Back Panel Connection Cisco Router 1941

Cisco router has several types of ports and interfaces that are used to interconnect many other devices and other routers. For this reason, these devices have numerous types of ports and interfaces are used. Figure 1 illustrates the back panel of Cisco router 1941.  Here is the short explanation of back panel of the Cisco router 1941.

Back Pannel Explanation of Cisco Router 1941

1. These are 2 USB ports providing additional storage space similar to flash. These ports are labeled as USB 0 and USB 1.


2. These are Gigabit Ethernet interfaces. These ports generally provide LAN access by connecting to switches, other routers, and users. The ports are labeled as GE0/0 and GE0/1.


3. These ports are Auxiliary (AUX) RJ-45 ports. Auxiliary ports are being used for remote management access similar to the Console port. Now considered a legacy port because of providing support for dial-up modems.


4. These are console ports of the router which is important for initial configuration of the router. Two ports are available; the commonly used regular RJ-45 port at the left and a new USB Type-B (mini-B USB) connector at the right side at number 4. However, the console can only be accessed by one port at a time.


5. Enhanced High-speed WAN Interface Card (eHWIC)- This slot is labeled as eHWIC 0 and eHWIC 1. These ports provide modularity and flexibility by enabling the router to support different types of interface modules, including serial, digital subscriber line (DSL), switch port, and wireless.


6. Compact Flash slots labeled as CF0 and CF1 to provide increased storage flash space upgradable to 4 GB compact flash card per slot. By default, CF0 is populated with a 256 MB compact flash card and is the default boot location.

Routers CPU, OS and Memory

In chapter 1 we have already studied the general introduction of the router here we will briefly discuss routers. It is similar to a computer. Regardless of their function, size or complexity, all router models are basically computers. Just like computers, tablets, and smart devices, It also requires:

• Central processing units (CPU)


• Operating systems (OS)


• Memory consisting of random-access memory (RAM), read-only memory (ROM), nonvolatile random-access memory (NVRAM), and flash.

Here in this section, we will discuss Cisco routers. Like all computers, tablets, gaming consoles, and smart devices, Cisco devices require a CPU to execute OS instructions, such as system initialization, routing functions, and switching functions.

Central Processing Unit (CPU)

The central processing unit (CPU) of a router is a hardware that carries out the instructions of the OS to perform routing and switching.  The CPU is sometimes also referred to as the central processor unit or processor for short. The CPU generates interrupts (IRQ) in order to communicate with the other electronic components in the router.

Routers Operating System

The Cisco Internetwork Operating System (IOS) is the operating system used for most Cisco devices. Cisco IOS is a family of software used on most Cisco routers, Cisco network switches, Cisco access points and many other devices. Earlier switches run CatOS.  IOS is a package of routing, switching, internetworking and telecommunications functions integrated into a multitasking operating system. Routers Memory-Cisco router uses four types of memory which are following:

Random Access Memory(RAM)

RAM is a hardware device that allows information to be stored and retrieved on a router. This is volatile memory used in Cisco routers. This memory store application, processes, and data needed to be executed by the CPU. Cisco routers use a fast type of RAM called synchronous dynamic random access memory (SDRAM).  As we know that it is a volatile memory and requires power to keep the data accessible. If the router is turned off, all data contained in RAM is lost.RAM has following the main function:

• Store routing table.


• Running IOS.


• Store ARP Table


• Packet buffer


• Store running configuration file.

ROM

The ROM is used to start and maintain the router. This is a volatile memory of the router. It contains some code, like the Bootstrap and POST, which helps the router do some basic tests and boot up when it's powered on or reloaded. ROM is firmware embedded on an integrated circuit inside the router which can only be altered by Cisco You cannot alter any of the code in this memory as it has been set from the factory and is Read Only. ROM stores the following:

• Bootup information that provides the startup information.


• Power-on self-test (POST)


• Limited IOS to provide a backup version of the IOS. When full feature IOS has been deleted or corrupted, this limited IOS is used to restore full featured IOS.

