MultiPort/LT User Reference
Page 24
Chapter 2
2.1.7
MultiPort/LT MacIP Operation
In order for a Macintosh to communicate with a Non-AppleTalk host it is
necessary for the Macintosh to use the same protocol that the host is using. For
TCP/IP-based hosts, this means the Mac must use TCP/IP. For a Mac
connected directly to an Ethernet, this is easy as it can (with appropriate
software such as NCSA Telnet or MacTCP-based products) directly receive and
transmit TCP/IP/Ethernet packets. For a Macintosh connected to a LocalTalk
(or EtherTalk-only) network, this is not possible.
The MacIP protocol allows IP packets to be transported over AppleTalk
networks. Note this is almost the
reverse
of IPTalk, which allows AppleTalk
packets to be transported over IP networks. The name MacIP is appropriate
because it performs the functions of the IP protocol, but over AppleTalk
networks.
Even with a protocol that allows IP packets to be transported over an AppleTalk
network, there is another simple requirement. In order for a Macintosh (or any
device) to communicate using IP, it has to first have an IP address. Allocation of
a fixed IP address to a large, fixed computer is not a problem. Allocation of a
fixed IP address to a small and mobile Macintosh does cause problems, as it
may be removed from the network on which its IP address is appropriate and
connected to one on which it isn't. For this reason, MacIP includes the concept
of Dynamically Allocated Addresses. For those applications that do require
fixed addresses, MacIP provides Static Addresses.
NCSA Telnet uses MacIP. The following example shows how NCSA Telnet
using MacTCP starts a communication session.
2.1.7.1. NCSA Telnet Operation
The sequence proceeds as follows:
1.
The MultiPort/LT registers itself as an IPGATEWAY service
on NBP.
2.
NCSA Telnet is launched on a Mac.
3.
NCSA opens MacTCP, and it looks for an IPGATEWAY and finds
the MultiPort/LT.
4.
NCSA asks the MultiPort/LT to allocate an IP address for
the Mac.
5.
MultiPort/LT gives the Mac a Dynamic IP Address from its
allowed range.
6.
The User selects an IP Host by name or IP address and opens a
session.
7.
NCSA Telnet sends an IP packet to MacTCP.
