Consider a network with three routers R1, R2, and R3. Each router is connected w

Question

Consider a network with three routers R1, R2, and R3. Each router is connected with the two other routers. Router R1 is also connected to a subnet A, R2 is also connected to a subnet B, and R3 is also connected to a subnet C.

1. How many subnets exist in this network? (Hint: the correct answer is NOT three)

2. Assign network addresses to each subnet. All addresses must be allocated from the 214.97.254/23 address block. Subnet A should have enough addreses to support 250 interfaces. Subnet B should have enough addresses to support 120 interfaces. And Subnet C should have enough addresses to support 120 addresses. For each subnet, you should show the assigned addresses as a prefix (e.g., a.b.c.d/x). Keep in mind though that a certain subnet may use a prefix that is contained in another subnet’s prefix.

3. Based on your previous answer, show the forwarding tables for each of the three routers.

Explanation / Answer

1. six subnets.
2.Subnet A should have enough addresses to support 250 interfaces.

Number bits used for identification of host in subnet A

28-2 =256-2=254 addresses are available.(n=8)

2 addresses are used for the broad cast and subnet.

Number of bits for network: 232-n =232-8 =224 hence

Subnet A address: 214.97.254.0./24
Subnet A broad cast address: 214.97.254.255/24
  
214.97.254.11111111 /24=214.97.254.255/25

Subnet B should have enough addresses to support 120 interfaces. And

Number bits used for identification of host in subnet B

27-2 =128-2=126 addresses are available.(n=7)

2 addresses are reserved for the broad cast and subnet.

Number of bits used for network: 232-n =232-7 =225 hence

Subnet B address: 214.97.255.0/25
Subnet B broad cast address: 214.97.255.127/25
214.97.255.01111111/25=214.97.255.127/25

Subnet C should have enough addresses to support 120 addresses.

Number bits used for identification of host in subnet C

27-2 =128-2=126 addresses are available.(n=7)

2 addresses are reserved for the broad cast and subnet.

Number of bits used for network: 232-n =232-7 =225 hence

Subnet C address: 214.97.255.128/25
Subnet C broad cast address: 214.97.255.255 /25

214.97.255.11111111/25=214.97.254.255/25

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