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Old Macintosh Networking Primer

This document describes some of the principles in configuring older Macintoshes running System 6 through System 9.x to access the internet. Two sections cover network hardware (ethernet cards, routers, modems) and the TCP/IP network protocol.

This document is designed to be read in conjunction with two other guides.

Old Macintosh System Software and TCP/IP describes what software you need to install to use TCP/IP on a Mac. The guide covers System 6 through to Mac OS 9.x. It includes specific information on configuring MacTCP.

Sharing Your Internet Connection with an Older Mac describes how you might access the internet using your existing dial-up or broadband connection.

Other useful sites that describe basic Mac networking include:

Three Macs and a Printer (

AppleTalk-ing at the Mac 512UG (

the pickle's Low-End Mac FAQ (

Network Hardware Primer

This document concentrates on ethernet networking. Information on internet networking using LocalTalk will added in the future.

Ethernet Adapter or NIC

A Network Interface Card (NIC) is the hardware that connects a computer to a network. Ethernet is the most common standard for networks but NICs are available for other types of network (eg LocalTalk or Token Ring).

Ethernet NICs have been produced for almost every Macs that does not have ethernet built-in. You may find new old stock at Mac clearance specialists but second hand is usually cheaper. Some compact Macs (Plus, Classic) and early Powerbooks can't accept a traditional NIC so you will have to locate an ethernet interface that plugs into the Mac SCSI port.

Another option for such Macs is a LocalTalk to ethernet adapter that plugs directly into the Mac serial port but these are slower than real ethernet. These devices are readily available second hand but make sure that you get the right model for your requirements. Farallon and Asante are the best known manufacturers. The Asante Talk and AsantePrint devices are designed for AppleTalk only; the Farallon EtherWave and EtherMac adapters support AppleTalk and MacTCP but the degree of support for Open Transport is unclear. Some devices are designed for use with printers only; other work with printers and Macs.

The earliest compact Macs (128, 512k 512ke) do not have SCSI interfaces and cannot use an external SCSI port ethernet interface. The earliest compact Mac with SCSI is the Mac Plus. Older compact Macs fitted with a RAM upgrade, SCSI port and 128KB ROM upgrade are functionally equivalent to a Mac Plus.

Use the utility GURU to see whether your older Mac has built-in ethernet capability and to see which expansion slot (PCI, NuBus, CommSlot, PCMCIA, PC Card) options are available.

Many older Mac ethernet cards do not have any clear labels or silk screening. This is applicable to cards from Apple and third party manufacturers. You can use an application such as TattleTech in a Mac running System 7.0 --> 9.x to help identify unknown cards.

For information on drivers for Macintosh ethernet cards, refer to the document Macintosh System Software and TCP/IP.

Ethernet Cabling and Speeds

Most modern networks now use utp (unshielded twisted pair) ethernet cabling but older networks may have used coaxial thinwire cabling. utp uses RJ45 jack connectors and thinwire uses BNC connectors.

RJ45 and RJ11

The blue cable has an RJ45 jack connector for utp ethernet.

The grey cable has an RJ11 jack connector which is used for US telephones and for Apple PhoneNet networking.

Thinwire and AUI connectors

The connector on the left is coaxial BNC for thinwire networking.

The connector on the right is AUI for use with an additional transceiver.

Thwire broken out

From left to right: standard thinwire terminator, T-connector and cable.

Thinwire T-connector assembled

Fully assembled thinwire T-connector and terminator.

Typical utp networks usually operate at 10Mbps or100Mbps (note that Mbps stands for Megabits per second, not MegaBytes); thinwire networks operate only at 10Mbps. Gigabit utp networks operate at 1000Mbps and may not be compatible with older Mac or PC utp ethernet cards.

If your older Mac NIC has a BNC network connector, it can be connected to a utp network using a hub that has both RJ45 and BNC connectors. Refer to the notes on How to Connect Thinwire Ethernet below.

