The Lazy Networker

To connect two OSPF regular areas without a virtual link, you can use a GRE (Generic Routing Encapsulation) tunnel. Here’s a step-by-step guide:

Why GRE Tunnel?

A GRE tunnel allows you to encapsulate OSPF packets within a GRE header, which can be routed through a non-OSPF area. This approach eliminates the need for a virtual link.

Configuration Steps:

1. Create a GRE Tunnel:
   • Configure a GRE tunnel between the two routers that connect the two OSPF regular areas.
   • Use the tunnel mode gre ip command to create a GRE tunnel interface.
2. Configure OSPF on the GRE Tunnel:
   • Configure OSPF on the GRE tunnel interface, specifying the area ID and network type.
   • Use the router ospf command to enable OSPF on the GRE tunnel interface.
3. Configure OSPF on the Physical Interfaces:
   • Configure OSPF on the physical interfaces that connect to the GRE tunnel, specifying the area ID and network type.
   • Use the router ospf command to enable OSPF on the physical interfaces.

Example Configuration:

Suppose we have two routers, R1 and R2, that connect two OSPF regular areas, Area 1 and Area 2.

R1 Configuration:

interface Tunnel0 

tunnel mode gre 

ip tunnel source FastEthernet0/0 tunnel destination 192.168.2.2 

ip address 10.1.1.1 255.255.255.0 

router ospf 1 

network 10.1.1.0 0.0.0.255 area 1 interface FastEthernet0/0 

ip address 192.168.1.1 255.255.255.0 router ospf 1 

network 192.168.1.0 0.0.0.255 area 1

R2 Configuration:

interface Tunnel0
tunnel mode gre ip
tunnel source FastEthernet0/0
tunnel destination 192.168.1.1
ip address 10.2.2.1 255.255.255.0
router ospf 1
network 10.2.2.0 0.0.0.255 area 2

interface FastEthernet0/0
ip address 192.168.2.2 255.255.255.0
router ospf 1
network 192.168.2.0 0.0.0.255 area 2

By using a GRE tunnel, you can connect two OSPF regular areas without a virtual link. This approach provides a flexible and scalable solution for connecting multiple OSPF areas.