TCP/IP Addressing and IPv6
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[edit section] TCP/IP Addressing and IPv6
The Network+ exam will contain a few questions on TCP/IP IPv4 addressing, which is a fairly simple subject matter to master and will earn you some easy points. It is therefore recommended that you understand what an IP address is and how the numbering of the IP address reveals network information.
[edit section] The IPv4 Address
An IPv4 Address, often shortened to “IP Address,” is a numeric identifier of a network node that uniquely identifies that node either on a LAN or on the wider Internet. Therefore, if two nodes on a network use the same IP address, a conflict will occur as the IP address reflects a “one-to-one” relationship between hardware and logical address. As a result, neither of the two nodes with duplicate addresses will receive full communications.
The IP address is 32-bit number comprised of four octets ranging from 0 to 255, or 256 numbers (numbers that range from 0 to 2^8-1, hence the term "octet"). Given this, there are a limited number of IP addresses – at maximum, 256^4 or 4,294,967,296. This number is inflated because certain IP addresses are reserved or unavailable. Given the rate of growth that the Internet is currently experiencing, it is widely recognized that 4 billion IP addresses will not be enough to compensate for all of the nodes of the world. It is for this reason that many advocate changing to IPv6, which is 128 bits and utilizes hexadecimal (base 16), rather than octal (base 8), numbers. IPv6 will be covered briefly later. What you should know is that although IPv6 is superior in many ways to IPv4, IPv4 is the most commonly used protocol for now and so is the one tested on the Network+ exam.
The IP address is comprised of two parts: the netid and the hostid. The netid indicates the network that a node is on while the hostid indicates the actual, specific node. The number of octets dedicated to the netid varies based on the first number of the network. Actually, that first number tells you quite a bit. The first number determines the size (Class) of the network and therefore both the number of octets dedicated to the "netid" and the number dedicated the "hostid". Below is a table of the first octet numbers and information about their classes:
| Class | First Octet Range | Example | Default Subnet | Typical Application |
| A (netid . hostid . hostid . hostid) | 1-126 | 17.14.22.211 | 255.0.0.0 | University Network System |
| B (netid. netid. hostid. hostid) | 128-191 | 143.144.1.1 | 255.255.0.0 | Corporate System or Hospital Network |
| C (netid. netid. netid. hostid) | 192-223 | 204.213.288.222 | 255.255.255.0 | Small Business, Home Internet Connection |
If you noticed, there is a column above for “Default Subnet.” Subnetting is a feature of TCP/IP whereby networks can be subdivided, creating “logical networks” within a given network. This allows one, in effect, to create multiple networks on a single IP network by routing the subnets (nodes connect via a default gateway which can find the router) necessary for communication with other logical networks.
Note that there are some “reserved” IP address ranges:
| Range | Purpose |
| 127.0.0.0 – 127.255.255.255 | Loopback (returns the node that requests it) |
| 10.0.0.0 – 10.255.255.255 | Private Network (Class A) |
| 172.16.0.0 - 172.31.255.255 | Private Network (Class B ) |
| 192.168.0.0 – 192.168.255.255 | Private Network (Class C) |
(255.255.255.255 is reserved as a “Broadcast” address, which sends information to all nodes on the same network)
Often times, a connection (through a router) to the Internet may be shared by multiple computers, which raises the question: What IP addresses do the computers that connect to the Internet through the router take? Actually, they are assigned a “private” IP address in one of the above reserved ranges for communication within the LAN; external communication is all channeled through the single “wide” IP address. This is called Network Address Translation and don’t worry about it for now – we’ll cover it later.
[edit section] IPv6
IPv6 is an emerging technology that is coming into networking as the IPv4 address space is being exhausted. It differs from IPv4 in several important ways, first it is 128 bits instead of 32 bits, it is written in hexadecimal instead of decimal, and bytes are seperated by colons instead of periods.
With those considerations we can write an IPv6 address as such:
0000:0000:0000:1aff:1923:ab00:0000:22a1:3712:0000:0000:0000:acc2:32aa:8eff:bf00
Obviously this is an unwieldy number for networking so the authors of IPv6 gave us some shortcuts to help us out. First a double colon can be used to symbolize long strings of zeroes in an address but only once for each address. For example, the previous address could be written as:
::1aff:1923:ab00:0000:22a1:3712:0000:0000:0000:acc2:32aa:8eff:bf00
or
0000:0000:0000:1aff:1923:ab00:0000:22a1:3712::acc2:32aa:8eff:bf00
but not
::1aff:1923:ab00:0000:22a1:3712::acc2:32aa:8eff:bf00
as the computer would have no way of knowing how long each block of zeroes actually is thus rendering the address unreadable.
Additionaly consecutive zeroes can be expressed as a single 0. So our previous address would be correctly expressed as:
::1aff:1923:ab0:0:22a1:3712:0:0:0:acc2:32aa:8eff:bf0
While still far longer than an IPv4 address you can see that this is much more manageable.
The authors did us another favor and created a new loopback address. Rather than losing an entire range of addresses as they did in IPv4, the IPv6 loopback is ::1.
This should cover everything you need to know about IPv6 for the Network+ exam. However, as a network technician you should remember that it is an emerging technology, at some point you will have to work with it, and you should keep up with, and eventually know it as well as IPv4.
[edit section] Practicing What You Preach
Now, here are a few sample problems that should help you jog your knowledge on IP addressing.
1. A network has nodes on IP’s ranging from 143.144.12.0 to 143.144.12.222. The router on this network is at 143.144.12.1. The IP address of Node A is 143.144.12.27. What is the default gateway for Node A?
A. 255.255.0.0
B. 127.0.0.1
C. 143.144.12.27
D. 143.144.12.26
E. 143.144.12.1
2. Which of the following is a valid public Class A IP address?
A. 127.143.22.22
B. 10.41.55.16
C. 0.4.0.3
D. 123.2.15.15
E. 166.44.13.12
3. Which of the following is a not a possible subnet mask?
A. 255.0.0.0
B. 255.255.0.0
C. 255.255.252.0
D. 255.255.255.0
E. 255.255.255.255
4. Which of the following is a valid IPv4 address?
A. 4:AC:AD:34
B. 266.144.13.3
C. 244.233.12.1
D. 10:0:0:1
E. 10:0:0:A
5. You install and configure a new computer. In doing this, you add the new computer to your IP-based network and assign it an IP address. After restarting, you notice that the connection to the network is sporadic; in addition, another user calls you and complains that his network connection is not functioning. What is the most likely explanation?
A. You configured the wrong default gateway
B. You configured a duplicate IP address
C. You used a unique IP address
D. You configured a duplicate subnet address
E. You used a unique subnet address
[edit section] Answers
1. The default gateway for a node is the same as the router that connects the node to the other subnets on the entire LAN; therefore, because the router is 143.144.12.1, the default gateway is 143.144.12.1. The answer is (E)
2. Review the table to see the ranges for valid Class A IP addresses. Note that although ([[Image:|user posted image]] is in the range 1-126, 10.x.x.x is reserved for private Class A networks. Therefore (D) is the correct answer.
3. All of the above are possible except for (E), which is reserved as the broadcast address. Note that answer C is a possible subnet address.
4. IP addresses are four octets (numbers within 0-255, normally 1-254) separated by periods. The only choice that satisfies this is choice C
5. After adding the new PC to the network, neither the new PC nor the complaining user’s PC is receiving full service. The only way that the new PC would affect the user’s PC is if the new PC is using a duplicate IP address, which would deny service to either. Therefore the answer is B.
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