IPV6

Internet has been growing extremely fast so the IPv4 addresses are quickly approaching complete depletion. Although many organizations already use Network Address Translators (NATs) to map multiple private address spaces to a single public IP address but they have to face with other problems from NAT (the use of the same private address, security…). Moreover, many other devices than PC & laptop are requiring an IP address to go to the Internet. To solve these problems in long-term, a new version of the IP protocol – version 6 (IPv6) was created and developed.

IPv6 was created by the Internet Engineering Task Force (IETF), a standards body, as a replacement to IPv4 in 1998. So what happened with IPv5? IP Version 5 was defined for experimental reasons and never was deployed.

While IPv4 uses 32 bits to address the IP (provides approximately 232 = 4,294,967,296 unique addresses – but in fact about 3.7 billion addresses are assignable because the IPv4 addressing system separates the addresses into classes and reserves addresses for multicasting, testing, and other specific uses), IPv6 uses up to 128 bits which provides 2128 addresses or approximately 3.4 * 1038 addresses. Well, maybe we should say it is extremely extremely extremely huge :)

IPv6 Address Types Address Type Description Unicast One to One (Global, Link local, Site local) + An address destined for a single interface. Multicast One to Many + An address for a set of interfaces + Delivered to a group of interfaces identified by that address. + Replaces IPv4 “broadcast” Anycast One to Nearest (Allocated from Unicast) + Delivered to the closest interface as determined by the IGP A single interface may be assigned multiple IPv6 addresses of any type (unicast, anycast, multicast)

IPv6 address format Format: x:x:x:x:x:x:x:x – where x is a 16 bits hexadecimal field and x represents four hexadecimal digits. An example of IPv6: 2001:0000:5723:0000:0000:D14E:DBCA:0764 There are:
+ 8 groups of 4 hexadecimal digits. + Each group represents 16 bits (4 hexa digits * 4 bit)
+ Separator is “:” 
+ Hex digits are not case sensitive, so “DBCA” is same as “dbca” or “DBca”… IPv6 (128-bit) address contains two parts:
+ The first 64-bits is known as the prefix. The prefix includes the network and subnet address. Because addresses are allocated based on physical location, the prefix also includes global routing information. The 64-bit prefix is often referred to as the global routing prefix.

+ The last 64-bits is the interface ID. This is the unique address assigned to an interface.

Note: Addresses are assigned to interfaces (network connections), not to the host. Each interface can have more than one IPv6 address. Rules for abbreviating IPv6 Addresses: + Leading zeros in a field are optional 2001:0DA8:E800:0000:0260:3EFF:FE47:0001 can be written as 2001:DA8:E800:0:260:3EFF:FE47:1 + Successive fields of 0 are represented as ::, but only once in an address: 2001:0DA8:E800:0000:0000:0000:0000:0001 -> 2001:DA8:E800::1

Other examples: – FF02:0:0:0:0:0:0:1 => FF02::1 – 3FFE:0501:0008:0000:0260:97FF:FE40:EFAB = 3FFE:501:8:0:260:97FF:FE40:EFAB = 3FFE:501:8::260:97FF:FE40:EFAB – 0:0:0:0:0:0:0:1 => ::1 – 0:0:0:0:0:0:0:0 => ::

IPv6 Addressing In Use IPv6 uses the “/” notation to denote how many bits in the IPv6 address represent the subnet. The full syntax of IPv6 is ipv6-address/prefix-length where + ipv6-address is the 128-bit IPv6 address

+ /prefix-length is a decimal value representing how many of the left most contiguous bits of the address comprise the prefix. Let’s analyze an example: 2001:C:7:ABCD::1/64 is really 2001:000C:0007:ABCD:0000:0000:0000:0001/64

+ The first 64-bits 2001:000C:0007:ABCD is the address prefix

+ The last 64-bits 0000:0000:0000:0001 is the interface ID

+ /64 is the prefix length (/64 is well-known and also the prefix length in most cases) In the next part, we will understand more about each prefix of an IPv6 address.

OSI & TCP/IP Model

Welcome to the most basic tutorial for networker! Understanding about OSI model is one of the most important tools to help you grasp how networking devices like router, switch, PC… work.

Let’s take an example in our real life to demonstrate the OSI model. Maybe you have ever sent a mail to your friend, right? To do it, you have to follow these steps: 1. Write your letter 2. Insert it into an envelope 3. Write information about sender and receiver on that envelope 4. Stamp it 5. Go to the post office and drop it into a mail inbox

From the example above, I want to imply we have to go through some steps in a specific order to complete a task. It is also applied for two PCs to communicate with each other. They have to use a predefined model, named OSI, to complete each step. There are 7 steps in this model as listed below:

This is also the well-known table of the OSI model so you must take time to learn by heart. A popular way to remember this table is to create a fun sentence with the first letters of each layer. For example: All People Seem To Need Data Processing or a more funny sentence sorted from layer 1 to layer 7: Please Do Not Throw Sausage Pizza Away. There are two notices about this table: 1. First, the table is arranged from top to bottom (numbering from 7 to 1). Each step is called a “layer” so we have 7 layers (maybe we usually call them “layers” to make them more… technical ^^).