If an older NIC has more than one connector, it will need to be configured to use the right one. Some NICs use an external switch, others use jumpers. The labelling can be confusing -- some common abbreviations used on jumper labels are:

TP -- unshielded twisted pair
THIN -- thinwire
BNC -- thinwire
TW -- thinwire

Some Useful Terms Defined


An AUI connector uses an additional transceiver to connect an ethernet device to a utp or thinwire network. AUI connectors are commonly found on older network hubs and on older Mac/PC/Unix workstation ethernet adapters. The AUI connector may also be called DIX.

An AUI connector is similar to a Mac 15 pin monitor connector; a very clear difference is that the AUI connector uses a spring bayonet fitting to secure a transceiver rather than thumb screws. If you connect a monitor to an AUI connector you will probably damage both.


AAUI is Apple's implementation of AUI; the connector is much smaller than AUI in order to fit in the limited space on the back of a Mac. Special AAUI transceivers are required but these are relatively easy and cheap to obtain second hand.


ISDN was the fastest connection available to domestic users over copper telephone cables before the introduction of DSL/ADSL and cable modem services. ISDN is still the fastest option for many people living in rural areas. NuBus and PCI ISDN cards are available for Macs.

Broadband Connection

Broadband generally refers to anything faster than dial-up or ISDN. Broadband connections are "always on", allowing you to connect to the internet without waiting for a dial-up connection to be established. The down side is that your network becomes more attractive to hackers.

Ethernet (MAC) Address

Every ethernet device has a unique MAC (Media Access Controller) address. This is a twelve digit hexadecimal number such as 00:03:93:16:f2:ce. On many corporate networks, the MAC address is used by a DHCP server to allocate a computer's IP address and configuration.

Routers and Bridges

A bridge is an unintelligent device that joins two networks. All traffic from one network is passed to the other network. A router is more selective and only directs traffic from one network if it is targetted at a computer on the second network. Cable modem or DSL/ADSL devices (not USB modems) that are designed to be shared by several computers function as routers -- they route TCP/IP network traffic from your network to your ISP's network (the internet).

Switches and Hubs

A hub links together network cables from several computers or networks. With utp ethernet, a hub functions as a bridge and data generated by any device connected to the hub is visible to all other devices. A switch is an intelligent hub that only passes data along a utp cable if it is addressed to the connected computer.

Cross Over utp Cable

A cross over utp cable is often used to connect two computers together without the need for a hub or switch for simple file transfers. Some ethernet NICs that switch between 10Mbps and 100Mbps automatically (autosensing) are unable to work with a cross over cable; in such cases, replace the cross over cable with two standard utp cables and a basic hub. A cross over cable is sometimes used for linking two hubs together.

Many older ethernet NICs do not work correctly with cross over cables so it is best to use a proper hub or switch whenever possible. Always label cross over cables carefully.

USB Cable or DSL/ADSL Modem

These devices are intended for connecting a single Mac or PC to a cable or DSL/ADSL connection. You can only use one of these with a modern Mac running Mac OS 8.5 or higher or with a modern PC (Windows 98 is generally the lowest supported operating system).

If you use a USB device, you can still share your internet connection using software on your PC or Mac.

Combined ADSL/Cable Modem and Ethernet Hub

The combined modem/ethernet hub is the easiest way to share a broadband connection between several computers. You should look for one that includes a modem suitable for your broadband connection type, an ethernet hub or switch, wireless networking (optional) plus built-in DHCP, DNS proxy and NAT servers and firewall.

Whilst combined devices are handy for building small networks they need to be treated with caution when adding them to an existing network. If your existing network includes DHCP, DNS proxy and NAT servers, make sure that you disable duplicated services on your combined device.

Apple Airport and Wireless Networking

Airport and Airport Extreme are Apple's names for wireless networking that uses the 802.11b and 802.11g international standards. Some Airport products provide functionality that is not available in products from other vendors, in which case they may be a better choice for a network of several modern Macs. Other Apple products are no better than cheaper ones from other manufacturers. Wireless networking is notorious for incompatibilities between products from different manufacturers so always buy products that can easily be returned if they don't work.

Most wireless networking products are designed for TCP/IP networking, not AppleTalk. If you need Appletalk networking to support older Macs, check the product specification carefully before buying.

