routers. For connected routers it will require minor
changes in LSA origination code and, may be, in SPF code to calculate
correctly next hop information.

   Couple of years ago I played with this mechanism to achieve LSDB size
reduction for networks actively using broadcast media to interconnect two
routers (say, Ethernet crossover connections between routers). Goal was
different from what you are trying to achieve, because accent was on
autoconfiguration of the feature without involving much additional
signaling, and transit network addressing was still announced. But I
remember that actual code changes for this feature were very minimal. That
time I half-wrote a paper about this mechanism. If you are interested I can
find it, though I don't think it is of much help for your task.

Anton

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From: Acee Lindem <[email-masked]>
Date: Mon, 29 Apr 2002 11:18:55 -0400

Anton,

Along these same lines there is also:

http://www.ietf.org/internet-drafts/draft-ietf-isis-igp-p2p-over-lan-00.txt

Of course, to hide the network completely you have to treat the ethernet
as an unnumbered point-to-point interface.

Anton Smirnov wrote:
>>For ther routers around them it should look that there is no network
>>
> between
>
>>them.
>>
>>>my question will be if it's possible to hide a network between two
>>>
> routers
>

--
Acee

---

From: Anton Smirnov <[email-masked]>
Date: Mon, 29 Apr 2002 18:50:14 +0200

Acee,
   I didn't mention this paper to Markus just because it is also not exactly
what he needs.
   OSPF standard says that point-to-point interfaces do not need to use IP
address of neighbor in next-hop calculation, but this information is anyway
readily available and can be used if wanted to. So from OSPF perspective,
ptp operations on broadcast media happen almost automatically after
implementing initial standard - if proper method to configure such interface
as ptp has been provided, of course - and are working in several
implementations for many years. It is right thing to document it, though.

   Network operator has to configure broadcast links to be ptp if he wants
them to. So what I was interested in is, actually, method selfconfiguring
broadcast links as ptp if they are being used as ptp. It, obviously, makes
no sense without possibility to use broadcast links as ptp, but latter has
already been working in implementation I played with and I took it for
granted :-)

   I'm attaching the paper I mentioned, I hope it will explain technical
side better. I remembered it when I wrote email to Markus because he may
need to touch same areas of code and do something resemble. He needs to
think of all procedures himself, though, as his task seems to be rather
unusual. The paper is rather clumsy and heavy worded, but technical side is
simple.

Anton