Examine the following FIB table:
Which of the following statements is NOT true?
A. These are the default entries in an FIB table
B. No IP addresses have been configured on this router
C. Multicast routing is enabled
D. The gateway of last resort has not been set
Explanation:
The Forwarding Information Base (FIB) table is created when Cisco Express Forwarding (CEF) is enabled on the router. FIB is a mapping of destination networks and IP addresses to next-hop IP addresses and exit interfaces.
In the scenario, multicast routing has NOT enabled in the router. If it were enabled, the next hop for the 224.0.0.0/4 network would not be listed as drop. A drop means any packets sent to multicast IP addresses will be dropped. If multicast routing were enabled, the entry for 224.0.0.0 would appear as follows:
Prefix Next Hop Interface
224.0.0.0/4 0.0.0.0
The next hop of 0.0.0.0 means that this traffic will be process switched, and CEF cannot forward the packets.
The table displayed in the scenario contains the default entries in the FIB. These entries will change based on further configuration of the router interfaces and the addition of routes to the routing table through either static routing or through routing protocols.
No IP addresses have been configured on the router. Had they been configured, the addresses of the networks to which they were connected would be in the table. For example, if the IP address of the FastEthernet 0/1 interface were set to 192.168.1.1/24, three entries would have been added to the table as follows:
While the first IP address represents the directly attached network of which the interface is a member, the second IP address represents the network ID of the network, the third IP address represents the specific IP address assigned to the interface, and the last IP address represents the broadcast address of the network.
The gateway of last resort has not been set on the router. If it were set, it would be listed along with an IP address for the next hop and the exit interface. An entry for a gateway of last resort (or default route) would resemble the following:
Prefix Next Hop Interface
0.0.0.0/0 192.168.5.5 FastEthernet 0/0
Objective:
Network Principles
Sub-Objective:
Identify Cisco Express Forwarding concepts