Configuring OSPF
Configuring OSPF
page 1-22
OmniSwitch AOS Release 7 Advanced Routing Configuration Guide
March 2011
Creating Virtual Links
A virtual link is a link between two backbones through a transit area. Use the
ip ospf virtual-link
command to create or delete a virtual link.
Accepted network design theory states that virtual links are the option of last resort. For more information
on virtual links, see
“Virtual Links” on page 1-9
and refer to the figure on
page 1-9
.
Creating a Virtual Link
To create a virtual link, commands must be submitted to the routers at both ends of the link. The router
being configured should point to the other end of the link, and both routers must have a common area.
When entering the
ip ospf virtual-link
command, it is necessary to enter the Router ID of the far end of
the link, and the area ID that both ends of the link share.
For example, a virtual link needs to be created between Router A (router ID 1.1.1.1) and Router B (router
ID 2.2.2.2). We must:
1
Establish a transit area between the two routers using the commands discussed in
“Creating an OSPF
Area” on page 1-16
(in this example, we will use Area 0.0.0.1).
2
Then use the
ip ospf virtual-link
command on Router A as shown:
-> ip ospf virtual-link 0.0.0.1 2.2.2.2
3
Next, enter the following command on Router B:
-> ip ospf virtual-link 0.0.0.1 1.1.1.1
Now there is a virtual link across Area 0.0.0.1 linking Router A and Router B.
4
To display virtual links configured on a router, enter the following
show
command:
-> show ip ospf virtual-link
5
To delete a virtual link, enter the
ip ospf virtual-link
command with the area and far end router infor-
mation, as shown:
-> no ip ospf virtual-link 0.0.0.1 2.2.2.2
Modifying Virtual Link Parameters
There are several parameters for a virtual link (such as authentication type and cost) that can be modified
at the time of the link creation. They are described in the
ip ospf virtual-link
command description. These
parameters are identical in function to their counterparts in the section
“Modifying Interface Parameters”
on page 1-21
.
Using Route Maps
A route map specifies the criteria that are used to control redistribution of routes between protocols. Such
criteria is defined by configuring route map statements. There are three different types of statements:
•
Action
. An action statement configures the route map name, sequence number, and whether or not
redistribution is permitted or denied based on route map criteria.
•
Match.
A match statement specifies criteria that a route must match. When a match occurs, then the
action statement is applied to the route.
