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Re: OSPF reverse mask posted 04/21/2000
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I agree with the majority, easier to use a 0.0.0.0 mask specifying each
interface that is participating in OSPF, unless all router interfaces are
participating, then one statement of :
network 0.0.0.0 255.255.255.255 area x
is more sensible

However, you should be just as comfortable calculating inverse masks as you
are standard ones, basically there are only 8 variations of each:

Standard    Inverse
255            0
254            1
252            3
248            7
240            15
224            31
192            63
128            127
0                255

so 255.255.224.0 standard is 0.0.31.255 inverse
or 255.255.255.240 standard is 0.0.0.15 inverse

etc.

In my experience, you are more likely to blow an inverse mask in an
access-list than in an OSPF network statement, cause you'll do way more of
them...


Chad Marsh
CCIE# 5185

----- Original Message -----
From: Stanley Seow <stanley_seow@xxxxxxxxxxxxxxxxxxx>
To: CCIELAB <ccielab@xxxxxxxxxxxxxx>
Sent: Thursday, April 20, 2000 6:42 AM
Subject: OSPF reverse mask


> A quick question....
>
> For example, if the OSPF area X have a /22 bit mask...for the
configuration
> on the router, can I use the specific interface IP address (host mask )
>
> network 172.16.1.1 0.0.0.0 area 0
> network 172.16.5.1 0.0.0.0 area 1
>
> instead of calculating the reverse mask for odd subnet bit like /22 /25
/26
> /27.
>
> What is the differences betwen the above two reverse mask ??
>
> Stanley
>
>
>
>
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