From: Peter van Oene (pvo@xxxxxxxxxxxx)
Date: Wed Apr 24 2002 - 19:46:29 GMT-3
That command forces the ABR to summarize all routes in the range that exist
in Area 0 and package only the summary route in the type 3 that it sends to
other areas. Hence, you can summarize into, or out of the backbone. In
this case, it's an out of.
Pete
At 03:54 PM 4/24/2002 -0500, Ambern, Jeff wrote:
>Doesn't "area 0 range 172.10.7.0 255.255.255.0" create a type-3 summary
>from area 0? Therefore, shouldn't R4 be able to use the summary? I still
>think that R4 is seeing an O and an IA route and choosing the O for the
>routing table entry. I guess I will have to skim through the RFC for
>awhile.
>
>Jeff
>
>
>-----Original Message-----
>From: Peter van Oene [mailto:pvo@usermail.com]
>Sent: Wednesday, April 24, 2002 3:34 PM
>To: Ambern, Jeff
>Cc: 'ccielab@groupstudy.com'
>Subject: RE: How does OSPF enter routes into the routing table?
>
>
>Actually, I didn't read the whole thread. In this case, the /24 should
>disappear when the virtual link comes up.
>
>In the example, with R2 ---R5 ---- R4 as the topology, before the virtual
>link from R4 comes up, R4 is an internal router from an OSPF
>perspective. As such, it is able to use the type 3 from R5 which describes
>the /24 network. However, as soon as the virtual link comes up, R4 becomes
>an ABR. ABR's are only allowed to use type 3's from area 0, and thus the
>type 3 it was using from R5 becomes unusable. Hence, the /24
>disappears. R4 then learns the /28 via the type 1 that it picks up in area
>0.
>
>The order of preference between OSPF routes is irrelevant in this case as
>is the relative depth of the subnet mask. The fact that ABR's cannot use
>type 3's from non backbone areas is the primary lesson here. This behavior
>is specified in the RFC, and is there to prevent looping.
>
>Pete
>
>
>At 03:24 PM 4/24/2002 -0500, Ambern, Jeff wrote:
> >Please explain your reasoning. I'm don't see
> >why the behavior should be different.
> >
> >Jeff
> >
> >-----Original Message-----
> >From: Peter van Oene [mailto:pvo@usermail.com]
> >Sent: Wednesday, April 24, 2002 1:36 PM
> >To: Sam.MicroGate@usa.telekom.de; jambern@MerchantWired.com
> >Cc: ccielab@groupstudy.com
> >Subject: RE: How does OSPF enter routes into the routing table?
> >
> >
> >In this case, both should go into the table.
> >
> >At 12:19 PM 4/24/2002 -0400, Sam.MicroGate@usa.telekom.de wrote:
> > >I think you are correct. The same prefixes with two different subnet
>masks.
> > >R4 receives 172.10.7.0/24 O IA and 172.10.7.0/28 O and then installs the
> >/28
> > >in the routing table. That is because, of cource, it is O.
> > >
> > >Sam
> > >
> > >-----Original Message-----
> > >From: Ambern, Jeff [mailto:jambern@MerchantWired.com]
> > >Sent: Wednesday, April 24, 2002 11:25 AM
> > >To: 'Sam.MicroGate@usa.telekom.de'
> > >Cc: 'ccielab@groupstudy.com'
> > >Subject: RE: How does OSPF enter routes into the routing table?
> > >
> > >
> > >I still believe that it has to do with the prefix being the same length
> > >and the first route is an intra-area route. Try making the /28 something
> > >other than subnet-zero and see the /24 shows up in the routing table.
> > >
> > >Jeff
> > >
> > >-----Original Message-----
> > >From: Sam.MicroGate@usa.telekom.de [mailto:Sam.MicroGate@usa.telekom.de]
> > >Sent: Wednesday, April 24, 2002 10:18 AM
> > >To: jambern@MerchantWired.com
> > >Subject: RE: How does OSPF enter routes into the routing table?
> > >
> > >
> > >What about the scenario below? did you take a look at it?
> > >
> > >Sam
> > >
> > >-----Original Message-----
> > >From: Ambern, Jeff [mailto:jambern@MerchantWired.com]
> > >Sent: Wednesday, April 24, 2002 11:14 AM
> > >To: 'Sam.MicroGate@usa.telekom.de'
> > >Subject: How does OSPF enter routes into the routing table?
> > >
> > >
> > >Ospf will insert Intra-Area routes into the routing table befor
>Inter-Area
> > >routes.
> > >The order of preference is:
> > >O
> > >IA
> > >E1
> > >E2
> > >Jeff
> > >
> > >
> >
> >--------------------------------------------------------------------------
> > >Hello all,
> > >
> > >Last night I worked in a distribution lab from fatkid.com. In this lab I
> >had
> > >the following problem:
> > >Area 2 is configured a virtual area between routers R5 and R4. I used
>area
> >0
> > >range command to summarize the /28 subnet into area 2. Now the problem is
> >R4
> > >receive both routes the 172.10.7.0/28 as O and 172.10.7.0/24 as O IA and
> > >strangely choose the first to install in the routing table. The /24
>subnet
> > >gets suppressed and does not make it to the routing table. Shouldn't I
>see
> > >both routes in R4 because OSPF supports VLSM? Why OSPF choose the route
> >with
> > >the longer mask and ignored the one with shorter mask? If this the
>default
> > >behavior, How can I make the summary address /24 reach R4. Thank you all
> >for
> > >your help.
> > >
> > >
> > >
> > >172.10.7.0/28 172.10.128.0/26 LB0:172.10.5.4/24
> >
> >R2------------------------------R5------------------------------R4---------
> >-
> > >-------------------
> > >area 0 area 2 area 3
> > >Frame Relay Ethernet LB of R4
> > >
> > >At R5:
> > >area 0 range 172.10.7.0 255.255.255.0
> > >
> > >
> > >
> > >
> > >Elsayed Mohamed
> > >Sr. Network Consultant
> > >Microgateds, Inc.
> > >732-936-4413
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