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Implementing OSPF on Cisco IOS XR Software
Information About Implementing OSPF on Cisco IOS XR Software
RC-176
Cisco IOS XR Routing Configuration Guide
OL-14356-01
OSPF Hierarchical CLI and CLI Inheritance
Cisco IOS XR software introduces new OSPF configuration fundamentals consisting of hierarchical CLI
and CLI inheritance.
Hierarchical CLI is the grouping of related network component information at defined hierarchical levels
such as at the router, area, and interface levels. Hierarchical CLI allows for easier configuration,
maintenance, and troubleshooting of OSPF configurations. When configuration commands are displayed
together in their hierarchical context, visual inspections are simplified. Hierarchical CLI is intrinsic for
CLI inheritance to be supported.
With CLI inheritance support, you need not explicitly configure a parameter for an area or interface. In
Cisco IOS XR, the parameters of interfaces in the same area can be exclusively configured with a single
command, or parameter values can be inherited from a higher hierarchical level—such as from the area
configuration level or the router ospf configuration levels.
For example, the hello interval value for an interface is determined by this precedence “IF” statement:
If the hello interval command is configured at the interface configuration level, then use the
interface configured value, else
If the hello interval command is configured at the area configuration level, then use the area
configured value, else
If the hello interval command is configured at the router ospf configuration level, then use the
router ospf configured value, else
Use the default value of the command.
Tip Understanding hierarchical CLI and CLI inheritance saves you considerable configuration time. See the
“Configuring Authentication at Different Hierarchical Levels for OSPF Version 2” section on
page RC-204 to understand how to implement these fundamentals. In addition, Cisco IOS XR examples
are provided in the “Configuration Examples for Implementing OSPF on Cisco IOS XR Software”
section on page RC-255.
OSPF Routing Components
Before implementing OSPF, you must know what the routing components are and what purpose they
serve. They consist of the autonomous system, area types, interior routers, ABRs, and ASBRs.
Figure 1 illustrates the routing components in an OSPF network topology.