NVRAM

This is non-volatile RAM. The NVRAM is a place where the router holds its configuration. This is the permanent memory storage of the router. When you configure a router and then save the configuration, it is stored in the NVRAM. This memory is not big at all when compared to the system's RAM. When a router starts up after it loads the IOS image it will look into the NVRAM and load the configuration file in order to configure the router. The NVRAM is not erased when the router is reloaded or even switched off.

Flash

Flash memory is non-volatile memory used as permanent storage for the IOS and other systems related files such as log files, voice configuration files, HTML files, backup configurations, and much more. When a router is rebooted, the IOS is copied from flash into RAM. The RAM is an EEPROM (Electrical Erasable Programmable Read Only Memory) card. It fits into a special slot normally located at the back of the router and contains nothing more than the IOS image. Usually, it comes in sizes of 4MB for the smaller routers and goes up from there depending on the router model.

IPv4 Router Routing Table

On a Cisco IOS router, the "show ip route" command can be used to display the router’s routing table, as shown in the figure. The show command is working in User Privilege Mode. If we want to use show commands in global configuration mode then (do) will be used before show command. The router routing table provides the following information:

• The routing information for directly-connected networks


• The routing information for remote networks.


• Information how the route was learned.


• The reliability of the route.


• Rating of the route.


• When was the route last updated?


• Which interface to use to reach the requested destination?

When a packet received at the router interface, the router read the packet header to decide the destination network for the packet. If the destination network matches a route in the routing table, then the router forwards the packet using the information in the routing table. If there are two or more possible routes to the same destination, the metric is used to make a decision which route is best.

Figure 1 shows the topology diagram which is consists of two router Rawalpindi and Peshawar. Topology in Packet Tracer can be download from here. Figure 2 shows the routing table on Rawalpindi router.

Directly Connected Routing Table Entries

When a router interface is configured with an IPv4 address and is activated with no shutdown command, the following two routing table entries are automatically created:

• C- Identifies a directly-connected network which is automatically created when an interface is configured with an IP address and activated.


• L- Identifies that this is a local interface and also show the IPv4 address of the interface on the router.

Figure 2 describes the routing table entries on Rawalpindi for the directly-connected networks 192.168.3.0, 192.168.4.0 and 192.168.10.0 These entries were automatically added to the routing table when these interfaces were configured and activated with no shutdown command. Local interface entries did not appear in routing tables previous to IOS Release 15. The IOS version of the router Rawalpindi is 12.4. so Its does not display local interface entries.

The routing table entries show that how the network was learned (C, L), the destination network for example (192.168.3.0) and outgoing interface (FastEthernet 0/0)

Remote Network Routing Table Entries

As we know that router typically has multiple interfaces configured. The routing table stores information about both directly-connected networks and remote networks. Figure 2 also shows the result of Remote Network Routing Table Entries.

The figure shows the Rawalpindi route to remote network 192.168.0.0 and 192.168.1.0. Following are the explanation of the route.

Source

Identifies how the route was learned by the router. Common routing sources include S (static route), D (Enhanced Interior Gateway Routing Protocol or EIGRP), and O (Open Shortest Path First or OSPF). Other route sources are also shown in the figure.

Destination Network

Identifies the destination network for the local router.

Administrative Distance

[90/2172416] 90 is the administrative distance of the route. It shows the trustworthiness of the router source. Lower values indicate increased the trustworthiness of the route source.

Metric

[90/2172416] The value in red show the metric of the route. Metric Identifies the value assigned to reach the remote network. Lower values indicate preferred routes.

Next-Hop

Via 192.168.10.1 is the IP address of the next router. This IP is next-hop for this route.

Route Timestamp

This is the last time when the route was updated (hours: minutes: seconds).

Outgoing interface

Last entry is the outgoing interface to use to forward a packet toward the final destination.