How to Connect Thinwire Ethernet

The most basic thinwire network only requires two computers with suitable ethernet cards, a length of thinwire cable, two BNC T-connectors and two thinwire terminators. To create a mini network that is functionally equivalent to using a cross over utp cable:

  1. Screw a terminator onto one side of each T-connector.
  2. Connect your cable to the other end of each T connector.
  3. Connect a T-connector directly to the BNC connectors on your two computer ethernet cards.

To connect a single computer with a BNC network connector to a utp network, you need a hub that has both RJ45 and BNC connectors, a length of thinwire cable, two BNC T-connectors and two thinwire terminators.

  1. Follow the supplier's instructions to join the second hub to your existing utp ethernet network.
  2. Screw a terminator onto one side of each T-connector.
  3. Connect your cable to the other end of each T connector.
  4. Connect one T-connector directly to the BNC connector on your computer ethernet card.
  5. Connect the second T-connector directly to the BNC connector on your hub.

To add another computer to your thinwire network, you need a new length of thinwire cable and another T-connector.

  1. Unscrew the terminator from the T-connector at one end of your network.
  2. Connect your new cable to the free end of the T connector.
  3. Connect your new T-connector at the other end of the cable.
  4. Screw the terminator onto the new T-connector.
  5. Connect the new T-connector directly to the BNC connector on your new computer.

Never connect thinwire into a loop.

Ensure that there is a terminator at each end of the thinwire network.

Never connect a cable directly to the BNC connector on an ethernet card. Always use a T-connector.

Apple Thinwire Transceivers

The Apple Ethernet Thin Coax Transceiver behaves slightly different to conventional thinwire devices. The transceiver can only be used with a Mac or Apple device (eg printer) with an AAUI ethernet connector. It does not need a normal thinwire T-connector and, when used with the special Apple Ethernet Self-Terminating Cable, a conventional terminator is not required. The image below is taken from the Apple Ethernet Thin Coax Transceiver user guide.

In practice, it is best to use a conventional thinwire cable (which is much easier to obtain) and a conventional termnator with the Apple Ethernet Thin Coax Transceiver. When connecting the transceiver to a thinwire network, use the BNC connectors on the transceiver in the same way as the BNC connectors on a T-connector.

Never connect a T-connector to the BNC connectors on an Apple Ethernet Thin Coax Transceiver.

TCP/IP Primer

TCP/IP is the network protocol used on the internet. It has become the dominant protocol for computer networking but older networks may still use protocols such as IPX (for Novell Netware servers) or AppleTalk (for AppleShare servers).

IP Address

The IP address uniquely identifies a computer or other device on a TCP/IP network. Addresses are classified as Public where they are to be used on the internet and Private for use on networks that are not connected to the internet. As the internet has grown, public IP addresses have become a scarce resource. A work around to this shortage is to use a NAT (Network Address Translation) server that allows a network of computers using private addresses to connect to the internet.

Traditionally ISPs have supplied their customers with a single IP address from the public address range; as public addresses have become scarcer, ISPs have started to supply private ISP addresses and provide a NAT at the ISP to connect you to the rest of the world. Either type of IP address/connection from your ISP can be shared with other computers on your local network.

Private IP Address Ranges

Three IP address ranges have been explicitly reserved for use on private networks and are defined in the standards document RFC 1597: "Address Allocation for private Internets". The ranges are: -> -> ->

You can use these addresses freely on your local network. However, if your ISP has issued a private IP address to you, do not use the same address range for your own network. For example, if your ISP has issued you, do not use any addresses in the range -> because they may already be used by other customers of your ISP.


Dynamic Host Configuration Protocol is used to allocate IP addresses automatically. A DHCP server can be configured to allocate an address to any computer that asks for one or it can allocate addresses only to specific MAC addresses. It can also allocate addresses from a pool (so the computer has a different IP address each time it is used) or it can allocate a specific IP address to a specific MAC address.

If you have a number of network black boxes on your network, make sure that only one is configured as a DHCP server.

DHCP is a popular option because it can be set up to be "plug and go" when working with modern computers. Older computers may not work with DHCP, hence the reluctance of many ISPs to support old Macs. With a bit of fiddling, you can usually configure your old Macs to work by giving them fixed private IP addresses.

