Chapter 5: Network and Transport Layers

Loopback

127 address range is reserved for a computer to communicate with itself. Used mostly by developers and system administrators when testing software

TCP Segment

192-bit header (24 bytes) of control information. Contains the source and destination port identifier.

Cisco Internetwork Operating Systems (IOS)

90% of routers use it

Session

A conversation between two computers. When a computer wants to send a message to the receiver, it usually starts by establishing a session with that computer

Open Shortest Path First (OPSF)

A dynamic hybrid interior protocol that is commonly used on the internet. Uses the number of computers and error rates

Intermediate System to Intermediate System (IS-IS)

A link state interior routing protocol that is commonly used in large networks

Routing Protocol

A protocol that is used to exchange information among computers to enable them to build and maintain their routing tables

Dynamic Addressing

A server is designated to supply a network layer address to a computer each time the computer connects to the network

Autonomous System

A simple network operated by one organization. Each system know about the other computers in that system and usually exchange routing information

Quality of Service

A special type of connection-oriented messaging in which different connections are assigned different priorities

Network and Transport Layers

Accept incoming messages from the data link layer and organize them into coherent messages that are passed to the application layer. Transport layer at the sender breaks the message into smaller segments. Network layer at the sender gives the data to the data link layer. Network layer at the receiver receives individual packets, process them, and pass them to the transport layer which reassembles them

Reserved Addresses

Addresses starting from 224 that should not be used on IP networks.

Broadcast Messages

Addresses starting with 255

Centralized Routing

All routing decisions are made by one central computer or router. Commonly used in host-based networks

Subnet Mask

Any portion of the IP address can be designated as a subnet. Every computer in a TCP/IP network is given a subnet mask to enable it to determine which computers are on the same subnet that it is on and which computer are outside its subnet

Internet Corporation for Assigned Names and Numbers (ICANN)

Approves addresses. Responsible for managing the assignment of network layer addresses. Sets the rules by which new domain names are created and IP address numbers are assigned to users. Manages a set of Internet domains and authorizes private companies to become domain name registrars for those domains

Class A

Can have any number between 1 and 126 in the first byte

Dynamic Host Configuration Protocol (DHCP)

Common standard for dynamic addressing. Software package installed on the client that instructs it to contact a DHCP server to obtain an address. Uses leases by picking next available IP address

Link State Dynamic Routing

Computers or routers track the number of hops in the route, the speed of the circuits in each route, and how busy each route is.

Internet Group Management Protocol (IGMP)

Computers wishing to participate in a multicast send a message to the sending computer or some other computer performing routing along the way using a special type of packet

Router Configuration

Console port, network interface port, and auxiliary port

Static Routing

Decentralized, which means that all computers or routers in the network make their own routing decisions following a formal routing protocol.

Subnet

Designed on the network that subdivide the network into logical pieces

Router Functions

Determines a path for a packet to travel. It transmits the packet across the path. It supports communication between a wide variety of devices and protocols

Transmission Control Protocol/Internet Protocol (TCP/IP)

Developed by the U.S Department of Defense's Advanced Research Project Agency network (ARPANET) by Vinton Cerf and Bob Kahn in 1974. Protocol used on the internet. Used by all BNs and WANs, TCP/IP allows reasonably efficient and error-free transmission

Border Gateway Protocol

Dynamic distance vector exterior routing protocol used on the Internet to exchange routing information between autonomous systems. Preferred between Internet sections

Routing Information Protocol (RIP)

Dynamic distance vector interior routing protocol that is commonly used in smaller networks. Broadcast every minute or so

Enhanced Interior Gateway Routing Protocol (EIGRP)

Dynamic hybrid interior protocol developed by Cisco and commonly used inside organizations. Records information

Port Address

Each application layer software package has a unique port address. Any message sent to a computer must tell TCP the application layer port address that is to receive the message. Can be any 16-bit (2 byte) number

Interface

Each connection to the router number from 0 to 3

Data Link Layer Address

Ethernet address. Also called the physical address or the MAC address. It is part of the hardware and can never be changed

Routers

Found at the edge of subnets because they are devices that connect subnets together and enable messages to flow from one subnet to another as the messages move through the network from sender to receiver

Network Layer Address

IP address. www.example.com is translated into an IP address that is 4 bytes long when using IPv4. Determines the best route through the network to the final destination. Assigned by software

Application Layer Address

Internet address/URL (server name). Assigned by a software configuration file.

Three Functions of the Transport Layer

Linking the application layer to the network layer, segmenting, and session management

Transport Layer

Links the application software in the application layer with the network and is responsible for the end-to-end delivery of the message. Accepts outgoing messages from the application layer and segments them for transmission.

Resolving Name Server

Locally stored addresses

Root Servers

Manages where other servers are. Only 13 active in the U.S

TCP/IP

Most commonly used set of transport and network layer protocols.