Router Packet Forwarding Decision

When a host going to sends a packet to another host; it will use host routing table where to send the packet. If the destination host is not on the same network, as a result the packet will be forwarded to the default gateway. When a packet arrives at the default gateway, which is generally a router. So the routers consult its routing table to decide where to forward this packet. The routing table of a router contains information about:

Directly connected routes

These routes come from the router active interfaces. Routers add a directly connected route when an interface is configured with an IP address and is activated. Each of the router's interfaces is connected to a different network segment.

Remote routes

These routes come from remote networks connected to other routers. Routes to these networks can be manually or dynamically configured on the local router by the network administrator.

Default route 

Routers also use a default route as a last option if there is no other route to the desired network in the routing table.

The figure identifies the directly connected networks and remote networks of router-1. Networks in the red rectangles are directly connected networks for router-1 and network in the blue rectangles are a remote network for router-1 and vice versa.

Downloads

Cisco Packet Tracer 6.2 Instructor version

Cisco Packet Tracer 7.0-32 Bit

Cisco Packet Tracer 7.0 – 64 bits

Putty – 64 bits

Putty – 32 bits

Wireshark - Network Analyzer

Lab - Routing Table Entries

Lab - Configuring and Verifying Router Interfaces

Lab - Identifying MAC and IP Address

Lab- Assigning IPv6 Address to Router Interfaces and Configure Static Route

Host Routing Table

On Windows host, we can check the host routing table by the help of any one of the following commands.

• route print


• netstat -r

The above mention commands can be used to display the host routing table. Both commands generate the same result. Entering the netstat -r command or the route print command displays the result which has three sections related to the current TCP/IP network connections:

Interface List

This lists show the MAC address and assigned interface number of every network-capable interface on the host, including Ethernet, Wi-Fi, and Bluetooth adapters.

IPv4 Routing Table

This show all IPv4 routes, as well as direct connections, local network, and local default routes.

IPv6 Routing Table

This show all IPv6 routes, as well as direct connections, local network, and local default routes.

The Default Gateway

The default gateway is the device that routes traffic from one network to other networks. Usually, router work as the default gateway. Which allows devices on one network to communicate with devices in another network. Therefore default simply means that this gateway is used by default unless an application specifies another gateway.

If you use the similarity that a network is like a home. The rooms in a home are like a computer in the network. The main gate of your home as just like a default gateway. If you want to get into another home then you will use the main gate of your home. Same is for a computer network; when you want to go outside from your network you will use the interface which is connected to outside networks. PC or computer that does not know the IP address of the default gateway is like a person, in a home, that does not know where the main gate is. They can talk to other people in the home or network, but if they do not know the default gateway address, or there is no gateway, then there is no way out.

The default gateway's main purpose in most homes and small offices is to direct Internet traffic from the local network to the cable or DSL modem, which connects to the Internet service provider (ISP), and vice versa. The default IP address for gateway assigned by vendors of consumer routers.

The Host Default Gateway

End device required configuration with correct IP address information, including the default gateway address of the network. The host default gateway is used when the host wants to communicate outside the network. Usually, the host default gateway address is the router interface address attached to the local network of the host. The host IP address and the router interface address should be on the same network.

A host's routing table will usually include a default gateway. The host receives the IPv4 address of the default gateway dynamically from Dynamic Host Configuration Protocol (DHCP) or configured manually. In figure 1, PCs in the local network are configured with the default gateway’s IPv4 address of 192.168.1.1. If a default getaway is configured, it creates a default route in the routing table of the PC. A default route is a route, your computer will take when it tries to contact a remote network. IPv4 address 192.168.1.1 is the address of router interface. The default route is derived from the default gateway configuration and is placed in the host computer’s routing table. In addition, all computer on the local network will have a default route to send all traffic destined to remote networks to ISP Router.

The figures 2 show a topology of a router with two networks connected with its two interfaces. FE 0/0 is connected to network 192.168.10.0/24, while FE 0/1 is connected to network 192.168.20.0/24. Each host device is configured with the right gateway address.PCs are in the same subnet, so they don’t need a gateway to communicate. It's only required destination  IP address and MAC address.

