Monavathia's Blog

CCNA 2 Labskill Chapter 4

Posted on: November 22, 2010

Lab 4.1.5 Subnetting a Network


•  Create an IP addressing plan for a small network.

Background / Preparation

In this activity, you will play the role of an onsite installation and support technician from an ISP.  A customer has called the ISP complaining of e-mail problems and occasional poor Internet performance. On an earlier site visit, the technician had created diagram of the customer’s existing network shown here.  The ISP is preparing a design for a network upgrade. The interim topology diagram for the proposed network is shown below. There is still a requirement for an IP addressing plan. One of the ISP network designers has made some notes on a simplified sketch of the proposed network, and has written some requirements. The designer asks you to create an IP address plan for the network upgrade.

Step 1: Analyze the network

a.  Referring to the Rough Design Notes, determine the minimum number of hosts that a subnet needs to support the new network design.

1)  The largest subnet must be able to support 30 hosts.

2)  To support that many hosts, the number of host bits required is?

Jawaban = dari 30 host maka jumlah subnet bit yang dibutuhkan adalah sebanyak 3 buah.

b.  What is the minimum number of subnets required for the new network design?

Jawaban= jumlah minimum subnet yang dibutuhkan membangun sebuah jaringan yaitu sebanyak 5-8 segmen jaringan ( jumlah subnet).

c.  Can this network be subnetted according to the requirements?

Jawaban = ya, jaringan ini bisa dilakukan subnetting.

For example: If four subnets are required and the largest subnet has to support 128 hosts, this is a problem, because a subnet in a class C network that has been partitioned four ways can support only 62 hosts.

d. Fill in the blanks to summarize the subnetting requirements of this new network design:

This network requires 129-256 subnets, each supporting 29 hosts. Therefore, host ID bits are reserved for the subnet ID. With those values, this network supports  subnets 8, each subnet having 254 hosts.

Step 2: Calculate the custom subnet mask

Now that the number of subnet ID bits is known, the subnet mask can be calculated. A class C network has a default subnet mask of 24 bits, or What will the custom subnet mask be? The custom subnet mask for this network will be or /25.

Step 3: Specify the host IP addresses

Now that the subnet mask is identified, the network addressing scheme can be created. The addressing scheme includes the subnet number, the subnet broadcast address, and the range of IP addresses assignable to hosts.

a.  Complete the table showing all the possible subnets for the network.

Subnet Subnet Address Host IP Address Range Broadcast Address

b. for it to be completed. Hosts will be assigned IP addresses as follows: (fill in the table below)

Device Interface IP Address Connects to IP Address
1841 Serial 0/0/0 ISP Router
Fa 0/0 Wired hosts Wired host Range:____.____.____.____To 


Fa 0/1 Linksys Internet
Linksys Internet 1841 Fa 0/1
LAN Gateway Wireless Hosts Wireless host Range:____.____.____.____To 


Step 4: Consider other subnetting options

What if there were more than 30 hosts that needed to be supported on either the wired or wireless portion of the network. You could borrow fewer bits, which would create fewer subnets, but each one would support a greater number of hosts per subnet.

a. How many bits would be borrowed to create four subnets?


adalah 2  buah bit yang akan dipinjam

b. How many bits would be left for hosts on each subnet?


5 sampai 8 bits

c. What is the maximum number of hosts each subnet could support?


30 host – 2broadcast = 28 host

d. What would the subnet mask be in dotted decimal and slash number (/#) format?

Jawab: atau / 27

d. If you start with the same network as before and subnet it into four subnets, what would the subnet numbers be?

Jawab: –

Step 5: Reflection

a.  Does subnetting help reduce the problem of IP address depletion? Explain your answer.


Iya, sangat membantu mengurangi masalah depletions pada IP address, karena bisa membedakan network identifier dengan host identifier.

b. The Rough Design Notes diagram noted that the wireless subnet would have up to 30 PCs connecting. In pairs or in small groups, discuss whether or not that creates a situation in which IP addresses might get wasted. Does it matter, and why or why not?


