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New Member

ospf

Hi..

I need some clarification in ospf. if i run two ospf process id(router ospf 5 & router ospf 10) and advertise different-different nettwork in both ospf process then would there be possibility of exchanging routes from process 5 into 10 or vice versa.

 

Also can a network(like 10.10.100.0/24) be advertised on two ospf process. Pls make me clear.

  • WAN Routing and Switching
7 REPLIES
New Member

Hi Anukalp, No. If you have

Hi Anukalp,

 

No. If you have two separate OSPF processes, they do exchange routes between the processes even if the processes are on the same device. To do so, you'd need to redistributed one process into another.

 

To your second question, yes. You can advertise the same net from two ospf processes.

See the "Why does this problem occur?" Section in the below doc:

http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/28025-2ospf-redis.html

 

Rate if helpful

New Member

For example if you follow the

For example if you follow the below example :

router ospf 1
 router-id IDCCISCOFWUS01
 network 172.16.0.0 255.255.255.128 area 0
 network 172.24.0.128 255.255.255.224 area 0
 network 172.24.255.128 255.255.255.224 area 0
 network 172.24.255.160 255.255.255.224 area 0
 area 0 authentication message-digest
 log-adj-changes
 redistribute static subnets
 redistribute ospf 65535 subnets route-map Ospf-Filtro-Mpls-From-Infracom-To-Idc
!
router ospf 65535
 router-id 192.168.252.20
 network 192.168.253.216 255.255.255.248 area 6
 area 6 authentication message-digest
 log-adj-changes detail
 redistribute static subnets tag 100 route-map Static-Filtro-Mpls-From-Idc-To-Infracom
 redistribute ospf 1 subnets tag 100 route-map Ospf-Filtro-Mpls-From-Idc-To-Infracom


 

Cisco Employee

Hello Anukalp , Yes , you may

Hello Anukalp ,

 

Yes , you may achieve it by redistributing one ospf process into another and vice versa . 

 

I hope this answers your question .

 

Regards

Sunil Bhadauria

Hall of Fame Super Silver

I agree with the previous

I agree with the previous responses that the answer to your first question is fairly straightforward. If you have two OSPF processes on the same device they will not advertise each others routes by default. To have one OSPF process advertise routes from the other process would require some explicit configuration such as redistributing routes.

 

I believe that we need to be careful in the answer to your second question. How does the route for 10.10.100.0/24 exist? Is it a single subnet on a single interface? Is it multiple smaller subnets being summarized? If it its a single subnet on a single interface then it is easy to advertise it in one OSPF process. But to advertise that subnet in the second OSPF process would require something like redistribution. If it is several smaller subnets then perhaps some subnet(s) are in one OSPF process while other subnet(s) are in the other OSPF process. Then each OSPF process could summarize and advertise the /24.

 

HTH

 

Rick

New Member

Thanks Rick for clarifying my

Thanks Rick for clarifying my first query.

For second query, i have a vlan interface having ip 10.10.100.0/24 on L3 switch. On this device i want to run two ospf process.  can i advertise this network on under both process. I dont want to redistribution but want this network to reach from two locations, one running a ospf process and another location running another process.

is this possible?

Hall of Fame Super Silver

Let me start the response by

Let me start the response by reviewing some basic behaviors of OSPF. We normally get OSPF to advertise a subnet by configuring a network statement in the OSPF process that matches the interface. You certainly can configure a network statement matching the vlan interface for both OSPF processes. But here is where it gets tricky. Only one OSPF process will run on the interface. If the second OSPF process starts to run on the interface and finds that there is already an OSPF process running on the interface then the second process will not run on the interface unless the first process stops running on the interface.

 

So you can not advertise the 10.10.100.0 in both processes using network statements in each process. What is left to accomplish the advertisement is some type of redistribution. I am not sure why you do not want to redistribute, but I do not see a way to advertise in both processes without redistribution into one of the processes.

 

HTH

 

Rick

Cisco Employee

And just add what Richard

And just add what Richard explained above ,

 

You may add same prefix to different process but advertisement will only be made to the neighborship which comes up first . 

 

Regards

Sunil Bhadauria

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