OSPF area range command

[raghav.rai]

Hello,

I have below config in one of the switches in the network. I have an SVI in the device (interface vlan100) which has a /24 subnet. OSPF has network statement for bigger pool that is /16. Since config has area range command it is generating a * directly connected, via Null0 route in it. This null0 route is not allowing me to use another /24 from the same /16 range in another switch during a refresh activity. How can I make ospf not to create this directly connected, via Null0 route for the /16 subnet? any suggestions? My assumption is if I remove area 10 range 10.1.0.0 255.255.0.0 will fix the issue. 

#Core-Switch

interface vlan100
ip vrf ABC
ip address 10.1.10.1 255.255.255.0
no shut

router ospf 10 vrf ABC

router-id 10.100.1.8

log-adjacency-changes

auto-cost reference-bandwidth 100000

area 10 stub no-summary

area 10 range 10.1.0.0 255.255.0.0

redistribute bgp 65100 metric 1 subnets

passive-interface default

no passive-interface Vlan97

no passive-interface Vlan98

network 10.100.1.8 0.0.0.0 area 10

network 10.1.0.0 0.0.255.255 area 10

Core-Switch#sh ip route vrf ABC 10.1.12.1

Routing entry for 10.1.0.0/16

Known via "ospf 10", distance 110, metric 0, type intra area

Redistributing via bgp 65100

Advertised by bgp 65100 metric 1 match internal external 1 & 2

Routing Descriptor Blocks:

* directly connected, via Null0

Route metric is 0, traffic share count is 1

[MHM Cisco World · Accepted solution]

NO discard-route external/internal

Try above command 

But But But 

This to null0 route is add to prevent routing loop.

Be careful 

Thanks 

MHM

[raghav.rai]

Thank you MHM.

Are you saying remove area 10 range 10.1.0.0 255.255.0.0 command will not work here?

My understanding was null0 route is added by above range command.

Just wondering how null0 route is preventing routing loops. 

[MHM Cisco World]

For example I have 

R1-R2

In R1 10.1.1.0/24 

And I summary it to 10.1.0.0/16' this new prefix includes 10.1.1.0 10.1.2.0 10.1.3.0...etc' 

This make R2 send traffic for other prefix includes in summary to R1' R1 dont have direct or learn this prefix.

So it will use defualt route' and if it toward R2 then the traffic enter in loop 

R2 send to R1 and R1 resend to R2

Here null0 come 

10.1.0.0/16 null0 

R1 when receive any prefix includes in summary and not direct connect or learn' it will drop it (to null0).

And hence that why router ios auto add this to null0 route.

MHM