Akan sia sia karena proses subnetting yang menghasilkan beberapa subjaringan dengan jumlah host yang sama telah dilakukan, maka aka nada kemungkinan di dalam segmen –segmen jaringan tersebut memiliki alamat – alamat yang tidak digunakan.

c. There are alternate methods of subnetting using CIDR and VLSM. Would VLSM be a worthwhile option for subnetting this network? Discuss in small groups


vlsm bisa menjadi solusi karena teknik subnetting dengan VLSM dapat dilakukan secara rekrusif : network identifier yang sebelumnya telah disubnetkan, di subnetkan kembali . maka dengan kata lain pengambilan kembali sisa dari bit- bit host.

Lab 4.2.4 Determining PAT Translations

  1. Client on a private network sends a request to a web server on the public Internet.
  2. N A T  router translates source address and forwards the request to the web server
  3. T h e web server responds to the client’s translated address
  4. The N A T router translates the client address ( destination)  back to the original private address


  • Explain the active network connections open on a computer when viewing a particular web page.
  • Determine what an internal IP address and port number are translated to using port address.

Background / Preparation

Port address translation (PAT) is a form of network address translation ( N A T ) .With PAT, the router. translates multiple internal ( usually private) addresses to a single public IP address on an interface that is connected to the Internet. Port numbers are used, in combination with IP addresses, to keep track of individual connections. In this lab, you use the ipconfig and netstat commands to view open ports on a computer. You will be able to see the initial IP address and port combination, and determine the translated  IP address and port combination The following resources are required:

  • Computer running Windows XP Professional.
  • Connection to a gateway router or an  I S R  using  P A T.
  • Internet connection.
  • Access to the PC command prompt.

Step 1: Determine the IP address of the computer

Open a Command  Prompt window by clicking Start  >  Run and typing cmd. Alternatively, you may click Start  >  All  programs  >  Accessories >  Command Prompt. At the prompt, type the ipconfig command to display the IP address of the computer.

a. What is the IP address of the computer?


b. Is  there a port number shown, and why or why not?


Ya, ada port number yang muncul, hal ini karena access point telah dikelompokkan atau dibagi dalam beberapa titik akses, sehingga memiliki default gateway yaitu

Step 2 : Determine the IP addresses of the gateway router or ISR

Check with your instruct or to get the IP addresses for the ISR NAT router gateway.

Internal Ethernet Address :

External Internet Address :

Step 3 : Display base line netstat results.

a. At  the command  prompt, type the netstat  –n command.

b. What  type of information does the netstat  –n command  return?


Protocol, IP address, Foreign address.

c. Where does the IP address found in Step 1 appear? Is there a port number associated with it? Why or why not?


Ya ditemukan, karena menggunakan port gateway.

Step 4 : Display active network connections

a. Ping and record the address.

b. Open a web browser and enter in the address bar.

c. Go back to the Command Prompt Window. Type the netstat –n command again, and then  type the command without the – n option. The output looks similar to the following figure, depending on what other network applications and connections are open when you issued the command.

d. What is the difference in the output between the netstat and netstat – n commands?


Perbedaannya ialah pada netstat –n hanya menampilakan informasi dari address local ke foreign address. Sedangkan netstat tampa –n akan menapilakn informasi secara details mulai dari ip address, alamat protocol yang digunakan, lokasi isp. Dan user.

e. Write down the connection entries for the client IP address and the IP address of the web server.

Local client IP address and port number : Foreign IP address and port number : :1227 :1228 :1228 :1227 :1229 :1230 :80 :53

f. Are there more netstat entries the second time?


Tidak ada lagi perintah nestat yang berbeda meskipun untuk pengulangan kedua kalinya.


a. Port address translation (PAT) is also called NAT with overload. What does the term “overload” refer to?


overload merupakan istilah ditujukan pada IP address karena pada nat overload bukan hanya satu alamat ip public yang terekspos,bisa lebih dari satu jika berupa overload.

b. The NAT terminology used in the lab includes four type of address: Inside-local, inside-global, outside-local, and outside-global. In many connections that pass through NAT routers, two of these address are often the same. Which two of these four addresses normally remain unchanged, and why do you think that is the case?


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