CCNA 1 v3.0 Module 9 TCP/IP Protocol Suite and IP Addressing

Objectives

Introduction to TCP/IPInternet addressesObtaining an IP address

Introduction to TCP/IP

History and Future of TCP/IP

The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions.Some of the layers in the TCP/IP model have the same name as layers in the OSI model.

Application Layer

Handles high-level protocols, issues of representation, encoding, and dialog control. The TCP/IP protocol suite combines all application related issues into one layer and ensures this data is properly packaged before passing it on to the next layer.

Application Layer Examples

Transport Layer

Five basic services:Segmenting upper-layer application dataEstablishing end-to-end operationsSending segments from one end host to another end hostEnsuring data reliabilityProviding flow control

Definition

Relaible/ UnreliableIP is sometimes referred to as an unreliable protocol. This does not mean that IP will not accurately deliver data across a network. Calling IP an unreliable protocol simply means that IP does not perform error checking and correction. That function is handled by upper layer protocols from the transport or application layers.

Transport Layer Protocols

TCP and UDP

TCP and UDP Segmenting upper-layer application data Sending segments from one end device to another end device

TCP only Establishing end-to-end operations Flow control provided by sliding windows Reliability provided by sequence numbers and acknowledgments

Internet LayerThe purpose of the Internet layer is to send packets from a network node and have them arrive at the destination node independent of the path taken.

IP

IP performs the following operations: Defines a packet and an addressing scheme Transfers data between the Internet layer and network access layers Routes packets to remote hosts

Network Access LayerThe network access layer is concerned with all of the issues that an IP packet requires to actually make a physical link to the network media.It includes the LAN and WAN technology details, and all the details contained in the OSI physical and data link layers.

Comparing the OSI Model and TCP/IP Model

Similarities of the OSI and TCP/IP Models Both have layers.Both have application layers, though they include very different services.Both have comparable transport and network layers. Packet-switched, not circuit-switched, technology is assumed.Networking professionals need to know both models.

Differences of the OSI and TCP/IP Models TCP/IP combines the presentation and session layer into its application layer.TCP/IP combines the OSI data link and physical layers into one layer. TCP/IP appears simpler because it has fewer layers.TCP/IP transport layer using UDP does not always guarantee reliable delivery of packets as the transport layer in the OSI model does.

Internet Architecture

Two computers, anywhere in the world, following certain hardware, software, protocol specifications, can communicate, reliably even when not directly connected. LANs are no longer scalable beyond a certain number of stations or geographic separation.

Internet Architecture

The OSI models goal is to build the functionality of the network in independent modules. This allows a diversity of LAN technologies at Layers 1 and 2 and a diversity of applications functioning at Layers 5, 6, and 7.Not all networks are directly connected to one another. The router must have some method to handle this situation.

A router to keep a list of all computers and all the paths to them. The router would then decide how to forward data packets based on this reference table. The forwarding is based on the IP address of the destination computer. This option would become difficult as the number of users grows. Scalability is introduced when the router keeps a list of all networks, but leaves the local delivery details to the local physical networks. The routers pass messages to other routers. Each router shares information about which networks it is connected to. This builds the routing table.

Internet Addresses

IP AddressingAn IP address is a 32-bit sequence of 1s and 0s.To make the IP address easier to use, the address is usually written as four decimal numbers separated by periods. This way of writing the address is called the dotted decimal format.

IP addressing

An IP address is a 32-bit sequence of 1s and 0s. The IP address is broken down into two parts the network portion and the host portion. IP addresses were originally divided into three main classes A, B and C. Class A addresses are assigned to larger networks. Class B addresses are used for medium-sized networks, and Class C for small networks

IPv4 Addressing

Class A, B and C

In Class A address the fist octet (8 bits) defines the network number the other three define host ID, this means up to 126 Class A networks are possible each hosting up to 16m hosts.Class B addresses, the first and second octets are defined as the network number and the third and forth as the host number, this means there are 16,000 class B addresses which can have 65000 hosts. In class C addresses only the forth octet is assigned to the network number, each of 2,000,000 class C addresses can host 254 hosts.

Reserved IP Addresses Certain host addresses are reserved and cannot be assigned to devices on a network. An IP address that has binary 0s in all host bit positions is reserved for the network address. An IP address that has binary 1s in all host bit positions is reserved for the network address.

Public and Private IP Addresses No two machines that connect to a public network can have the same IP address because public IP addresses are global and standardized. However, private networks that are not connected to the Internet may use any host addresses, as long as each host within the private network is unique. RFC 1918 sets aside three blocks of IP addresses for private, internal use. Connecting a network using private addresses to the Internet requires translation of the private addresses to public addresses using Network Address Translation (NAT).

