OSPF multi-level hierarchy: Necessary at all?

Alex P. Rudnev alex at Relcom.EU.net
Thu May 27 17:59:14 UTC 1999

Now I can say what I'd like to have.

I'd like to have any way of inter-connection two DIFFERENT OSPF networks 
by such way that other network look like AREA (or STUB AREA) for the 
local network.

This is:

(the view of network admin A):

-- Network-a - ABR1 -Area_1
(ABR - Area Border Router)

For the admin-2 everything looks like:

Area_2 --  ABR-2 - network-b

Network admin 1 control Network-a with ABR-1, and define link to ABR-2 as 
usial link to the Area_1. Network admin 2 control network-b and define 
link to ABR-1 as the link to Area_2. Both Network-a and Network-b have 
their own backbones and the set of routers.

moreover, to realise it, you need not new OSPF protocol, it can be 
implemented in ABR-1 and ABR-2. For now  it can be modelled by running 
'router ospf 1' and 'router ospf 2' on the same router, with the 
readvertising from one router to another, but it's configured by some 
tricky way and does not present network-b or network-a as an AREA 
(causeing some limitation and extra manual configurations).

> >I don't think it's possible to control route 
> >import anywhere except area borders (for the OSPF case), 
> sure it is not, because you need to have syncronized LSDBs for all
> routers to calculate identical shortest paths.

> >> Actually, you can use NSSA, but doesn't allow for filtering either.
> >Sorry, what's NSSA?
Oh, sorry, I know what;s it but did not read this abbreviation before.

> Not-So-Stubby Area, it works like a stub one, but allows to have an ASBR
> in it. So it does not accept ASE-LSAs from the domain, but can be used
> to inject externals into it.
It's just the model of ISP-customer, btw.

> >> >ISP and CUST OSPF zones. 
> >> 
> >> who said you can't ? or I'm missing something?
> >Yes, I can. But no one (except me) know about it -:).
> >
> >I mean some mixturing of OSPF and BGP properties. They are mixtured 
> >already - OSPF tag can hold 1 BGP paths. Through I don't think it's 
> >important for now.
> you mean RFC 1403?
Am not sure about # RFC, but yes - I mean this old schema when OSPF keep 
short BGP information - this was the way first OSPF/BGP networks was 
built by.

> Alex.
> ------------------------------------------------------------------
> Alex D. Zinin, Consultant
> CCSI #98966
> CCIE #4015
> AMT Group / ISL 
> Cisco Systems Gold Certified Partner
> http://www.amt.ru
> irc: //EFNET/#cisco, //irc.msn.com/#NetCisco [Ustas]

Aleksei Roudnev, Network Operations Center, Relcom, Moscow
(+7 095) 194-19-95 (Network Operations Center Hot Line),(+7 095) 230-41-41, N 13729 (pager)
(+7 095) 196-72-12 (Support), (+7 095) 194-33-28 (Fax)

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