This is only applicable for the CCIE exam as loopbacks are used to generate
networks

 

If you have a Loopback as follows

 

interface Loopback0

 ip address 192.168.1.1 255.255.255.0

 

And you add the above to OSPF it will show up as

 

192.168.1.1/32

 

If you have a question that asks you to see that as a network not a host you
would need to

 

interface Loopback0

 ip ospf network point-to-point

 

It will then show up in the routing table as

 

192.168.1.0/24

 

Regards,

 

Tyson Scott - CCIE #13513 R&S, Security, and SP

Managing Partner / Sr. Instructor - IPexpert, Inc.

Mailto:  <mailto:[email protected]> [email protected]

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From: [email protected]
[mailto:[email protected]] On Behalf Of Kingsley
Charles
Sent: Monday, August 23, 2010 6:23 AM
To: Yogesh Gawankar
Cc: [email protected]
Subject: Re: [OSL | CCIE_Security] ip ospf network point-to-point under
loopback interface with ospf

 

Hi Yogesh

I am asking this for cases like DMVPN, GETVPN where we advertise loopback
interfaces. But if we clear CCIE security, then definitely R & S would be
easier as without knowing R&S, we can't clear CCIE Security :-)

After Security, next is R&S for me....


With regards
Kings

On Mon, Aug 23, 2010 at 3:26 PM, Yogesh Gawankar <[email protected]>
wrote:


Hi kings

 

yes you are right.By the way have you started studying for R/s track too? :)

 

This sounds more like an R/S question.

Thanks and regards

Yogesh Gawankar



--- On Mon, 8/23/10, Kingsley Charles <[email protected]> wrote:


From: Kingsley Charles <[email protected]>

Subject: [OSL | CCIE_Security] ip ospf network point-to-point under loopback
interface with ospf
To: [email protected]

Date: Monday, August 23, 2010, 7:22 PM

 

Hi all

Sinppet from
http://www.cisco.com/en/US/tech/tk365/technologies_q_and_a_item09186a0080094
704.shtml#qone


Why are loopbacks advertised as /32 host routes in OSPF?


A. Loopbacks are considered host routes in OSPF, and they are advertised as
/32. For more information, refer to section 9.1 of RFC 2328
<http://www.ietf.org/rfc/rfc2328.txt>   leavingcisco.com
<http://www.cisco.com/images/exit.gif> . In Cisco IOS Software Releases
11.3T and 12.0, if the ip ospf network point-to-point command is configured
under loopbacks, OSPF advertises the loopback subnet as the actual subnet
configured on loopbacks. ISDN dialer interface advertises /32 subnet instead
of its configured subnet mask. This is an expected behavior if ip ospf
network point-to-multipoint is configured.




This statement is applicable only when the loopback address is not
configured with subnet mask of 255.255.255.255, right?



With regards
Kings

 

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