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A Default route is configured or learned, but is not being used - unable to reach certain subnets

Core Issue

The most common reason for this problem is that the ip classless command is turned off. Issuing the no ip classless command turns off the router's ability to look for the route with the longest bit match, as shown in this example:

ip route 10.1.1.0 255.255.255.0 1.1.1.1

ip route 0.0.0.0 0.0.0.0 2.2.2.2

no ip classless

With the no ip classless command, traffic destined to 10.2.1.1 is not sent to the default route because the class A network 10.0.0.0/8 is already in the route table.

Resolution

To have the Cisco IOS  Software forward packets destined for unrecognized subnets to the best supernet route possible, issue the ip classless command from global configuration mode, as shown in this example:

router#(config) ip classless

For more information, refer to the Enabling Classless Routing Behavior section of Configuring IP Addressing.

Version history
Revision #:
1 of 1
Last update:
‎06-22-2009 06:09 PM
Updated by:
 
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