Cisco Systems 78-11741-02 Wireless Office Headset User Manual


 
Configuring OSPF
Configuring Lookup of DNS Names
IPC-232
Cisco IOS IP Configuration Guide
Configuring Lookup of DNS Names
You can configure OSPF to look up Domain Naming System (DNS) names for use in all OSPF show
EXEC command displays. This feature makes it easier to identify a router, because the router is
displayed by name rather than by its router ID or neighbor ID.
To configure DNS name lookup, use the following command in global configuration mode:
Forcing the Router ID Choice with a Loopback Interface
OSPF uses the largest IP address configured on the interfaces as its router ID. If the interface associated
with this IP address is ever brought down, or if the address is removed, the OSPF process must
recalculate a new router ID and resend all its routing information out its interfaces.
If a loopback interface is configured with an IP address, the Cisco IOS software will use this IP address
as its router ID, even if other interfaces have larger IP addresses. Because loopback interfaces never go
down, greater stability in the routing table is achieved.
OSPF automatically prefers a loopback interface over any other kind, and it chooses the highest IP
address among all loopback interfaces. If no loopback interfaces are present, the highest IP address in
the router is chosen. You cannot tell OSPF to use any particular interface.
To configure an IP address on a loopback interface, use the following commands beginning in global
configuration mode:
Controlling Default Metrics
In Cisco IOS Release 10.3 and later releases, by default OSPF calculates the OSPF metric for an
interface according to the bandwidth of the interface. For example, a 64-kbps link gets a metric of 1562,
while a T1 link gets a metric of 64.
The OSPF metric is calculated as the ref-bw value divided by the bandwidth value, with the ref-bw value
equal to 10
8
by default, and the bandwidth value determined by the bandwidth interface configuration
command. The calculation gives FDDI a metric of 1. If you have multiple links with high bandwidth,
you might want to specify a larger number to differentiate the cost on those links. To do so, use the
following command in router configuration mode:
Command Purpose
Router(config)# ip ospf name-lookup
Configures DNS name lookup.
Command Purpose
Step 1
Router(config)# interface loopback 0
Creates a loopback interface, which places the router
in interface configuration mode.
Step 2
Router(config-if)# ip address ip-address mask
Assigns an IP address to this interface.
Command Purpose
Router(config-router)# auto-cost reference-bandwidth
ref-bw
Differentiates high bandwidth links.