default-information originate and Redistribute static ospf command

[mahesh18]

Hi,

I was redistributing static Routes to my OSPF  network Lab for learning purposes

R1 Router connects to Cable modem

ip route 0.0.0.0 0.0.0.0 70.x.x.x*****************************************Default route to ISP

ip route 172.31.0.0 255.255.255.0 Null0******************************************Static Routes

ip route 172.31.1.0 255.255.255.0 Null0

ip route 172.31.2.0 255.255.255.0 Null0

ip route 172.31.3.0 255.255.255.0 Null0

OSPF  Config

router ospf 1

router-id 4.4.4.4

log-adjacency-changes

redistribute static metric 50 metric-type 1 subnets***Command to redistribute Static Routes to OSPF Network

default-information originate

What i did was removed the default-information originate command from the R1 router ---   i was under the impression that redistribute static

command should advertise 70.X.x.x  network to my OSPF Lab.

After doing this R2 Router had no internet connection and default OSPF route .

My question is why removing the default -information originate command does not advertise ISP Network 70.x.x.x into my OSPF LAB?

Thanks

MAhesh

[Reza Sharifi]

Hi Mahesh,

You need both default-information originate command and also 0/0 (default route).  You need 0/0 in your route table in order for the default-information originate command to work, if not every thing goes to null0.

HTH

[mahesh18]

Hi Reza,

Thanks for reply.

So you mean to say that if i do not use default information originate command and i have only this command in R 1 config of R1

ip route 0/0  70.x.x.x    then all other routers in OSPF will have no default route ?

Other thing when you say that everything goes to null 0 it means say R2 has no default route now as we do not have default info command on R1.And we ping IP 4.2.2.2  from Router 2 and it comes to R1 as R1 now has no default originate command  then it matches that with

ip route 172.31.3.0 255.255.255.0 Null0  and packet goes to null?

should'nt R1 matches 4.2.2.2  with command ip route 0.0.0.0 0.0.0.0 70.x.x.x?

Thanks

MAhesh

[Reza Sharifi · Accepted solution]

Hi Mahesh,

By default, OSPF makes sure that your router advertises a default route (0/0)  only if it already knows about it. It does not matter where your did  your router get the default route from - it may be static or advertised  by some other routing protocol. it must first be  present in your routing table, only then it can be advertised in OSPF. Basically with default route, you are saying for everything come to me.

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801ec9f0.shtml

HTH

[JohnTylerPearce]

Well he has a default route configured as 'ip route 0.0.0.0 0.0.0.0 70.x.x.x'. Now correct me if I'm wrong, but I thought if you ran "default-information originate' command you had to have a default route in your routing table in order for it to advertise the route to all other routers in the same ospf area. Reza when you enter 'default-information originate' do you see a default route in R2 at all pointing to 70.x.x.x? Can you post the output of 'show ip route' from R2?

[mahesh18]

Hi Johntyler,

Router R2 will only show following

sh ip route on R2

O*E2 0.0.0.0/0 [110/1] via 192.168.5.3, 00:41:29, FastEthernet0/11

It will not show default Ip route to 70.x.x.x .

where 192.168.5.3 is IP of interface Fas  of R1 that connects directly to R2.

Thanks

MAhesh

[Julio Carvajal · Accepted solution]

Hello Mahesh 18,

You need to have the Default information originate in order to send the Default route (0.0.0.0) in the OSPF updates and insert it into the OSPF topology.

Here is some useful information.

redistribute static subnets command is used to redistribute static routes in OSPF, However static default route (ip route 0.0.0.0 0.0.0.0…) is  not injected in to OSPF topology database. IF you want to redistribute  the quad zero (0.0.0.0 0.0.0.0) static route in OSPF, following command should be used with in the  router ospf configuration.

     -default-information originate

Please rate helpful posts,

Kind regards,

Julio

[mahesh18]

Hi Julio,

Your explanation was very good .Now i understand that

default information originate and redistributed static are different commands and there use is different.

I was under the impression that redistributed static command will also cover the default information command work.

Thanks a Lot

MAhesh

[Peter Paluch · Accepted solution]

Hi Mahesh,

Just to add to other friends' awesome answers here, technically, there is no problem in redistributing the default route into OSPF. The OSPF protocol itself has no limitations on this - the default route is just another external route, anyway. However, it is an intentional safety check built into Cisco's OSPF implementation that makes sure that the default route will not be redistributed into OSPF when performing redistribution, and the only way to inject a default route into OSPF is using the default-information originate command. Consider it a safety and sanity check.

Other vendors' implementations may differ in this aspect.

Best regards,

Peter

[mahesh18]

Hi Peter,

Thanks for reply

Your explanation is always good--This forum is best place to learn as things which are explained by people like you is always great  and its hard to find elsewhere.

Regards

Mahesh

[Peter Paluch]

Hello Mahesh,

You are very much welcome! Thank you for the generous ratings!

Best regards,

Peter

[mahesh18]

Hi Reza,

Thanks once again.

Mahesh

[Julio Carvajal]

Hello Mahesh,

My pleasure , any other question I will be more than glad to help.

Kind regards,

Julio