Sunday

CCNA 2 - An assignment on VLSM


Question:

Perform subnetting with the given address 180.180.0.0/16 as the address for the following topology:

Solution:

To perform subnetting with VLSM (concerning minimal wastage of host address) we will assign network address for various lans (in the given topology) sequentially, as follows:

a. Lan 1 : 8000 hosts

b. Lan 4 : 4000 hosts

c. Lan 5 : 4000 hosts

d. Lan 2 : 2000 hosts

e. Lan 3 : 1000 hosts

f. Lan 6: 500 hosts

g. Lan 7 : 254 hosts

h. Lan 8 : 50 hosts

a. Lan 1 : 8000 hosts:

We will use base address 180.180.0.0/16 to subnet for supporting 8000 hosts. We have to borrow 3 bits from the host portion for such subnetting. There will be 23 =8 subnet each of which will have the subnet mask: 255.255.224.0.

So, Block size = (256-224) = 32 (network size).

The subnets are:

Subnet 0: 180.180.0.0/19

Subnet 1: 180.180.32.0/19

Subnet 2: 180.180.64.0/19

Subnet 3: 180.180.96.0/19

Subnet 4: 180.180.128.0/19

Subnet 5: 180.180.160.0/19

Subnet 6: 180.180.192.0/19

Subnet 7: 180.180.224.0/19

We will assign 180.180.0.0/19 (subnet 0) as the network address for lan 1.

1st valid host address for lan 1: 180.180.0.1/19.

Last valid host address for lan 1: 180.180.31.254/19.

b. Lan 4: 4000 hosts:

We will use subnet 1: 180.180.32.0/19 as the base address to subnet for supporting 4000 hosts. We have to borrow 1 bit from the host portion for such subnetting. There will be 21=2 subnets, each of which will have the subnet mask: 255.255.240.0.

So, Block size = (256-240) =16 (network size).

Subnets are:

Subnet 10: 180.180.32.0/20

Subnet 11: 180.180.48.0/20

We will assign 180.180.32.0/20 (subnet 10) as the network address for lan 4.

1st valid host address for lan 4: 180.180.32.1/20.

Last valid host address for lan 4: 180.180.47.254/20.

c. Lan 5 : 4000 hosts:

Subnet 11: 180.180.48.0/20 can support up to 212-2 = 4096-2=4094 valid hosts.

So, we will assign 180.180.48.0/20 (subnet 11) as the network address for lan 5.

1st valid host address for lan 5: 180.180.48.1/20.

Last valid host address for lan 5: 180.180.63.254/20.

d. Lan 2: 2000 hosts:

Now we will use subnet 2: 180.180.64.0/19 as the base address to subnet for supporting 2000 hosts. So, we have to borrow 2 bits from the host portion for such subnetting. There will be 22 = 4 subnets, each of which will possess the subnet mask: 255.255.254.0

So, Block size = (256-248) =8 (network size)

The subnets are:

Subnet 20: 180.180.64.0/21

Subnet 21: 180.180.72.0/21

Subnet 22: 180.180.80.0/21

Subnet 23: 180.180.88.0/21

We will assign 180.180.64.0/21 (subnet 20) as the network address for lan 2.

1st valid host address for lan 2: 180.180.64.1/21.

Last valid host address for lan 2: 180.180.71.254/21.

e. Lan 3: 1000 hosts:

we will use subnet 21: 180.180.72.0/21 as the base address to subnet for supporting 1000 hosts. So, we have to borrow 1 bit from the host portion for such subnetting. There will be 21=2 subnets, each of which will possess the subnet mask: 255.255.252.0

So, Block size = (256-252) = 4 (network size).

Subnets are:

Subnet 210: 180.180.64.0/22

Subnet 211: 180.180.72.0/22

Now, we will assign 180.180.72.0/22 (subnet 210) as the network address for lan 3.

1st valid host address for lan 3: 180.180.72.1/22.

Last valid host address for lan 3: 180.180.75.254/22.

f. Lan 6: 500 hosts:

We will use subnet 2111: 180.180.76.0/22 as the base address to subnet for supporting 500 hosts. So, we have to borrow 1 bit from the host portion for such subnetting. There will be 21=2 subnets, each of which will possess the subnet mask: 255.255.254.0

So, Block size = (256-254) = 2 (network size).

