Data link addresses are physical addresses most often referred to as the MAC address (Media Access Control). MAC addresses are explored further in the next objective.

Network addresses exist at the Network layer and are logical (versus physical) addresses.

MAC addresses are uniquely assigned to devices and there are no duplicates. They are hexadecimal addresses (12 digits) that are separated by dashes. The first six digits identify the manufacturer, and the last six identify the device.

The primary function of MAC addresses is to uniquely identify the network interface card (NIC) or other device. In TCP/IP, ARP (Address Resolution Protocol) is used to map the IP address (logical) to the MAC address (physical).

An example of a MAC address is: 00-03-47-3c-1c-25

1. Changes in one area do not affect other areas.
2. Dividing the tasks makes each element less complex.
3. Vendors can implement solutions at one or more layers without having to recreate the entire model.

The two parts of the network address are the network id and the host id. The division between the two, in TCP/IP, is obtained by comparing/contrasting the subnet mask against the IP address. You must know the three classes of host addresses (A, B, and C), and how to subnet, as detailed at: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ip.htm

1. Upper layers convert the message to data and send it to the Transport layer.
2. The Transport layer converts the data to segments and sends it down to the Network layer.
3. The Network layer converts the segments to packets and sends them to the Data Link layer.
4. The Data Link layer converts the packets to frames and sends them to the Physical layer.
5. The Physical layer converts the frames to 1's and 0's (electrical signals) and sends them across the network.

At each layer, header information is added. At the receiving end, the process is reversed, with headers being stripped off at each layer.

As the name implies, connection-oriented services must have a connection in order to communicate. A classic example of this is FTP, used to transfer files from one host to another. A connection must exist between the two hosts before communication can commence.

Connection-less protocols communicate without a dedicated connection existing. The classic example of this is e-mail -- when you send a message, it may reach the host it is intended for immediately or quite a while later. You send the e-mail without a dedicated connection.

In the world of TCP/IP, TCP is the Transport layer protocol that is used when a connection is required; while UDP is used in its place with a connection is not required. A primer from Cisco on understanding TCP/IP can be found here.

This is basically commonsense and overlaps with earlier objectives. An IP address has two parts, and so on. You should review NetWare Protocols as posted here.

LAN segmentation reduces the number of nodes per segment and makes administration easier, reduce bandwidth waste, and improve scalability.

The key issue is that the bridge relies upon the MAC address to determine whether the host to be reached is on this network segment or not. If the host is on this segment, then the data is left alone to travel throughout the network (and reach the host). If the host is not on this segment, then the data is sent across the bridge. Bridges can be used to connect two segments together, and no more than two.

An O.K. overview from Cisco can be found within this document.

The router allows more than one segment to be communicated with. Instead of relying on MAC (layer 2) addresses, the router uses Network (layer 3) addresses. Click here for more information.

Switches move the discussion into the VLAN realm and offer performance increases over other solutions due to physical definitions as opposed to logical, etc. The best overview for this topic can be found here.

Click here.

Click here.

Click here.

There are five classes of IP addresses, distinguishable by the first digits (octet):

Class A - 0 to 126
Class B - 128 to 191
Class C - 192 to 223
Class D - 224 to 239
Class E - 240 to 255

Classes A, B, and C are used for assigning numbers to hosts, while Class D is generally used for Multicasting, and Class E is used for experimentation and broadcasting. The 127 octet range is reserved and cannot be used, as 127.0.0.1 is the loopback address for each host.

Using all of the numbers within the range, it is possible to have 16 million hosts on a Class A network, 65,000 on a Class B network, and 254 on a Class C network. Subnetting allows you to divide the network into a number of smaller networks, and reduces the number of hosts that can exist (overall and on each subnet).

The Cisco overview available here contains the necessary exam information on addresses and subnets.

The Network layer is where IP addressing and routing take place. Not only does IP operate at this layer, but ICMP (Internet Control Message Protocol) does as well. Think: addressing, routing, and basic communication. Click here for more information.

IP addresses can be configured in one of two ways: manually or automatically. To configure addresses manually, you go to the host and enter an address that is unique within the scope of that host's communication range. This means that if the host is directly connected to the Internet, the address given to it must be unique within the entire Internet. On the other hand, if the host communicates only with a handful of other hosts, and reaches the Internet through a NAT (Network Address Translation) server, then the address need only be unique among the hosts it communicates directly with. Each operating system has a slightly different utility for entering the addressing information, but global among them all is the fact that you must not only enter the address for the host, but also related information. Related information includes the subnet mask, and can include such variables as the default gateway (router), DNS server, WINS server, etc.

To automatically configure hosts, you must set up a DHCP (Dynamic Host Configuration Protocol) server on your network and give it a pool (scope) of addresses that it can issue to hosts. The hosts contact the DHCP server and it leases them an address (and associated variables) from the pool for a set time period. If the information is no longer needed, it will be returned to the pool, but as long as it is needed, the host will continuously try to renew the lease from the server.

DHCP simplifies administration and management of IP addressing.

There are a number of tools that can be used to verify IP addresses. To see the values that have been assigned to a host, you can use the ipconfig utility with Windows NT and Windows 2000, or the winipcfg utility with Windows 9x. Similar functionality is present with the ifconfig utility in Unix and Linux.

You can test the address by pinging it from and seeing the response. Similarly, name resolution can be verified by pinging the host with the host name rather than the IP address.

The other primary utility you can use is trace (tracert/traceroute/etc. - dependent upon the operating system). This utility works like ping except not only does it show you that a response is received, but it will also show the hops taken to receive that response.

An IPX address, like an IP address, consists of two parts - network and host (node). 32 its of the address identify the network, while 48 bits identify the host for a total address of 80 bits.

IPX encapsulation occurs at the Data Link Layer and four types can be used over Ethernet:

1. Ethernet_II
2. Ethernet_802.2
3. Ethernet_802.3
4. Ethernet_SNAP (SubNetwork Access Protocol)

A description of the four types can be found here.

You can see the IPX address with the command:

Show IPX interface {interface}

Where {interface} is replaced by the name of the interface - such as "ethernet 0". Other commands that would be useful include:

Show ipx route

And

Show ipx traffic

For a list of IPX commands, click here.

To add RIP (Routing Information Protocol) to your configuration, the primary command is:

router rip

A list of all the commands employed can be found here.

The primary way IGRP differs from RIP is in that each router with IGRP can have multiple default routes. To add IGRP (Interior Gateway Routing Protocol) to your configuration, the primary command is:

router igrp

Click here for more information.