NETW$120$ Network Review Subnet Problems

Name:

Each of the networks below has a configuration error that will prevent one or more PCs from working correctly on the network. Your task is to correct the errors in each scenario.

In the diagrams here, there are three numbers given for each NIC, in this order:

IP Address

Subnet Mask

Default Gateway

The physical default gateway for these networks is a computer, acting as a router. It's the machine at the top in these diagrams. Its default gateway address is for a second NIC, not shown, that connects to the Internet. That address is a public one.

How to Solve Subnetting Problems

Subnet Masks: Start at the Gateway Machine $($the machine at the top in these diagrams$).$ Find the subnet mask. Makersure every machine has the same subnet mask. In the example below, the subnet mask is $255\mathrm{.}255\mathrm{.}255\mathrm{.}0$

Label the subnet: Find the network portion of the IP address of the Gateway Machine. Fill in the host portion with Os$.$ Write that label above the network $($in the upper left, in these diagrams$).$ In the example below, the Gateway Machine has an IP address of $192\mathrm{.}168\mathrm{.}1\mathrm{.}101$ and since the subnet mask is $255\mathrm{.}255\mathrm{.}255\mathrm{.}0,$ the network portion includes only the first $3$ octets. To find the subnet label, replace the last octet with zero: $192\mathrm{.}168\mathrm{.}1\mathrm{.}0).$

Check the IP Addresses

Network Portion: Make sure that each NIC on a subnet has the same network address as the label you wrote at the top of the subnet. In the example below, on the left subnet, that means every $IP$ address must start with $192\mathrm{.}168\mathrm{.}1$

Host Portion: Make sure that each NIC on a subnet has a different host address, including the default gateway. In the example below, the Gateway Machine has a host address of $1,$ and the others are $101,102,$ and $103,$ so there are no duplicates.

Default Gateway: On each subnet, a PC is serving as a routeridefault gateway. The default gateway for the network is the Gateway Machine's IP address. It is the same for each NIC on the subnet, except the Gateway Machine itself, which has a default gateway of the network above it$.$ usually an ISP. In the example below, the Gateway Machine has an IP address of $192\mathrm{.}168\mathrm{.}1\mathrm{.}1,$ so the default gateway must be $192\mathrm{.}168\mathrm{.}1\mathrm{.}1$ for all three workstations at the bottom of the chart:

Subnet: $192\mathrm{.}168\mathrm{.}1\mathrm{.}0$

Internet

Fill in the missing numbers so all PCs on this network will operate correctly.

Subnet:

To the Internet