IP

Network layer protocol and performs addressing and routing. IP software is used at each of the intervening computers through which the message passes. Routes the message to the final destination

Real-Time Transport Protocol

Once RSVP and RTSP establish a connection they use this to send packets across the connection. Contains information about the sending application, a packet sequence number, and a time stamp so the data can be synchronized with other RTP packets by the application layer software

Unicast Message

One computer sends a message to another computer

IP version 4 (IPv4)

One form of IP. Has a 192-bit header (24 bytes). Contains source and destination addresses, packet length, and packet number. Only 4.2 billion addresses (500 million are reserved). Decimals to express addresses

IP version 6 (IPv6)

One form of IP. Has a 320-bit header (40 bytes). Increase in packet size is an increase in address size from 32 bits to 128 bits. Easier to perform routing and supports a variety of new approaches to addressing and routing. 3.4 x 10^38 addresses. Hexadecimal to express addresses

Packets

PDUs at the network layer

Real-Time Streaming Protocol (RTSP)

Permit application layer software to request connections that have certain minimum data transfer capabilities. Geared toward audio/video streaming applications

Resource Reservation Protocol (RSVP)

Permit application layer software to request connections that have certain minimum data transfer capabilities. Geared towards general purpose

Access Control List

Plays an important role in network security

FTP Server

Port 21

Telnet

Port 23

SMTP

Port 25

Web Server

Port address 80

Exterior Routing Protocols

Protocols used between autonomous systems. Designed to be more careful in the information they provide

Name Servers

Provide DNS services. Have address databases that store thousands of Internet addresses and their IP addresses. "Directory"

Multicasting

Ranges 224 to 239 belong to Class D. Sending messages to group of computers rather than one computer

Class E

Ranges 240 to 254 and are reserved for experimental use

Distance Vector Dynamic Routing

Routers count the number of hops (one circuit) along a route

Dynamic Routing (Adaptive Routing)

Routing decisions are made in a decentralized manner by individual computers. Used when there are multiple routers through a network, and it is important to select the best route. Fastest route possible

Interior Routing Protocols

Routing protocols used inside an autonomous system

User Datagram Protocol (UDP)

Second type of transport layer protocol. UDP PDUs are called datagrams. Used when the sender needs to send a single small packet to the receiver (DNS request). Commonly used for control messages such as addressing (DHCP)

Authoritative Server

Server that owns the address. The source of the IP address

NAT Firewalls

Special devices that translate the private addresses on messages that these computers send into valid public addresses for use on the Internet

Top Level Domain (TLD)

Specific designations. Ex. .com, .edu, .org., .net, .gov

Routing Table

Specifies how messages will travel through the network. Two-column table. The first column lists every network or computer that the router knows and the second column lists the interface that connects to it

Three-Way Handshake

Starts with the sender sending a SYN to the receiver. The server responds with an ACK for the sender's/client's SYN and then sends its own SYN. SYN is usually a random generated number that identifies a packet. The last step is when the client sends an ACK for the server's SYN. Once the connection is established, the segments flow between the sender and receiver

Network Layer

Takes the message from the transport layer and routes them through the network by selecting the best path from computer to computer through the network (and adds an IP packet)

Destination port

Tells the TCP software at the destination to which application layer program the application layer packet should be sent.

Source Port

Tells the receiver which application layer program the packet is from

Segment

The Protocol Data Unit (PDU) at the transport layer. The transport layer takes a packet that is split into two smaller TCP segments

Address Resolution Protocol (ARP)

The message is a specially formatted request. "Whoever is IP address xxx.xxx.xxx.xxx, please send me your data link layer address."

Destination Port Address

The port address at the destination computer

Routing

The process of determining the route or path through the network that a message will travel from the sending computer to the receiving computer

Connectionless Messaging

The sender may choose to start a session but just send the one quick message and move on. One short information message or a request. Each packet is treated separately and makes its own way through the network. No connection is established. When desired, the TCP segment is replaced with a User Datagram Protocol (UDP) packet. Commonly used when the application data or message can fit into one single message

Address Resolution

The sender must be able to translate the application layer address of the destination into a network layer address and in turn translate that into a data link layer address

Connection-Oriented Messaging

The sender transmits the segments in sequence until the conversation is done, and then the sender ends the session. Both the sender and receiver must send a SYN (synchronize) and receive a ACK (acknowledgement) segment. Starts with the sender sending a SYN to the receiver. The server responds with an ACK and then sends its own SYN

Internet Control Message Protocol (ICMP)

The simplest interior routing protocol on the Internet. Error-reporting

Server Name Resolution

The translation of application layer addresses into network layer addresses. Done through Domain Name Service (DNS)

Internet Address Classes

Three classes of addresses that can be assigned to organizations: Class A, Class B, and Class C. Assigned by the first byte

Broadcast Message

To send a message to another computer in its subnet, a computer must know the correct data link layer address. Received and processed by all computers in the same LAN

Segmenting

To take one outgoing message from the application layer and break it into a set of smaller segments for transmission through the network. It also means to take the incoming set of smaller segments from the network layer and reassemble them into one message for the application layer

TCP

Transport layer protocol. Links the application layer to the network layer. Performs segmenting: breaking the data into smaller PDUs called segments, numbering them, ensuring each segment is reliably delivered, and putting them in the proper order at the destination. Uses continuous ARQ

Datagram

UDP PDUs. Has only four fields (8 bytes of overhead) plus the application layer packet: source port, destination port, length, and a CRC-16. Does not check for lost messages

Private IPv4 Address Space

Used to increase security and internally by organizations

Multicast Message

Used to send the same message to a group of computers

Classless Addressing

Uses slash to indicate the address range (slash notation)

Source Port Address

When an application layer program generates an outgoing message, it tells the TCP software its own port address

Four-Way Handshake

When terminating a session. Each side of the session has to terminate the connection independently. The sender will start by sending a FIN to inform the receiver that it's finished sending data. The server acknowledges the FIN sending an ACK and sends a FIN to the client. The connection is terminated when the server receives the ACK for its FIN.