Lesson 3 Understanding the OSI Model

ipconfig

A command-line tool that can display TCP/IP configuration information for a system. It can also change some of the configuration settings

Transmission Control Protocol (TCP)

A connection-oriented protocol that provides guaranteed delivery. TCP uses a three-way handshake session, uses sequence numbers to track packets, and includes regular acknowledgements. The alternative is UDP, which is a connectionless protocol that provides best-effort delivery

User Datagram Protocol (UDP)

A connectionless protocol that provides a best-effort delivery. The alternative is TCP, which is a connection-oriented protocol that provides guaranteed delivery

Internet Message Access Protocol (IMAP)

A mail protocol used to store email messages and download them to clients when requested. Users can view email message headers and choose whether to download the email messages or not. This differs from POP servers which download the messages as soon as the client connects. Clients use SMTP to send email. IMAP4 uses port 143

Simple Network Management Protocol (SNMP)

A management protocol used to query and manage network devices such as routers and switches. SNMP uses ports 161 and 162

Simple Mail Transfer Protocol (SMTP)

A primary protocol used to send email on the Internet and internal networks. Clients use SMTP to send email to email servers. Email servers use SMTP to send and recieve email between other email servers. SMTP uses port 25

Internet Control Message Protocol (ICMP)

A protocol used to carry error messages and messages about the availability of services. Troubleshooting tools such as Ping, PathPing, and tracert us ICMP. ICMP uses IP directly and doesn't use either TCP or UDP

Internet Group Management Protocol (IGMP)

A protocol used to multicast data to a group of computers. This is in contrast to unicast, which sends data from one computer to one computer, and broadcast, which sends data from one computer to all other computers in a subnet.

Lightweight Directory Access Protocol (LDAP)

A protocol used to query directories such as Microsoft's Active Directory Domain Services. LADP uses port 389. LADP can be secured with either SSL or TLS. Secure LADP uses port 636

File Transfer Protocol (FTP)

A protocol used to transfer files over the Internet using TCP. MAny operating systems such as Windows 7 include an FTP command-line tool. FTP uses ports 20 and 21

Open Shortest Path First (OSPF)

A routing protocol added to a router. Routing protocols allow routers to exchange routing information between each other. OSPF is used in place of RIPv2 on many hardware routers

Routing Information Protocol

A routing protocol added to a router. Routing protocols allow routers to exchange routing information between each other. RIPv2 is the current version and has replaced RIPv1 in most applications.

Trivial File Transfer Protocol (TFTP)

A scaled down version of File Transfer Protocol (FTP). TFTP uses UDP as the transport protocol and can't be used on the Internet

TCP/IP

A suite of protocols used on the Internet and Microsoft networks. It includes TCP, IP, and many other protocols

Layer 2 Tunneling Protocol (L2TP)

A tunneling protocol used for VPNs. L2TP is commonly used with IPSec (as L2TP/IPsec) when used in a VPN. L2TP uses port 1723

Layer 3 Switch

An advanced switch that can operate on layer 3 similar to a router. Layer 3 switches function just like a router but perform routing using internal hardware instead of software.

Post Office Protocol version 3 (POP3)

An email protocol used to download email to clients as soon as the client connects to the email server. Clients use SMTP to send email. POP3 uses port 110.

Internet Protocol Security (IPSec)

An encryption protocol that includes an Authentication Header (AH) for authentication and Encapsulating Security Payload (ESP) for encryption. IPSec is used with L2TP/IPSec for VPNs

Internet Protocol (IP)

IP is a logical addressing scheme used with networking. IPv4 has been around since the 1980s and IPv6 is the newer version. Both are currently being used on the Internet and in internal networks. Eventually IPv6 will replace IPv4

Link Aggregation Control Protocol (LACP)

LACP is defined by IEEE 802.3ax and is responsible for allowing bundled links on switches to linked devices. Bundled links allows higher throughput between devices

Physical Layer

Layer 1 of the OSI Model. Hubs and repeaters are examples of devices at this layer. Ethernet and Token Rink are examples of protocols on this layer.

Data Link Layer

Layer 2 of the OSI Model. It has two sublayers: Logical Link Control (LLC) and Media Access Control (MAC)

Network Layer

Layer 3 of the OSI Model. It maps to the Internet layer of the TCP/IP Model. The network layer of the OSI is responsible for routing and selecting the best path to another network. Routers and layer 3 swithches operate on this layer. IPv4, IPv6, ARP, and ICMP operate on this layer

Transport Layer

Layer 4 of the OSI Model and one of the layers of the TCP/IP Model. The Transport layer is responsible for flow control, reliability, and error checking. TCP and UDP protocols operate here.

Session Layer

Layer 5 of the OSI model. The Session layer establishes, maintains, and terminates the session between two devices.

Presentation Layer

Layer 6 of the OSI Model. It is responsible for translation between different formats, encryption, decryption, compression, and decompression

Application Layer

Layer 7 of the OSI Model and the top layer of the TCP/IP Model. Protocols such as DNS, DHCP, and SMTP operate on the Application layer. Proxy servers and advanced firewalls operate on the Application layer

Segment

On the physical network, a segment is a common connection between multiple computers. On the OSI model, a segment is the name of data traveling on the Transport layer. Packets travel on the Network layer and frames travel on the Data Link layer.

Internet Layer

One of the layers on the TCP/IP Model that maps to the Network layer of the OSI Model. Routers operate on this layer

MAC address

The MAC address is a 48-bit hardware address that is required by every device on a LAN to communicate on that segment. The switch uses the MAC address in the MAC table.

Open Systems Interconnect (OSI) Model

The Open Systems Interconnect (OSI) model is a framework for network communication. It includes seven layers: Application, Presentation, Session, Transport, Network, Data Link, and Physical.

TCP/IP Model

The TCP/IP Model describes a virtual networking model that was created bu the U.S. Department of Defense in the 1970s. It includes four layers known as Application, Transport, Internet, and Link

Link Layer

The lowest layer of the TCP/IP Model. It maps to the Data Link and Physical layers of the OSI Model

Hypertext Transfer Protocol (HTTP)

The primary protocol used to transfer web pages and web elements such as pictures and audio files over the Internet. HTTP commonly transfers HTML files that are displayed in web browsers. HTTP uses port 80. HTTPS is a secure version of HTTP using port 443