When PC1 sends a packet to PC2 on the same network, the gateway address is not used. PC1 forwards the packet directly to PC2 through the switch using the IP address of the PC-2.

If PC1 sends a packet to PC4 which is not in the same network with PC-1. In this example, PC1 addresses the packet with the IP address of the PC3, but then forwards the packet to the router. The router accepts the packet, and then accesses its routing table to decide the correct exit interface based on the destination address, and then forwards the packet out of the correct interface to reach PC4.

The Switch Default Gateway

Switch that is working in the workgroup is a layer 2 device that does not require an IP address to function properly. But, if you want to connect to the switch remotely for administration purpose over multiple networks; you will require configuring the SVI with an IPv4 address, subnet mask, and default gateway address. In other words, to remotely access the switch from another network using SSH or Telnet, the switch must have an SVI with an IPv4 address, subnet mask, and default gateway address configured. If the switch is accessed from a host within the local network; then the switch gateway address is not required. The default gateway address is necessary to configure on each device that wants to communicate beyond the local network.

The gateway address is typically the address of a router interface that is connected to switch. To configure a default gateway on a Cisco switch use the “ip default-gateway” command in global configuration mode.

Packets originating from host computers connected to the switch must already have the gateway address configured on their host computer operating systems. So they host computer do not need a default gateway configured on the switch. Actually, the IP address and default gateway information are only used for packets that originate from the switch.

Host Forwarding Decision

In a home or business network, you might have a number of wired and wireless devices interconnected each other using an intermediate device, such as a LAN switch and or a wireless access point (WAP). This intermediate device provides interconnections between local hosts on the local network. Whether a packet is destined for a local host or a remote host is determined by the IPv4 address and subnet mask combination of the source (or sending) device compared to the IPv4 address and subnet mask of the destination device.Packet forwarding between different host as the role of the network layer. A host can send a packet to the following:

Itself 

A host can ping itself by sending a packet to a special IPv4 address of 127.0.0.1, which is called a loopback address or loopback interface. Pinging the loopback interface tests the TCP/IP protocol stack on the host.

Local host 

This is a host on the same network as the sending host. The hosts share the same network address. The host can accomplish connection each other and share information without the need for any supplementary devices. If a host is sending a packet to a device that is configured with the same IP network as the host device, the packet is simply forwarded out of the host interface, through the intermediate devices, and to the destination device directly.

Remote host

This is a host on a different network. So these hosts do not share the same network address. In nearly all situations we want our devices to be able to connect beyond the local network. for example; out to other homes, businesses, and the Internet. Devices that are beyond the local network are known as remote hosts. When a source device sends a packet to a remote destination device, then the help of routers and routing is needed. Routing is the process of identifying the best path to a destination. The router connected to the local network is referred to as the default gateway. 

IPv6 Packet Header Fields

The fixed fields in the IPv6 packet header are following:

• Version - This field contains a 4-bit binary value set to 0110 that represents this as an IPv6 packet.


• Traffic Class - This 8-bit field is equivalent to the IPv4 Differentiated Services (DS) field. These 8 bits are further divided into two parts. The first 6 bits are used for Type of Service to let the Router Known what services should be provided to this packet. The last 2 bits are used for Explicit Congestion Notification (ECN).


• Flow Label - This 20-bit field suggests that all packets with the same flow label receive the same type of handling by routers.The flow label is used to keep the sequential flow of the packets belonging to a communication. The source of the packet labels the sequence to help the router identify that a particular packet belongs to a specific flow of information. This field helps avoid re-ordering of data packets. It is designed for real-time media and streaming.


• Payload Length - This 16-bit field indicates the length of the data portion of the IPv6 packet. Payload length tells the routers how much information a particular packet contains in its payload.


