Troubleshooting Network Configuration Issues

A network administrator configures a router with the following IP address information: Gigabit Ethernet 1 Interface: 10.10.0.1/24 Serial 0 Interface: 10.10.0.253/30 Clients are connected to a switch on the gigabit Ethernet interface; the ISP is connected to the Serial 0 interface.

When the router configuration is complete and client devices are reconfigured, all clients report that they are unable to connect to the Internet.

Which of the following is the MOST likely reason?

A.

The router was configured with an incorrect IP address

B.

The router was configured with an incorrect default gateway

C.

The router was configured with an incorrect subnet mask

D.

The router was configured with an incorrect loopback address.

C.

The most likely reason for the clients being unable to connect to the Internet after the router configuration is completed is that the router was configured with an incorrect subnet mask.

To understand why this is the case, let's examine the given information in detail:

• The Gigabit Ethernet 1 interface is configured with the IP address 10.10.0.1/24. This means that the subnet mask for this interface is 255.255.255.0, which allows for a maximum of 254 hosts on this network (since the first and last addresses in the subnet are reserved for the network address and broadcast address, respectively).

• The Serial 0 interface is configured with the IP address 10.10.0.253/30. This means that the subnet mask for this interface is 255.255.255.252, which allows for a maximum of 2 hosts on this network (since the first and last addresses in the subnet are reserved for the network address and broadcast address, respectively).

Now, let's consider how the clients are connected to the network. They are connected to a switch on the Gigabit Ethernet 1 interface. This means that they are part of the 10.10.0.0/24 network and should be able to communicate with each other without any issues. However, when they try to access the Internet, they are unable to do so.

The likely reason for this is that the router's Serial 0 interface, which is connected to the ISP, is also part of the 10.10.0.0/24 network. This is because the subnet mask for this interface is incorrect. A /30 subnet mask (255.255.255.252) only allows for a maximum of 2 hosts on the network, and the addresses 10.10.0.0 and 10.10.0.255 are reserved as the network address and broadcast address, respectively. This means that the valid host addresses for this network are 10.10.0.1 and 10.10.0.2.

Since the router's Serial 0 interface is configured with the IP address 10.10.0.253/30, it is not in the same network as the clients connected to the Gigabit Ethernet 1 interface. As a result, when the clients try to access the Internet, their traffic is sent to the router, but the router does not know how to forward it to the ISP because it thinks that the clients are on a different network.

To resolve this issue, the router's Serial 0 interface should be reconfigured with a subnet mask of 255.255.255.252 and an IP address that is within the valid range for this network, such as 10.10.0.1 or 10.10.0.2. Once this is done, the router will be able to properly route traffic between the clients on the Gigabit Ethernet 1 interface and the ISP on the Serial 0 interface, and the clients should be able to access the Internet.