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Network+ TechNotes - Mac OS X Networking

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MAC OS X Networking

Mac OS X is Apple’s current operating system for Macintosh computers. It is a UNIX-like system, which in contrary to its early predecessors is able to communicate with other systems such as Netware, UNIX, Linux, and Windows servers, through TCP/IP. Macintosh computers are particularly popular in the graphical and publishing industry, but also in other industries you are more than likely to find a couple of Macs attached to the network.

AppleShare IP is Apple’s former server software and includes a print, mail and web server. AppleShare can serve Mac AppleTalk, IP, and Windows clients through TCP/IP, AFP, SMB/CIFS, and other protocols and services. AppleShare has been replaced with Mac OS X Server, which is a UNIX/BSD based system and supports communication with UNIX, Linux, Mac, and Windows clients, and servers, through the former mentioned protocols, including those mentioned in the UNIX/Linux Networking TechNotes. Mac OS X uses an access permission system based on a UNIX. Every file and folder on a hard disk has an associated set of permissions that determines who can read, write, and/or execute.

Apple not only conformed to the Internet Protocol (IP), but also introduced several other features in Mac OS, such Open Directory and Bonjour, which makes setting up a network a simple job even for users. Open Directory is Apple’s answer to Microsoft’s Active Directory and Novell’s eDirectory. It is an Open LDAP-based directory and supports Kerberos authentication. In addition to allowing better integration and management of Mac OS X and Mac OS X Server systems, it also supports Linux and Windows systems and can be connected to the former mentioned directories.

Bonjour, formerly named Rendezvous, essentially allows you to create a plug-and-play network, also known as zero-configuration networking . Different type of network devices, such as Windows and Mac computers, network printers, and mobile devices such as PDAs, can automatically interoperate in a network without requiring the user to configure anything. Network devices can assign themselves an IP address from the 169.254.x.x range using called link-local addressing (Microsoft Windows systems use the same range for APIPA) when a DHCP server is not available. Bonjour uses a special type of DNS called Multicast DNS–Service Discovery (mDNS-SD) to implement a naming system that doesn’t require a dedicated DNS server in the network. Instead, network devices broadcast their name, which is then stored locally on the other network devices in the network, like a hosts file, but dynamic. Services such as file and printer shares are also automatically discovered. Bonjour is available as a free download for Windows computers.

AppleTalk

AppleTalk was developed by Apple in the early 1980s to allow file and printer sharing and mail functionality between Macintosh computers. Like TCP/IP, AppleTalk is not just a single protocol, but a suite of several protocols and services for different purposes. It is built-in in every Macintosh computer, requires virtually no user interaction, and is therefore very easy to administer in small network environments. Although most modern Macintosh computers are now configured solely with TCP/IP, AppleTalk can still be found in corporate networks and is still listed in the exam objectives of the N10-004 Network+ exams. As with any network protocol, AppleTalk is best explained in correlation to the 7-layer OSI model.

AppleTalk includes media specifications at the Physical and Data Link layers that allow AppleTalk to run over network types with different media-access technologies. EtherTalk allows AppleTalk to run over Ethernet, TokenTalk allows AppleTalk to run over Token Ring, FDDITalk allows AppleTalk to run over FDDI, and LocalTalk is Apple's own media-access technology. LocalTalk uses the CSMA/CA access-method, UTP or STP cabling, and has a maximum data transfer rate of 230 Kbps. There may be some small networks left in which it is used for simple file and printer sharing. Later versions of AppleShare include AppleTalk over IP, which allows AppleTalk traffic to be encapsulated in IP packets, creating a tunnel through which AppleTalk clients and servers can communicate and advertise services.

The image below shows a connector used in LocalTalk networks to connect network nodes. At one side, it connects to a computer or printer using a mini-din or DB-9 serial connector. The other side connects to a phone cable, which in turn, connects to another LocalTalk connector or a terminator. This type of media is known a PhoneNet, and is similar to building a 10Base2 bus network topology.



At the Network layer, AppleTalk defines two main protocols:

Datagram Delivery Protocol (DDP)

A connectionless datagram protocol that provides best-effort delivery and layer 3 addressing. It is very similar to the function of IP.

AppleTalk Address Resolution Protocol (AARP)

Maps (Network) layer 3 addresses to (Data Link) layer 2 MAC addresses. This is Apple’s version of the ARP protocol used in TCP/IP.

At the Transport layer, a big difference with the TCP/IP suite becomes noticeable. In TCP/IP, the routing protocols are defined at the Network layer, while AppleTalk defines them at the Transport layer:

Routing Table Maintenance Protocol (RTMP)

Allows AppleTalk routers to exchange information and build their routing tables. RTMP routers broadcast their routing table to neighboring routers every 10 seconds causing a lot of overhead. RTMP is the equivalent of the Routing Information Protocol (RIP) used in TCP/IP networks.

