From: David Luu (wicked01@xxxxxxxxxxxxx)
Date: Fri Jun 28 2002 - 21:47:53 GMT-3
this will also block R3' from getting the route, so you need to add a
static or default route for R3 which will not get propagated into ospf's area 0
>Date: Fri, 28 Jun 2002 17:41:56 -0700
>To: ccielab@groupstudy.com
>From: David Luu <wicked01@ix.netcom.com>
>Subject: Re: OSPF route filtering teaser
>
>there is also another way,...and will literally "block" the ospf
>10.1.0.0/16 route...
>
>this only needs to be done on R3
>
>distribute-list 1 in
>access-list 1 deny 10.1.0.0 0.0.255.255
>access-list 1 permit any
>
>>Date: Fri, 28 Jun 2002 17:28:09 -0700
>>To: Carlos G Mendioroz <tron@huapi.ba.ar>, ccielab@groupstudy.com
>>From: David Luu <wicked01@ix.netcom.com>
>>Subject: Re: OSPF route filtering teaser
>>
>>forgot to add...
>>
>>2 ospf processes on R3
>>
>>At 07:35 PM 6/28/2002 -0300, Carlos G Mendioroz wrote:
>>>David,
>>>how do you "block" routes in an OSPF link ?
>>>
>>>David Luu wrote:
>>> >
>>> > sounds simple enough...
>>> >
>>> > use route tags
>>> >
>>> > have R2 set a tag for the 10.1.0.0/16 and have R3 block the tag going
>>> into
>>> > area 0
>>> >
>>> > At 09:10 PM 6/28/2002 +0100, Peter Whittle wrote:
>>> > >Selectively blocking OSPF routes between areas
>>> > >----------------------------------------------
>>> > >
>>> > >I would like to pose a simple scenario to the group.
>>> > >
>>> > >There are 4 routers R1 .. R4
>>> > >
>>> > >R1 is injecting routes into RIPv2 say 10.1.0.0/16
>>> > >
>>> > >R2 is running RIPv2 on e0, it is also connected by e1 to OSPF Area 1 and
>>> > >must inject the routes learnt from RIP into AREA 1. There are other
>>> > >routers also connected to the ethernet segment in Area 1 again running
>>> > >OSPF. The routes injected by R2 into area 1 must be visible to these
>>> > >routers via OSPF.
>>> > >
>>> > >R3 has 2 ethernet interfaces e0 in OSPF Area 0, and e1 in OSPF Area 1.
>>> > >It must see the RIP routes injected into OSPF by R2 (ie 10.1.0.0/16).
>>> > >
>>> > >R4 in connected to the ethernet in Area 0 and is also running OSPF and
>>> > >is outside of your control.
>>> > >
>>> > >STOP the RIP routes that were injected by R2 from being seen in Area 0.
>>> > >(i.e. block the 10.1.0.0/16 route)
>>> > >
>>> > >You may only program routers R2, & R3 to achieve this.
>>> > >
>>> > >
>>> > >Any thoughts, ideas, solutions?
>>> > >
>>> > >
>>> > >I have one solution in mind but it is not very elegant. I will share
>>> > >this next week when you have had time to think about the problem.
>>> > >
>>> > >
>>> > >------------
>>> > >
>>> > >A distribute-list applied to R3, an ABR, will of course not work. (When
>>> > >the 10.1 route reaches R3 it is in an LSA. If we apply the distribute-
>>> > >list x in, it will only block the route going into R3's routing table,
>>> > >it will not prevent the LSA from being sent on to R4. We are not
>>> > >permitted to change the other routers in Area 0 so we can not use the
>>> > >conventional approach of applying the distribute-list x in to each of
>>> > >the routers in Area 0.
>>> > >
>>> > >If we apply a distribute-list x out to the ABR it will again have no
>>> > >impact on the LSA advertising the 10.1 route into Area 0.)
>>> > >
>>> > >==========================
>>> > >
>>> > >May enlightenment be yours.
>>> > >
>>> > >Peter
>>> > >
>>> > >--
>>> > >Peter Whittle
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