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Re: OSPF multi-level hierarchy: Necessary at all?

  • From: Alex Zinin
  • Date: Thu May 27 13:41:45 1999

>> Well, you do know that you can create loopback interfaces and the router-ID
>> will be the highest one among them. Say you do:
>> int lo 0
>>  ip address
>Hmm. Try yourself. Then, the quote from my config:
>interface Loopback98     
> description Router-ID     
> ip address
>I even proposed to declare 223.255/16 as private block -:).

Ah, yeah, forgot about the range :) but you got the idea.

>> >network and name his _AREA with the strict filtering on the 
>> >border.
>> I was thinking about it as well. One could configure some area range
>> as a "discard" one, effectively saying that all routes dropping into the
>> range should be ignored instead of announced in a summary-LSA.
>I am not sure if it's the same what I was saying, but approx. it is. We 
>need good inter-area routing with the distribute-control over it. We can 
>control exported prefixes by -STUB AREA- definition and/or 
>summarisations, but we can't control incoming routes,

Mmmm...I believe you mean we can control imported (import/export...:)) 
hey, let's say external) routes with stub areas.

>Btw, do you know _GATED_? It allow to control IMPORTED routes, but for 
>OSPF_ASE_ routes only. 

Actually in Cisco you can apply distribute-list to the whole process and it
will be able to control which routes are installed into the routing table
or got redistributed from it. You cannot control what is exchanged between
routers, of course.

>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.

>but why don't do 
>it on the area boundaries?

We should be able to but not now, unfortunately.
I actualy have heard some rumors Cisco's gonna support
this type of filtering.

>> >This is reason why ISP don't like OSPF and such protocols - they can be 
>> >used for the inter-router routing, but they can't be used to connect with 
>> >the customers (no, I can run 10 different OSPF processes and re-advertise 
>> >routes - one more headache for the network admins).
>> Actually, you can use NSSA, but doesn't allow for filtering either.
>Sorry, what's NSSA?

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.

>> >PS. From ISP's point of view. What I'd like.
>> >
>> [snip: got your wish, Alex]
>> >3) Moreover, why can't I determine different BGP AS numbers for the boths 
>> >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?

Alex D. Zinin, Consultant
CCSI #98966
CCIE #4015
AMT Group / ISL 
Cisco Systems Gold Certified Partner
irc: //EFNET/#cisco, // [Ustas]