• Next Header - This 8-bit field is equivalent to the IPv4 Protocol field.So that field indicates either the type of Extension Header or if the Extension Header is not present then it indicates the Upper Layer PDU. The values for the type of Upper Layer PDU are same as IPv4’s




• Hop Limit- This 8-bit field replaces the IPv4 TTL field. This field is used to stop packet to loop in the network infinitely This value is decremented by a value of 1 by each router that forwards the packet. When the value reaches 0; the packet is discarded, and an ICMPv6 Time Exceeded message is forwarded to the sending host, indicating that the packet did not reach its destination because the hop limit was exceeded.


• Source Address - This 128-bit field identifies the IPv6 address of the originator host.


• Destination Address - This 128-bit field identifies the IPv6 address of the destination host.

The above mention fields are fixed for IPv6 packet header. An IPv6 packet may also contain extension headers (EH), which give optional network layer information. Extension headers are optional and are placed between the IPv6 header and the payload. Extension Header are also used for security, fragmentation, routing header, hop by hop option header, to support mobility and more.

 

Encapsulating IPv6

As earlier we discuss that IPv6 is the improved version of the internet protocol. The IPv6 header is one of the major improvements over IPv4 header. The header format has been greatly simplified for. Some of the header fields have been removed and others have been moved to the optional IPv6 Extension Header. The IPv6 header is only twice the size of the IPv4 header because the IPv6 address is 128 bit.

The IPv6 Header has greatly evolved from its IPv4 predecessor. The header of IPv6 is larger but takes up a smaller percentage of the overall header space. Some fields, for example; the Options Field and Header Checksum have been removed and replaced with improved functions in the IPv6 Extension Header. The IPv6 Header was designed to facilitate routing efficiency.

IPv6 Header Format

The improved and simplified IPv6 header as shown in Figure 1 consists of 40 octets (largely due to the 128 bit both of the source and destination IPv6 addresses) and 8 header fields (3 IPv4 basic header fields and 5 additional header fields). As painted int the figure, some fields have kept the same names as IPv4, some fields have changed names or positions, and a new field has been added.

In contrast, the IPv4 header shown in Figure 2 consists of 20 octets (up to 60 bytes if the Options field is used) and 12 basic header fields, not including the Options field.As painted in the figure, for IPv6, some fields have remained the same, some fields have changed names and positions, and some IPv4 fields are no longer required.

 

 

Introduction to IPv6 Address

In the 1990s, the IETF think about the growth of the internet and about the limitation and issues with IPv4 and began to look for an alternate. This movement led to the development of IPv6  address (IP version 6 address). IPv6 defeat the limitations of IPv4. IPv6 is a great development with features that better suit current and future network demands.

IPv6 address is the successor to the first Internet Protocol version 4. In contrast to IPv4, which defined an IP address as a 32-bit value, IPv6 addresses have a size of 128 bits. Therefore, IPv6 has a vastly enlarged address space compared to IPv4.

The 32-bit IPv4 address space provides approximately 4,294,967,296 unique addresses. on the other hand the IPv6 address space provides;  340,282,366,920,938,463,463,374,607,431,768,211,456, or 340 undecillion addresses, which is almost equivalent to each particle of sand on Earth.

IPv6 has three types of addresses, which is  following:

• Unicast addresses. A packet is delivered to one interface.


• Multicast addresses. A packet is delivered to multiple interfaces.


• Anycast addresses. A packet is delivered to the nearest of multiple interfaces.

Following are the feature that provides IPv6 address:

• Increased address space - IPv6 addresses are based on 128-bit hierarchical addressing as compare to IPv4 with 32 bits.


• Improved packet handling - The IPv6 header has to vary simply with a smaller number of fields as compared to IPv4 packet header.


• Eliminates the need for NAT – Due to a large number of public IPv6 addresses no NAT is needed. This avoids some of the NAT-induced application problems experienced by applications requiring end-to-end connectivity.

Advantages

• Increased Capacity: IPv6 increased the capacity of IP addresses and also easily accommodates additional web addresses.


• Efficient Routing: IPv6  allows for easy aggregation of prefixes assigned to IP networks. Also, reduces the size of routing tables and makes routing more efficient and hierarchical.