AppleTalk Update-based Routing Protocol (AURP)

Allows AppleTalk networks to be connected over a TCP/IP WAN link. AURP wraps AppleTalk datagrams into UDP datagrams allowing them to be tunneled over IP connections.

AppleTalk Echo Protocol (AEP)

Used to verify whether remote hosts are reachable. This is similar to ICMPs Echo messages used by the PING utility in TCP/IP networks.

AppleTalk Transaction Protocol (ATP)

This is the transport protocol in AppleTalk and provides reliable delivery service for transactions. ATP handles acknowledgements, flow control and sequencing.

Network Binding Protocol (NBP)

Maps AppleTalk names to AppleTalk network layer addresses. This protocol is largely responsible for the large overhead on AppleTalk networks because of the broadcast method it uses. NBP is somewhat similar to DNS and WINS in TCP/IP.

At the Session layer, AppleTalk defines the Printer Access Protocol (PAP), which manages the virtual connection between client and printers and print servers. The AppleTalk Data Stream Protocol (ADSP) and the AppleTalk Session Protocol (ASP) to establish and manage session with remote hosts. And the Zone Information Protocol (ZIP), which manages the relationship between network numbers and zone names and allows applications to use zones.

At the Presentation and Application layer, the AppleTalk Filing Protocol (AFP) is defined. AFP allows a workstation on an AppleTalk network to access files on an AFP file server, such as an AppleShare file server, or NAS device. When the user opens a session with an AppleShare file server over the network, it appears as if the files were located on a local disk drive.

AppleTalk Addressing

The following network diagram shows an example of a simple AppleTalk network using EtherTalk:



An AppleTalk network consists of three main components:

Nodes

Uniquely identified hosts on the network. Examples are Macintosh workstations, printers, Windows PCs, and routers.

Networks

Multiple network numbers can be assigned to a single segment, known as an extended cable range.

Zones

Similar to the concept of VLANs, they are used to control broadcast traffic by dividing internetworks into logical groups. When a client request resources such as shares and printers, only those in the same zone of the client, will appear by default.

An AppleTalk address is 24 bits in length and as with all routable protocols, has a network and a host portion. The first 16 bits denote the network portion of the address, and is automatically learned from another AppleTalk computer or a router. The remaining 8 bits denote the node portion. When a client is added to the network, it will make up the node portion itself and broadcast messages to see if the number is already in use. If the number is in use, the client will generate a new number and start over again until an unused node number is found. The 16 bits network portion allows for 65000 networks and the 8 bits node portion allows for 254 hosts (0 can't be used, 255 is the broadcast address). AppleTalk phase 2 allows multiple network numbers to be assigned to a single segment, known as an extended cable range, and eliminates the limit of 254 nodes per network.

The complete AppleTalk network address of node 37 in the above diagram is 58.37. Sometimes the address includes a socket number, for example 58.37.254 or 58.37/254. An AppleTalk socket is similar to the concept of ports in TCP/IP. Using the Network Binding Protocol's services, AppleTalk objects can be named. AppleTalk names consist of an object, type and zone field, where each of these three parts are limited to 32 characters in length. An example of a printer name could be Finance1:LaserWriter@Executive, where Finance1 is the name configured for the object, LaserWriter the object type, and Executive the zone name.


 

Current related exam objectives for the Network+ exam:

2.4 Differentiate between the following network protocols in terms of routing, addressing schemes, interoperability and naming conventions:
- AppleTalk / AppleTalk over IP (Internet Protocol)

2.13 Identify the purpose of network services and protocols (For example: AFP (Apple File Protocol).

3.1 Identify the basic capabilities (For example: client support, interoperability, authentication, file and print services, application support and security) of the following server operating systems to access network resources:
- UNIX/Linux/Mac OS X Server
- AppleShare IP

3.2 Identify the basic capabilities needed for client workstations to connect to and use network resources (For example: media, network protocols and peer and server services).

3.4 Given a remote connectivity scenario comprised of a protocol, an authentication scheme, and physical connectivity, configure the connection. Includes connection to the following servers:
- UNIX / Linux / MAC OS X Server
- AppleShare IP

4.5 Given a troubleshooting scenario between a client and the following server environments, identify the cause of a stated problem:
- UNIX / Linux / Mac OS X Server
- AppleShare IP



Click here for the complete list of exam objectives.

Discuss this TechNote here Author: Johan Hiemstra




 

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