Network Technologies

A MAC address is 48 bits long and is represented as a hexadecimal number. Represented in hex, it is 12 characters in length, where each character is 4 bits. To make it easier to read, the MAC address is represented in a dotted hexadecimal format, like this: FFFF. FFFF.FFFF.

Some formats use a colon (:) instead; and in Some cases, the colon separator is spaced after every two hexadecimal digits, like this: FF:FF:FF:FF:FF:FF. the first six digits of a MAC address are associated with the vendor, or maker, of the NIC.

Each vendor has one or more unique sets of six digits. These first six digits are commonly called the organizationally unique identifier (OUI). The last six digits are used to represent the NIC uniquely within the OUI value. In theory, each NIC has a unique MAC address. In reality however, this is probably not true. What is important for your purposes is that each of your NICs has a unique MAC address within the same physical or logical segment.

A logical segment is a virtual LAN (VLAN) and is referred to as a broadcast domain .

Some devices, such as Cisco routers, might allow you to change the MAC address for a NIC, while others won't.

Every data link layer frame has two MAC addresses: a source MAC address of the host creating the frame and a destination MAC address for the device (or devices, in the cast of a broadcast or multicast) intended to receive the frame.

If only one device is to receive the frame, a unicast destination MAC address is used. If all devices need to receive the frame, a destination broadcast address is used.

When all the binary bits are enabled for a MAC address, this is referred to as a local broadcast address: FFFF.FFFF.FFFF.

OSI (Open Systems Interconnect) layers and network components operate:

Hubs Switches, Bridges, Routers, NICs (Network Interface Card), WAPs (Wireless Access Point)

devices at osi layer

Seven layers of the OSI (Open Systems Interconnect) model and their functions.

OSI Layer Model

Network protocols in terms of routing, addressing schemes, interoperability and naming conventions:

TCP/IP

Transmission Control Protocol, A connection based Internet protocol responsible for breaking data into packets, which the IP protocol sends over the network. IP is located at the TCP/IP Internet layer which corresponds to the network layer of the OSI Model. IP is responsible for routing packets by their IP address.

IP is a connectionless protocol. which means, IP does not establish a connection between source and destination before transmitting data, thus packet delivery is not guaranteed by IP. Instead, this must be provided by TCP. TCP is a connection based protocol and, is designed to guarantee delivery by monitoring the connection between source and destination before data is transmitted. TCP places packets in sequential order and requires acknowledgment from the receiving node that they arrived properly before any new data is sent.

TCP/IP model

Application layer
DHCP - DNS - FTP - HTTP - IMAP4 - IRC - NNTP - XMPP - MIME - POP3 - SIP - SMTP - SNMP - SSH - TELNET - BGP - RPC - RTP - RTCP - TLS/SSL - SDP - SOAP - L2TP - PPTP
Transport layer
This layer deals with opening and maintaining connections, ensuring that packets are in fact received. This is where flow-control and connection protocols exist, such as: TCP - UDP - DCCP - SCTP - GTP
Network layer
IP (IPv4 - IPv6) - ARP - RARP - ICMP - IGMP - RSVP - IPSec - IPX/SPX
Data link layer
ATM - DTM - Ethernet - FDDI - Frame Relay - GPRS - PPP
Physical layer
Ethernet physical layer - ISDN - Modems - PLC - RS232 - SONET/SDH - G.709 - Wi-Fi

IPX/SPX

IPX/SPX is the primary protocol of Novell NetWare (in particular, versions 4.0 and earlier, though it can be used on all versions). Internetwork Packet Exchange/Sequenced Packet Exchange developed by Novell and is used primarily on networks that use the Novell NetWare network operating system. The IPX and SPX protocols provide services similar to those offered by IP and TCP. Like IP, IPX is a connectionless network layer protocol. SPX runs on top of IPX at the transport layer and, like TCP, provides connection oriented, guaranteed delivery. IPX/SPX provides many of the same features as TCP/IP, and is a routable transport protocol that allows networks to be segmented. However, network segmentation with IPX/SPX is done with network numbers and not with subnet masks. IPX/SPX is also similar to TCP/IP because IPX/SPX relies on internal protocols for network communication.

IPX

IPX is similar to the operation of UDP of TCP/IP. IPX is a connectionless datagram transfer service. Because it is connectionless, like UDP, it does not require any preliminary connection setup to transmit the data packets. A disadvantage to connectionless communication is that flow control and error correction are not provided during network communication. In addition, packet delivery is not guaranteed. IPX also provides addressing and routing of packets within and between network segments.

SPX

SPX is similar to the operation of TCP of TCP/IP. SPX is connection-oriented data transfer over IPX. Because SPX is connection oriented, flow control and error correction are provided along with packet delivery acknowledgments. SPX allows a single packet to remain unacknowledged at one time. If a packet is unacknowledged, the packet is retransmitted a total of 8 times. If there’s no acknowledgment, SPX considers the connection failed.

SPXII

SPXII is an enhancement to SPX. SPXII has several improvements over SPX. SPXII allows more than one packet to remain unacknowledged. SPXII also allows for a larger packet size, which improves network performance by reducing the number of acknowledgment packets placed on the network.

NetBEUI

NetBIOS Enhanced User Interface was designed as a small, efficient protocol for use in department-sized LANs of 20-200 computers that do not need to be routed to other subnets. NetBEUI is used almost exclusively on small, non-routed networks. A LAN-only (non-routable) protocol used in early Windows networks based on the NetBIOS API, NetBEUI is a Windows protocol that even Microsoft doesn't recommend for any but the most isolated networks. NetBEUI isn't required for NetBIOS functionality. As an extension of NetBIOS, NetBEUI is not routable, therefore networks supporting NetBEUI must be connected with bridges, rather than routers, like NetBIOS, the NetBEUI interface must be adapted to routable protocols like TCP/IP for communication over WANs.

AppleTalk

The AppleTalk routing protocol is, amazing as it may sound, used by Macintosh networks. There are two important factors to understand about the AppleTalk protocol: zones and network numbers. AppleTalk network numbers assign AppleTalk networks unique numerical values that identify them as segments. Clients and servers can be part of only one network number. Because AppleTalk is routable, clients can access servers from any network number. AppleTalk also uses zones to aid clients in browsing an AppleTalk network. Zones allow servers, printers, and clients to be grouped logically for the purpose of resource access. Unlike network numbers, servers, printers, and clients can be part of more than one zone. Having membership in more than one zone allows clients easier access to network resources. Clients need not use the Chooser to view the resources of multiple zones.