• More Efficient Packet Processing. IPv6's simplified packet header makes packet processing more efficient in contrast with IPv4


• Efficient Data Flow: IPv6 supports multicast rather than broadcast. Multicast allows bandwidth-intensive packet flows to be sent to several destinations simultaneously, saving network bandwidth. 


• Security: IPv6 security is improved due in part to improved authentication methods built into network firewalls.


• Simplified Network Configuration: Address auto-configuration (address assignment) is built-in to IPv6. Which makes network configuration simple.


• Support For New Services: By eliminating Network Address Translation (NAT), true end-to-end connectivity at the IP layer is restored, which enabling new and valuable services.


• Security: IPSec, which provides confidentiality, authentication and data integrity, is available in IPv6.

Disadvantages

• Conversion: IPv4 is still widely used all over the world and it is a difficult task to convert to IPv6.


• Readability:  IPv6 Subnetting can be difficult to understand. In contrast to IPv4, It will be much harder to remember the IP addresses.


• Communication: IPv4 and IPv6 equipment cannot communicate directly to each other, to communicate between IPv4 and IPv4 required more configuration.


• Transition: The process of making the switch to IPv6 from IPv4 is very slow and boring.


• IPv6 is not supported in old operating system and devices.

Limitations of IPv4 Addresses

The  IPv4 address is defined by IETF RFC 791.  RFC 791 was published in 1981. The initial design of IPv4 did not anticipate the growth of the internet and this created many issues, which proved IPv4 need to be changed. Through the years, IPv4 has been updated to address new challenges. However, IPv4 has still some major issues which are listed below.

Shortage of IPv4 Addresses

The IPv4 addressing uses 32-bit address space. This 32-bit address space is further classified into A, B, C, areD and E classes. These classes have a limited number of unique public IPv4 address which is approximately 4 billion. while there are, the increasing number of new IP-enabled devices, always-on connections, and the potential growth of less-developed regions have increased the need for more addresses.

Security Related Issues

As we discussed earlier that IPv4 was published in 1981 and the present network security issues were not projected that time. Internet Protocol Security is a protocol suite which enables network security. Internet Protocol Security provides security for IPv4 packets, but it is not built-in.

Address configuration related issues

Networks and also the internet is increasing day by day and many new computers and other devices are using IP. The configuration of IP addresses should be simple.

Internet routing table expansion

A routing table is used by routers to make the best path for communication. Because the number of servers connected to the Internet increases which also increase the number of a route. These IPv4 routes use a memory and processor resources on Internet routers.

Lack of end-to-end connectivity

NAT is a technology generally implemented within IPv4 networks. NAT makes possible to provide a way for multiple devices to share a single public IPv4 address. This can be difficult for technologies that require end-to-end connectivity. Because the public IPv4 address is shared and the IPv4 address of an internal network host is hidden.

IPv4 Packet Header

An IPv4 packet header has fields which consist important information about the packet. These fields contain binary numbers which are examined by the Layer 3 process. The binary values of each field identify various settings of the IPv4 packet. Protocol header diagrams, like the one shown in the figure, are read left to right and top down.

Important fields in the IPv4 header include

• 
  

  Version - Contains a 4-bit binary value set to 0100 that identifies this as an IP version 4 packet.

  
  


• 
  

  Internet Header Length (IHL)-  This is a 4-bit field which tells us the length of the IP header in 32-bit increments. The minimum length of an IP header is 20 bytes. The maximum value we can create with 4 bits is 15 so with 32-bit increments; that would be a header length of 60 bytes.

  
  


• 
  

  Differentiated Services (DS) - Previously called the Type of Service (ToS) field, the DS field is an 8-bit field used to determine the priority of each packet.

  
  


• 
  

  Differentiated Services Code Point (DSCP)- Usually set to 0, but may indicate particular Quality of Service needs from the network; the DSCP defines the way routers should queue packets while they are waiting to be forwarded.