When a device wants to send information to another one, its data must go from top to bottom layer. But when a device receives this information, it must go from bottom to top to “decapsulate” it. In fact, the reverse action at the other end is very natural in our life. It is very similar when two people communicate via mail. First, the writer must write the letter, insert it into an envelope while the receiver must first open the envelope and then read the mail. The picture below shows the whole process of sending and receiving information.

Note: The OSI model layers are often referred to by number than by name (for example, we refer saying “layer 3” to “network layer”) so you should learn the number of each layer as well.

2. When the information goes down through layers (from top to bottom), a header is added to it. This is called encapsulation because it is like wrapping an object in a capsule. Each header can be understood only by the corresponding layer at the receiving side. Other layers only see that layer’s header as a part of data.

OSI_Model_headers_added.jpg

At the receiving side, corresponding header is stripped off in the same layer it was attached.

Understand each layer

Layer 7 – Application layer This is the closest layer to the end user. It provides the interface between the applications we use and the underlying layers. But notice that the programs you are using (like a web browser – IE, Firefox or Opera…) do not belong to Application layer. Telnet, FTP, email client (SMTP), HyperText Transfer Protocol (HTTP) are examples of Application layer.

Layer 6 – Presentation layer

This layer ensures the presentation of data, that the communications passing through are in the appropriate form for the recipient. In general, it acts as a translator of the network. For example, you want to send an email and the Presentation will format your data into email format. Or you want to send photos to your friend, the Presentation layer will format your data into GIF, JPG or PNG… format.

Layer 5 – Session layer

Layer 5 establishes, maintains and ends communication with the receiving device.

Layer 4 – Transport layer

This layer maintains flow control of data and provides for error checking and recovery of data between the devices. The most common example of Transport layer is Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

Layer 3 – Network layer

This layer provides logical addresses which routers will use to determine the path to the destination. In most cases, the logic addresses here means the IP addresses (including source & destination IP addresses).

Layer 2 – Data Link Layer

The Data Link layer formats the message into a data frame, and adds a header containing the hardware destination and source address to it. This header is responsible for finding the next destination device on a local network. Notice that layer 3 is responsible for finding the path to the last destination (network) but it doesn’t care about who will be the next receiver. It is the Layer 2 that helps data to reach the next destination. This layer is subdivide into 2 sub-layers: logical link control (LLC) and media access control (MAC). The LLC functions include: + Managing frames to upper and lower layers + Error Control + Flow control The MAC sublayer carries the physical address of each device on the network. This address is more commonly called a device’s MAC address. MAC address is a 48 bits address which is burned into the NIC card on the device by its manufacturer.

Layer 1 – Physical layer

The Physical Layer defines the physical characteristics of the network such as connections, voltage levels and timing. To help you remember the functions of each layer more easily, I created a fun story in which Henry (English) wants to send a document to Charles (French) to demonstrate how the OSI model works.

OSI_7_layers_fun.jpg

Lastly, I summarize all the important functions of each layer in the table below (please remember them, they are very important knowledge you need to know about OSI model): Layer Description Popular Protocols Protocol Data Unit Devices operate in this layer Application + User interface HTTP, FTP, TFTP, Telnet, SNMP, DNS… Data Presentation + Data representation, encryption & decryption + Video (WMV, AVI…) + Bitmap (JPG, BMP, PNG…) + Audio (WAV, MP3, WMA…) …. Data Session + Set up, monitor & terminate the connection session + SQL, RPC, NETBIOS names… Data Transport + Flow control (Buffering, Windowing, Congestion Avoidance) helps prevent the loss of segments on the network and the need for retransmission + TCP (Connection-Oriented, reliable) + UDP (Connectionless, unreliable) Segment Network + Path determination + Source & Destination logical addresses + IP + IPX + AppleTalk Packet/Datagram Router Data Link + Physical addresses

Includes 2 layers: + Upper layer: Logical Link Control (LLC) + Lower layer: Media Access Control (MAC) + LAN + WAN (HDLC, PPP, Frame Relay…) Frame Switch, Bridge Physical Encodes and transmits data bits + Electric signals + Radio signals + FDDI, Ethernet Bit (0, 1) Hub, Repeater… Note: In fact, OSI is just is a theoretical model of networking. The practical model used in modern networks is the TCP/IP model. You may think “Hm, it’s just theoretic and has no use in real life! I don’t care!” but believe me, you will use this model more often than the TCP/IP model so take time to grasp it, you will not regret – I promise :)