Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member


In OSPF v2, when we say net ar 0. what this command does? for example on a router, say B, when we advertise this command. what this does?


Re: OSPFv2


network area

the ip-address/wildcard combination work similar to the pattern matching in ACLs; all the matching IP-interfaces of the router will be advertised by OSPF. Neighbor-discovery will start on broadcast-capable interfaces by sending OSPF hello as well (as long as you don't configure them as passive interfaces).

In your example, router B will advertise the network of the IP interface which has the exact IP address in Area 0 (if such an IP interface exist).



Super Bronze

Re: OSPFv2


The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.


Hi, I just want to re-emphasis what Rolf already described.  The OSPF network statement doesn't directly advertise a network, it "looks" for "up" interfaces that have an IP that matches against the network statement (als also mentioned by Rolf, somewhat like an ACL).  Once if finds such an interface, that interface will be included in the OSPF.  As Rolf also notes (by default) active OSPF interface are what are used to form adjacencies with neighboring OSPF routers.

Also, when it comes to what network's mask is, that is determined by the interface's IP mask.

The area parameter determine which OSPF area the interface will be part of.

Something else to note, the network statements can overlap in matching, allowing most of an address block to be assigned to one OSPF area, while allowing more specific subnets, within the address block, to be assigned to another OSPF area.

Usually, you'll see network statements that match specific IPs or you'll see a single network statement that matches all (or many) interfaces IPs.


int x

ip address

int y

ip address

router ospf #

network area #

network area #


router ospf #

network area #

CreatePlease to create content