  
  


• 
  

  ECN: Explicit Congestion Notification, It carries information about the congestion seen in the route.

  
  


• 
  

  Total Length: Length of entire IP Packet (including IP header and IP Payload).

  
  


• 
  

  Identification: If IP packet is fragmented during the transmission, all the fragments contain same identification number. to identify original IP packet they belong to.

  
  


• 
  

  Flags: As required by the network resources, if IPv4 Packet is too large to handle, these ‘flags’ tells if they can be fragmented or not. In this 3-bit flag, the MSB is always set to ‘0’.

  
  


• 
  

  Fragment Offset: this 13-bit field specifies the place of the fragment in the original fragmented IP packet.

  
  


• 
  

  Time-to-Live (TTL) – This field contains an 8-bit binary value that is used to limit the lifetime of a packet. The packet sender sets the initial TTL value, and it is decreased by one each time the packet is processed by a router. If the TTL field decrements to zero, the router discards the packet and sends an Internet Control Message Protocol (ICMP) Time Exceeded message to the source IP address.

  
  


• 
  

  Protocol - This 8-bit binary value indicates the data payload type that the packet is carrying, which enables the network layer to pass the data to the appropriate upper-layer protocol. Common values include ICMP (1), TCP (6), and UDP (17).

  
  


• 
  

  Header Checksum: this 16-bit field is used to store a checksum of the header. The receiver can use the checksum to check if there are any errors in the header.

  
  


• 
  

  Source IP Address - Contains a 32-bit binary value that represents the source IP address of the packet.

  
  


• 
  

  Destination IP Address - Contains a 32-bit binary value that represents the destination IPv4 address of the packet.

  
  


• 
  

  Options: This is an optional field, which is used if the value of IHL is greater than 5. These options may contain values for options such as Security, Record Route, Time Stamp, etc.

  
  

The two most commonly fields are the source and destination IP addresses. These fields identify the source and destination of the packet. Typically these addresses do not change while traveling from the source to the destination.

IP Packets - Media Independent

IP work with all type of media that bring the data at lower layers of the OSI Model. Therefore, IP packets can be travel as electrical signals over copper cable, as optical signals over fiber, or wirelessly as radio signals.

The OSI data link layer is responsible for taking an IP packet and preparing it for transmission over the communications medium. The transmission of IP packet is not limited to any particular medium. So the IP packet travels over any available transmission media.

The PDU maximum size is considered on each medium. This characteristic is called MTU (Maximum Transmission Unit). The MTU is the part of the control communication between the data link layer and the network layer. The data link layer passes the MTU value upwards to the network layer. The network layer then determines how large packets can be. When a packet is forwarding from one medium to another, in some cases, an intermediate device, split up a packet with a smaller MTU. This process is called fragmenting the packet or fragmentation

 

 

 

 

 

 

IP Data Delivery

IP protocol does not an assurance that all packets that are sent to the destination are, in fact, received. IP has unreliable data delivery. It's mean that IP does not have the ability to handle and recover from undelivered or corrupt packets. Because IP header has no such information about the location of delivery. IP header has also no information that can be processed to inform the sender whether the packet was successfully received at the destination. Packets received at the destination may be corrupted, out of sequence or not at all. IP also provides no capability for packet retransmissions if errors occur.

If the destination received in out-of-order packets, or packets are missing, upper layer helps to resolve the problem. Upper layer or application help IP to function very efficiently. In the TCP/IP protocol suite, the reliability of data transmission is the role of the transport layer.

IP Connectionless

Connectionless describes communication between two network end points in which a packet can be sent from one side to another. Connectionless means that there is no dedicated end-to-end connection before data is sent. IP connectionless is theoretically comparable to sending a letter to someone without notifying the recipient in advance. all the same; the device at one side transmits the packet to the other, without ensuring that the recipient is available and ready to receive the data. If there are problems with the transmission, it may be necessary to resend the data several times.

