From: Mohammad Saeed (mzsaeed@gmail.com)
Date: Thu May 24 2007 - 14:58:20 ART
Technically there shall be no problem, as 10.10.0.0 255.255.224.0 OR
10.10.4.0.0 255.255.224.0 will result in the same summary, if router
is "intelligent enough" to see that first 19 bits are network address,
so I don't care what you put in the later 13 bits as it has 0 in the
subnet mask. But may be as we are trying to "summarize networks"
router doesn't like some bit set to 1 in the host portion as normally
we represent network address with all ZERO in the host portion. May be
some one from our "Dear Instructors" can shed more
light on it.......
Regards,
Mohammad Zahed Saeed
On 5/24/07, Nisar, Munsar <munsar.nisar@citi.com> wrote:
> Look at the three common bits in the third octet and you would get the
> answer to your own question: all the common bits are zero so your third
> octet should be zero as well. Thanks.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Shamin
> Sent: Thursday, May 24, 2007 8:04 AM
> To: Cisco certification; Cisco certification
> Subject: OSPF AREA RANGE , Problem
>
> Dear All,
>
> I have a rather basic question. If someone can clear it off.
>
> I have the topology as below.
>
>
> Area 1 Area 0
> R2 <----------------------> R3 <---------------------> R4
>
> I am running Ospf Area 1 between R2 & R3 , and Area 0 between R3 & R4.
>
> R4 has 4 loopback interfaces with the following IP's advertised into
> Area 0
>
> 10.10.4.1
> 10.10.18.1
> 10.10.20.1
> 10.10.25.1
>
> The requirement is that, R2 sees a single route all these 4 networks.
> So we have to configure a area range command.
> Now my qestion is , If the question is that the summary should be as
> specific as possible,
> how will the summary configuration be like.
>
> The binary for the 3rd octet is as below,
> 4 - 00000100
> 18 - 00010010
> 20 - 00010100
> 25 - 00011001
>
> As per my understanding, we can configure to the summary to be till the
> 19th
> bit. i.e 255.255.224.0
>
> So should the configuration be on R3 as below:
>
> router ospf 1
> area 0 range 10.10.4.0 255.255.224.0
>
> OR
>
> router ospf 1
> area 0 range 10.10.0.0 255.255.224.0
>
>
> With the 1st config, the router gives a error, that of an Iconsistent
> mask.2nd config is accepted
>
> Can any one guide me as to which is the correct config and is my
> configuration meeting the requirement
> that the summary shoyld be as specific as possible.
>
> Regards
> All the best in your preprations
>
> Shamin
>
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