Communication of Different OSPF Domains in Juniper

Different OSPF Domains

Many engineers have good knowledge about OSPF to implement their network. Today, I will explain  a little more advanced details about OSPF. What do  you think  how to we make whether we communicate two  or more  different OSPF domains? Below, you will see how it is done in Juniper. As you guess this process will be helpful  if you are in  migration of two companies to each other or in large ISP networks. Please see below my topology which includes two different OSPF domains.

In fact, providing this communication is very simple as long as you consider some critical points. To provide this communication, we need a  router to implement some configuration which sets communication between two domains.In this example it will be IST1 router and we will configure “routing-instance” on it. As soon as you create this virtual router, you will create a new route table as below picture.(Route table name is same with routing-istance name, DOMAIN). Also, we will create OPSF  to communicate IST1 and ANK1 routers via OSPF.Please see below picture.

However,if we do above, IST1 inet.0 route table does not know  other OSPF domain’s route table which is inserted in DOMAIN.inet.0 route table. We have to put these route table inside of each other. First, please see below picture that there are no routes   of OSPF domain2 from Ankara1, Ankara2,Junos5 in  inet.0 route table of IST1.

Then, we will create two rib-groups  which  will be used for inet.0 and DOMAIN.inet.0. I will use SHARING and SHARING2 names for these two groups. You should remember  about matching these names to where implement.Because if you implement under protocol ospf, inet.0  has to be written before DOMAIN.inet.0  on stament rib-groups. Else, configuration check-out failed! You will understand better  by checking below picture.

After we learn rib-groups will implement respectively, we will implement SHARING under protocol ospf and SHARING2 will be implemented under routing-instance DOMAIN protocol ospf. Then, we will use first protocol ospf rib-groups SHARING command and it will provide importing inet.0 routes inside DOMAIN.inet.0  routes as you will see below picture.Keep in mind that only  ospf routes will be shared because of using  these commands under protocol ospf.

Now, after implementing  routing-instance DOMAIN protocol ospf rib-groups SHARING2, inet.0 will receive the routes of DOMAIN.inet.0

With all of these, we have provided only sharing routes on IST1 between two routing tables.Having  different routing tables is a property of junos that it separates MPLS,LDP, virtual-router route tables.Now, if you check IST1 or ANK1 routes table, you will see these routes are not recorded databases and advertised towards other routers. To provide this, we have to create  export policy. I will first export from DOMAIN towards ospf to show how databases changes in IST1 side.While exporting, I will add “tag 10” on prefixes to separete where it comes from. As you will see from below pictures, Junos6 will receive routes of DOMAIN2.

Now final step  is to advertise the routes of DOMAIN1 towards DOMAIN2. We will again create  a policy in IST1 router. I will add ” tag 20″ on prefixes which are advertised toward DOMAIN2. Please  check Junos5 route table to see routes from DOMAIN1. At the end of all configuration, we can ping from R1 router towards R2 router successfully.

I hope this article enhance your vision during OSPF working. If you need any  help or giving a suggestion, you may contact with me via “ABOUT PAGE”.

Mahmut Aydin
CCIE R&S #63405

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