DNS Servers

Domain Name System servers convert friendly computer names (eg to less friendly IP addresses (eg Your ISP will run two or more DNS servers and there is rarely any need to run your own on a small network. DNS server addresses are usually configured by DHCP for modern computers but you may have to set them manually for older Macs.

If you connect to the internet via an intelligent ADSL/cable modem, it may incorporate a DNS Proxy. You can configure computers on your network to use the local DNS proxy or use the DNS servers at your ISP. Use the proxy if your ISP's DNS servers are slow.


Network Address Translation servers allow you to connect computers on a private IP network to the public internet. This is not usually possible because private IP addresses are not routed on the internet. A NAT server must run on a computer or device that can communicate with the internet. NAT software is often called "internet connection sharing".

NAT works by modifying IP packets originating on the private network to appear as if they originated from the NAT server (which has a route to the internet). NAT also peforms the reverse operation to direct packets originating from the internet to the appropriate destination on the private network.

Some ISPs do not provide public IP addresses to their customers and allocate private IP addresses that are managed using NAT. NAT is a virtually invisible process and you will still be able to share a connection to your ISP that runs over a private IP address.

Some applications, including VPN (Virtual Private Network) software and games do not work well or at all with NAT. There are no problems with popular applications such as web browsers, email or telnet. Some applications such as Ircle provide specific support for Macs running behind a NAT server.

Fixed IP Addresses

Most ISPs will provide you with a public IP address that changes every time that you connect to the internet. This is inconvenient if you need to run any sort of server as those computers connecting to the server will need to obtain its new address first; there are public internet servers that provide this service if you need it (eg

A fixed public IP address remains constant and is more convenient to use if you are running servers. Fixed IP addresses are a scarce resource so your ISP may not provide them or may make a charge.

Hardware and Software Firewalls

A firewall is a system or program that is designed to prevent unauthorised access to a computer from the internet.

Google's Detailed Definition of a Firewall

Web Proxy Server

Most ISPs provide a proxy server which contains cached copies of web pages; web browsers can be configured to use a specific proxy server. Use of a proxy server helps reduce bandwidth consumption by the ISP and some ISPs force all HTTP requests through their proxy servers.

Proxy servers can also be used in place of a NAT to private internet services to computers on a local network. The disadvantages are that proxy servers require more computer power than a NAT and support fewer applications. Another potential advantage is greater security for the computers on your local network.


Point to Point Protocol software runs on a computer with a modem to provide a dial-up internet connection. For a Macintosh, different versions of PPP exist depending on the version of the Mac system software.

Some black boxes contain a utp hub, a built-in modem, a PPP server, a DHCP server and a NAT server; these boxes can connect several computers to the internet without running separate server software. In theory, you just configure it with your ISP's connection details and plug it into your phone line.


Serial line Internet Protocol is an obsolete protocol used for dial-up modem internet connections that has been replaced by PPP. Few ISPs support SLIP.


Point to Point Protocol over Ethernet is a protocol commonly used for DSL/ADSL and cable broadband connections.

Internet Connection Sharing Software

This is described in the document Sharing Your Internet Connection with an Older Mac.


AppleTalk is the network protocol used by traditional Macintosh built-in file sharing and older AppleShare servers. Traditional AppleTalk network traffic is not automatically passed across the internet so installing a network black box will not expose your local AppleTalk network to the rest of the world.


More modern Mac networks use the AppleShare/IP protocol which runs over TCP/IP. Personal file sharing in Mac OS X is based on AppleShare/IP. Unless you implement a firewall, an AppleShare/IP server can be exposed to the internet.


MacIP is an old protocol which encapsulates TCP/IP data in AppleTalk packets. It was designed to provide TCP/IP network to Macs on LocalTalk networks during the 1980s. MacIP is derived from an even older protocol called KIP (Kinetics Internet Protocol). MacIP is supported by some Mac internet conenction sharing software and by dedicated MacIP hardware severs (eg Cayman Systems GatorBox).

BootP and RARP

These are older protocols used for allocating IP addresses automatically. BootP is also used for remote (or network) booting of computers.

Copyright information: If you wish to use any images on these pages, please contact the author, Phil Beesley on