OSPF network command

Answered Question
May 25th, 2007

what is the meaning of

"network 0.0.0.0 0.0.0.0 area n"?

what will be the function of above command?

Correct Answer by Richard Burts about 9 years 9 months ago

Dan

By default Cisco OSPF will advertise a loopback interface as a /32, no matter what subnet mask you configured on the interface. If you really want the entire subnet advertised then you change the network type of the loopback interface to point to point and then OSPF advertises the entire subnet.

Most of the interface network types are fairly obvious: Ethernet defaults to broadcast, PPP and HDLC default to point to point, frame relay point to point subinterfaces default to point to point. Frame Relay multipoint subinterfaces and Frame Relay on the physical interface default to multipoint. The significance of the network types in OSPF is that OSPF behaves somewhat differently on each type: point to point just forms adjacency and does not bother with DR or BDR. Broadcast must elect DR and BDR and then routers form adjacency with only the DR and BDR. multipoint has a different way of identifying neighbors.

If you have a serial link and the routers on that link have different network types they will probably not form an adjacency.

HTH

Rick

Correct Answer by Richard Burts about 9 years 9 months ago

Dan

the command network 0.0.0.0 0.0.0.0 area n does not make much sense. The wildcard mask of 0.0.0.0 specifies a match on all 32 bits which means that only the address 0.0.0.0 could match. But no interface will have address 0.0.0.0.

I wonder if you got this confused with:

network 0.0.0.0 255.255.255.255 area n

which will match all of the interfaces on the router, will put all of these interfaces into the OSPF process and assign them to area n.

It is an easy kind of shortcut way to configure the OSPF to avoid having to type multiple OSPF network statements.

HTH

Rick

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (4 ratings)
Loading.
Correct Answer
Richard Burts Fri, 05/25/2007 - 10:55

Dan

the command network 0.0.0.0 0.0.0.0 area n does not make much sense. The wildcard mask of 0.0.0.0 specifies a match on all 32 bits which means that only the address 0.0.0.0 could match. But no interface will have address 0.0.0.0.

I wonder if you got this confused with:

network 0.0.0.0 255.255.255.255 area n

which will match all of the interfaces on the router, will put all of these interfaces into the OSPF process and assign them to area n.

It is an easy kind of shortcut way to configure the OSPF to avoid having to type multiple OSPF network statements.

HTH

Rick

dangal.43 Fri, 05/25/2007 - 11:09

rick,

thanks for your reply. One more question when do we need to change the Network types to point to point of the LOOPBACK interface in OSPF?

what is the default Network types of the various interface in OSPF configuration?

and what is the significant of it....

what if i will have two router connected witht the serial interface and they have different network types on both the ends.... do they will become a neighbor?

Correct Answer
Richard Burts Fri, 05/25/2007 - 11:18

Dan

By default Cisco OSPF will advertise a loopback interface as a /32, no matter what subnet mask you configured on the interface. If you really want the entire subnet advertised then you change the network type of the loopback interface to point to point and then OSPF advertises the entire subnet.

Most of the interface network types are fairly obvious: Ethernet defaults to broadcast, PPP and HDLC default to point to point, frame relay point to point subinterfaces default to point to point. Frame Relay multipoint subinterfaces and Frame Relay on the physical interface default to multipoint. The significance of the network types in OSPF is that OSPF behaves somewhat differently on each type: point to point just forms adjacency and does not bother with DR or BDR. Broadcast must elect DR and BDR and then routers form adjacency with only the DR and BDR. multipoint has a different way of identifying neighbors.

If you have a serial link and the routers on that link have different network types they will probably not form an adjacency.

HTH

Rick

dangal.43 Fri, 05/25/2007 - 11:31

will you please give me some highlites on FR networks various combination?

actually i read that but its look like little bit difficult for me to understand it as i got confuse in it.... so when to use the neighbor command and when i cannot use it?

dangal.43 Fri, 05/25/2007 - 11:34

what if i will have router connected with the layer2 switches in same vlan and if i will change the network type of one of the router interface among the all others then what will happen? let say i will have 4 router and one switch..... all 4 routers are connected with the one switch and if i will change the network type of one of the router interface..... then will all other router will have neighborship with that router.....

Richard Burts Fri, 05/25/2007 - 12:38

Dan

Without specifying what the relationships are and without specifying what network type you would change to it is hard to say exactly what the effect would be. But I believe that in general if you have 4 routers connected through a switch then they would default to being broadcast. If you then change the network type of 1 router to be something else, then I believe that the 1 router would most probably not form adjacency with the other 3.

HTH

Rick

dangal.43 Fri, 05/25/2007 - 11:17

Rick one more question about the OSPF fast hello.... will it be good to enable it in MPLS Service Provider environment router?

all routers are using the Gigabyte Ethernet interfaces....

Richard Burts Fri, 05/25/2007 - 12:35

Dan

I do not have direct experience with the OSPF fast hello feature. Based on what I know about it I believe that it is more suited for use in LAN environments. I wonder what the effect would be on MPLS if OSPF were sending multiple HELLO messages per second.

HTH

Rick

dangal.43 Fri, 05/25/2007 - 12:51

so i think MPLS and OSPF both are the different process in one Network domain. So i think enabling the OSPF fast hello will not affect the MPLS but it will have some over head and some more processing as hellos are sending at the very higher rate on the other hand i will have the fast convergence, right!!!

Richard Burts Fri, 05/25/2007 - 13:05

Dan

You certainly would get faster convergence and you certainly would have higher over head.

HTH

Rick

dangal.43 Fri, 05/25/2007 - 13:19

thanks Rick for your information and time..... that helps me lot for understanding the various points..... its really good to have experts like you in this forum to resolve the issues of various networking technology....

Richard Burts Fri, 05/25/2007 - 13:29

Dan

I am glad that my answers were able to help you to resolve your questions. Thank you for using the rating system to indicate that your questions were resolved (and thank you for the ratings). It makes the forum more useful when people can read a question and can know that they will read an answer that resolved the question.

The forum is a very useful place for getting questions answered and in understanding how things work. I encourage you to continue your participation in the forum.

HTH

Rick

Actions

This Discussion