Introduction to Subnetting To create a subnet address, a network administrator borrows bits from the host field and designates them as the subnet field.

IPv4 versus IPv6

IP version 6 (IPv6) has been defined and developed. IPv6 uses 128 bits rather than the 32 bits currently used in IPv4. IPv6 uses hexadecimal numbers to represent the 128 bits.

IPv4

Obtaining an IP Address

Obtaining an Internet AddressStatic addressing Each individual device must be configured

with an IP address.Dynamic addressing Reverse Address Resolution Protocol (RARP) Bootstrap Protocol (BOOTP) Dynamic Host Configuration Protocol (DHCP) DHCP initialization sequence Function of the Address Resolution Protocol ARP operation within a subnet

How does a computer get its IP address?

1) Static: given to it by the administrator2) Dynamic

RARP (reverse address resolution protocol) – the computer sends out a broadcast and the RARP server responds with an IP addressBOOTP (BOOTstrap Protocol) similar to RARP but the bootp server returns other information, BOOTP datagrams can include the IP address, the address of a router (default gateway), the address of a server, and a vendor-specific field.

Both RARP and Bootp use a static table of MAC and IP addresses.

DHCP – Dynamic host connection protocol

DHCP – Dynamic host connection protocolHost sends request for IP address for DHCP serverServer responds with offer and lease timeHost replies with acknowledgementServer acknowledges IP assignment

DHCP

A DHCP service can be created on a server, the user tells the server the range of IP addresses it can give out e.g. 200.20.50.4 – 200.20.50.55. The user also tells the service how long a host can keep this address either indefinitely or for days/weeks/sessions. This is often used for computers not in use all the time, therefore the IP addresses are not permanent.

BOOTP IP

The Bootstrap Protocol (BOOTP) operates in a client/server environment and only requires a single packet exchange to obtain IP information.BOOTP packets can include the IP address, as well as the address of a router, the address of a server, and vendor-specific information.

Dynamic Host Configuration Protocol

Allows a host to obtain an IP address using a defined range of IP addresses on a DHCP server.As hosts come online, contact the DHCP server, and request an address.

Problems in Address Resolution In TCP/IP communications, a datagram on a local-area network must contain both a destination MAC address and a destination IP address. There needs to be a way to automatically map IP to MAC addresses.The TCP/IP suite has a protocol, called Address Resolution Protocol (ARP), which can automatically obtain MAC addresses for local transmission. TCP/IP has a variation on ARP called Proxy ARP that will provide the MAC address of an intermediate device for transmission outside the LAN to another network segment.

Address Resolution Protocol (ARP) Each device on a network maintains its own ARP table.A device that requires an IP and MAC address pair broadcasts an ARP request. If one of the local devices matches the IP address of the request, it sends back an ARP reply that contains its IP-MAC pair. If the request is for a different IP network, a router performs a proxy ARP. The router sends an ARP response with the MAC address of the interface on which the request was received, to the requesting host.

The users computer builds the packet and then a frame (needs the destination and source MAC address)Each computer knows its own MAC address (build into NIC card)A packet must be enclosed in a frame if it is to be transmittedAll frame headers for LANs require a destination MAC addressARP is used to locate an unknown destination MAC address.

The following method is used.

1. Destination IP address is checked using the subnet mask to see if the destination is on the same network/ subnet as the source.

2. The ARP table is checked, this contains a list of IP addresses and their corresponding MAC addresses.

3. If entry is present in the ARPtable the destination MAC address is used in the frame and the frame is sent.

4. If entry is not present then an ARP request is broadcast.

5. The ARP request contains the destination and source IP address and the source IP address and the broadcast IP address as destination (48 binary 1s or 12 F hex)

6. All hosts on the same segment open the frame since it is addressed to all computers. The host with a matching address will return an ARP reply containing its MAC address.

7. All other computers update their ARPtables with sender’s MAC address and IP address.

8. When sender receives the ARP reply it records the details in its ARPTable and then send the frame.

Note

If the initial check in step 1 indicates that the destination computer is on a different network/ subnet then the frame must be sent to the default gateway (the router).The destination IP address will always identify the computer we want to talk to (not the router) the destination MAC address will point the frame to the router which will be the first leg of the packet’s journey. If the routers MAC address is not known then an ARP request may be sent.Each host must be told what the IP address of its default gateway is. The ARPtable is stored in the computers RAM with table entries aged out, a timer is set as soon as the request is sent out. This keeps the tables upto date.

IPv6

Class A and B addresses were quickly depleted. The Internet faced running out of IP addresses. IPv6 uses 128 bits rather than the 32 bits currently used in IPv4. IPv6 uses hexadecimal numbers to represent the 128 bits. IPv6 provides 640 sextrillion addresses.

ARP (Address Resolution Protocol)

ARP is more important than RARP or Bootp