OSPF
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Example 2: Virtual links
In the example shown in the following figure, area 2 is not physically connected to the backbone as is
usually required. Instead, area 2 will be connected to the backbone via a virtual link through area 1. The
virtual link must be configured at each endpoint.
Figure 22 Configuring a virtual link
Configuring OSPF for a virtual link on Switch A
1. Configure IP interfaces on each network that will be attached to the switch.
In this example, two IP interfaces are needed on Switch A: one for the backbone network on
10.10.7.0/24 and one for the transit area network on 10.10.12.0/24.
>> # /cfg/l3/if 1 (Select menu for IP interface 1)
>> IP Interface 1 # addr 10.10.7.1 (Set IP address on backbone network)
>> IP Interface 1 # mask 255.255.255.0 (Set IP mask on backbone network)
>> IP Interface 1 # enable (Enable IP interface 1)
>> IP Interface 1 # ../if 2 (Select menu for IP interface 2)
>> IP Interface 2 # addr 10.10.12.1 (Set IP address on
transit area network)
>> IP Interface 2 # mask 255.255.255.0 (Set IP mask on
transit area network)
>> IP Interface 2 # enable (Enable interface 2)
2. Configure the router ID.
3. A router ID is required when configuring virtual links. Later, when configuring the other end of the
virtual link on Switch B, the router ID specified here will be used as the target virtual neighbor (nbr)
address
>> IP Interface 2 # /cfg/l3/rtrid 10.10.10.1 (Set static router ID)
4. Enable OSPF.
>> IP # /cfg/l3/ospf/on
5. Define the backbone.
>> Open Shortest Path First # aindex 0 (Select menu for area index 0)
>> OSPF Area (index) 0 # areaid 0.0.0.0 (Set the area ID)
>> OSPF Area (index) 0 # type transit (Define backbone as transit type)
>> OSPF Area (index) 0 # enable (Enable the area)
6. Define the transit area.
7. The area that contains the virtual link must be configured as a transit area
>> OSPF Area (index) 0 # ../aindex 1 (Select menu for area index 1)
>> OSPF Area (index) 1 # areaid 0.0.0.1(Set the area ID for OSPF area 1)
>> OSPF Area (index) 1 # type transit (Define area as transit type)
>> OSPF Area (index) 1 # enable (Enable the area)
