From: Kian Wah Lai (kian_wah@qala.com.sg)
Date: Fri Apr 22 2005 - 22:39:37 GMT-3
Hi,
Actually there is a public PDF file on NMC tech lib that describes this
issue.
I have uploaded it to
https://s8.yousendit.com/d.aspx?id=3L8ECMX15AMXV1GNZI31ON37TS
for those who are interested.
Regards,
Kian Wah
http://www.aces-star.com
Your Asia rack rental source.
Ace the CCIE lab with it
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccie2be
Sent: Saturday, April 23, 2005 6:34 AM
To: 'Dennis J. Hartmann'; Group Study
Subject: RE: OSPF Wildcard Mask -> NMC Scenario# 2
Dennis,
You raise an interesting and important point.
Here's the deal.
Originally, I always did the same thing you did - use a mask of 0.0.0.0
But, there are times when this isn't what you want.
I'd have to check but I learned from one of the practice labs I did why you
shouldn't always use the 0.0.0.0 mask.
Here's the scenario:
R1
|
|------------------------------|
| |
R2 R3
R2 is running IGP-x (it doesn't matter which IGP).
R1 is running IGP-x and ospf and is redist betw IGP-x and ospf.
R3 is running only ospf.
Now, assume you have traffic that should go from R3 to R2 or beyond.
Probably you don't want the packet to make a pit stop at R1 since if it did,
the packet would go in and leave the same interface wasting time and
resources.
Depending upon how you configure the mask will determine if that packet
makes a pit stop or not.
If you use a mask of 0.0.0.0, you'll have a pit stop.
If you use any other mask, no pit stop.
HTH, Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Dennis J. Hartmann
Sent: Friday, April 22, 2005 6:12 PM
To: ccielab@groupstudy.com
Subject: OSPF Wildcard Mask -> NMC Scenario# 2
I've been noticing in most scenarios that the OSPF routing protocol is
being advertised with the wildcard mask for the interface in which it's
being advertised.
Example
Interface Fast 0/0
ip address 172.16.20.2 255.255.255.128 (/25)
router ospf 1
network 172.16.20.0 0.0.0.127 area 3
I would never do it this way, I would specify the exact IP Address of
the interface and a wildcard mask of 0.0.0.0 as shown below:
router ospf 1
network 172.16.20.2 0.0.0.0 area 3
The scenario does not call for any "special type of advertising in any
way. Is there a valid reason why I would ever use the wildcard mask that
the NMC answer is giving?
Sincerely,
Dennis J. Hartmann
White Pine Communications
CCSI#23402/CCIP/CCNP/CCDP/CCNA/CCDA
Cisco IP Voice Support & Design Specialist
Cisco Optical, VPN & IDS Specialist
MCSE
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