The subnets are:

Subnet 21110: 180.180.76.0/23

Subnet 21111: 180.180.78.0/23

Now, we will assign 180.180.76.1/23 (subnet 21110) as the network address for lan 6.

1st valid host address for lan 6: 180.180.76.1/23.

Last valid host address for lan 6: 180.180.77.254/23.

g. Lan 7: 254 hosts:

We will use subnet 21111: 180.180.78.0/23 as the base address to subnet for supporting 500 hosts. So, we have to borrow 1 bit from the host portion for such subnetting. There will be 21=2 subnets, each of which will possess the subnet mask: 255.255.255.0

So, Block size = (256-255) = 1 (network size).

The subnets are:

Subnet 211110: 180.180.78.0/24

Subnet 211111: 180.180.79.0/24

Now, we will assign 180.180.78.0/24 (subnet 211110) as the network address for lan 7.

1st valid host address for lan 7: 180.180.78.1/24.

Last valid host address for lan 7: 180.180.78.254/24.

h. Lan 8: 50 hosts:

We will use subnet 211111: 180.180.79.0/24 as the base address to subnet for supporting 50 hosts. So, we have to borrow 2 bits from the host portion for such subnetting. There will be 22 = 4 subnets, each of which will possess the subnet mask: 255.255.255.192.

So, Block size = (256-192) = 64 (network size).

The subnets are:

Subnet 2111110: 180.180.79.0/26

Subnet 2111111: 180.180.79.64/26

Subnet 2111112: 180.180.79.128/26

Subnet 2111113: 180.180.79.192/26

Now, we will assign 180.180.79.0/26 (subnet 2111110) as the network address for lan 8.

1st valid host address for lan 8: 180.180.79.1/26.

Last valid host address for lan 8: 180.180.79.62/26.

Network address for WAN:

We will use subnet 2111111: 180.180.78.0/24 to support 2 valid addresses. So, we have to borrow 4 bits from the host portion for such subnetting. There will be 24=16 subnets, each of which will possess the subnet mask: 255.255.255.252.

So, Block size = (256-252) = 4

a. 180.180.79.64/30

b. 180.180.79.68/30

c. 180.180.79.72/30

d. 180.180.79.76/30

e. 180.180.79.80/30

f. 180.180.79.84/30

g. 180.180.79.88/30

h. 180.180.79.92/30

i. 180.180.79.96/30

j. 180.180.79.100/30

k. 180.180.79.104/30

l. 180.180.79.108/30

m. 180.180.79.112/30

n. 180.180.79.116/30

o. 180.180.79.120/30

p. 180.180.79.124/30

We will assign:

a. 180.180.79.64/30 for network between Router A & Router B.

b. 180.180.79.68/30 network between Router B & Router C.

c. 180.180.79.72/30 network between Router A & Router C.

So, the resultant topology with network address will be:



Network address summary table:

Network Name

Network address

1st valid host

Last valid host

LAN 1

180.180.0.0/19

180.180.0.1/19

180.180.31.254/19

LAN 2

180.180.64.0/21

180.180.64.1/21

180.180.71.254/21

LAN 3

180.180.72.0/22

180.180.72.1/22

180.180.75.254/22

LAN 4

180.180.32.0/20

180.180.32.1/20

180.180.47.254/20

LAN 5

180.180.48.0/20

180.180.48.1/20

180.180.63.254/20

LAN 6

180.180.76.0/23

180.180.76.1/23

180.180.77.254/23

LAN 7

180.180.78.0/24

180.180.78.1/24

180.180.78.254/24

LAN 8

180.180.79.0/26

180.180.79.1/26

180.180.79.62/26

Network between Router A & Router B:

180.180.79.64/30

180.180.79.65/30

180.180.79.66/30

Network between Router B & Router C:

180.180.79.68/30

180.180.79.69/30

180.180.79.70/30

Network between Router A & Router C:

180.180.79.72/30

180.180.79.73/30

180.180.79.74/30















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Cisco CCNA Exploration 4.0 by Cisco CCNA Exploration 4.0 is licensed under a Creative Commons Attribution 3.0 United States License.
Based on a work at ccnaexp4.blogspot.com.