Connectionless data communications work on the principle where the initial exchange of control information is not required to establish an end-to-end connection before packets are forwarded. IP also does not require additional fields in the header to maintain an established connection. This process reduces the overhead of IP. But, with no pre-established end-to-end connection; senders are unaware whether destination devices are present and functional when sending packets; nor are they aware if the destination receives the packet, or if they are able to access and read the packet.

The Internet Protocol (IP) and User Datagram Protocol are connectionless protocols. These protocols are generally described as stateless because the endpoints have no protocol-defined way to remember where they are in a "conversation" of message exchanges. The alternative to the connectionless is connection-oriented protocols, which are described as stateful because they can keep track of a conversation.

Encapsulating IP

IP encapsulates the segment which is received from transport layer by adding an IP header. The header is used to carry the packet to the appropriate host. The IP header remains in packet until it arrives at the destination host.

Figure 1 illustrates how the transport layer PDU and how is then encapsulated by the network layer PDU to create an IP packet.

The process of encapsulating data, layer by layer enables the services at the different layers to grow and scale without disturbing the other layers. This means the transport layer segments can be readily packaged by IPv4 or IPv6.

Routers can apply these different network layer protocols to operate at the same time as over a network. The routing depends on only the contents of the network layer packet header. In all cases, the data portion of the packet, that is, the encapsulated transport layer PDU remains unchanged during the network layer processes.

Network Layer Protocols

There are several network layer protocols which are listed below. However, here we will discuss the first two protocols which are commonly known as IP address of the device or computer:

Network Layer Protocols list

• IPv4, Internet Protocol version 4


• IPv6, Internet Protocol version 6


• DDP, Datagram Delivery Protocol


• DVMRP, Distance Vector Multicast Routing Protocol


• ICMP, Internet Control Message Protocol


• IGMP, Internet Group Management Protocol


• IPsec, Internet Protocol Security


• IPX, Internetwork Packet Exchange


• PIM-DM, Protocol Independent Multicast Dense Mode


• PIM-SM, Protocol Independent Multicast-Sparse Mode


• RIP, Routing Information Protocol


• RSMLT Routed-SMLT

Characteristics of IP

IP was planned as a protocol with low overhead. It provides only the functions that are required to deliver a packet from a source to a destination over an interconnected network. The protocol doesn't track and manage the flow of packets. The basic characteristics of IP are following:

Connectionless

There is no connection established with the destination before sending data packets.

Best Effort

IP is inherently unreliable because packet delivery is not guaranteed.

Media Independent

The operation is dependent on the medium (i.e., copper, fiber optic, or wireless) carrying the data.

Introduction to Network Layer (Layer-3) of OSI Model

Network layer (Open System Interconnection Layer 3) specifies the packet structure and processing used to carry the data from one host to another host. Operating without regard to the data carried in each packet allows the network layer to carry packets for multiple types of communications between multiple hosts. The network layer (OSI Layer 3) provides four services to permit end devices to exchange data across the network.

Addressing end devices

 Addressing to End devices must be configured. Without a unique IP address, there is no concept of data transmission across the network. Addressing End device is necessary for identification of the devices on the network.

Encapsulation

Another important service of the network layer is to encapsulate the protocol data unit (PDU) from the transport layer (Layer 4) into a packet. The encapsulation method adds IP header information, such as the IP address of the source and destination hosts.

Routing

The network layer provides routing to direct packets to a destination host on another network. Router made it possible that the packet of one network travel to another network. The job of the router is to direct the packet to its best path toward the destination host. A packet may possibly cross many intermediary devices before reaching the destination host. Each router a packet crosses to reach the destination host is called a hop.

De-encapsulation

When the packet received at the network layer (Layer 3) of the destination host, the host checks the IP header of the packet. If the destination IP address and the IP address of the header matches. Then the IP header is removed from the packet. Removing of IP Header process is called De-encapsulation. After the packet is de-encapsulated by the network layer, the resulting Layer 4 PDU is passed upwards to layer 4 or transport layer.