Multi-NIC Gateways and Related Advanced Configuration Techniques
Unfortunately, many people more familiar with other platforms,
such as Unix or Windows, are either skeptical that Apple's Open
Transport networking software can handle true IP multihoming using
multiple NICs and/or are unaware of the networking capabilities
a Mac using IPNetRouter has. Further, some users familiar with both
Mac's and IPNetRouter are not aware of exactly how to use some of
IPNetRouter's more advanced capabilities. I dedicate this chapter
to both groups. This chapter presents an example of mult-NIC Powerbook
Firewire 2000 for IP routing and NAT Mac using a combination of
3rd party drivers and NICs. Some of the nuances of both Open Transport's
IP multihoming capabilities and advanced use of some of IPNetRouter's
interfaces is explained but this is by no means exhaustive. In general,
its to encourage those users who did not know or did not know how
IPNetRouter could be used to solve networking solutions of a more
Tutorials for configuration of simpler Internet sharing LANs with
IPNetRouter are elsewhere located in the IPNetRouter guide. This
chapter is not recommended for users just becoming familiar with
Internet sharing, the Internet protocol, and networks. If you are
interested in exploring what IPNetRouter and Open Transport are
capable of, read on forwarned that this chapter covers advanced
concepts in IPNetRouter and Open Transport, as well as IP routing
and other related topics. It is written in a "shotgun"
style; that is, a complex routed NAT WAN configuration is presented
first and then explored in detail.
Demonstration of a Complex Gateway
Apple's Open Transport is capable of having more then one logical
IP interface (aka virtual IP interface) on a physical networking
port (a "NIC") and routing between them. IPNetRouter,
through its NAT module, can perform IP Masquerading on up to four
NICs. In addition, many logical interfaces can be added to each
NIC. We start off with Figure aaa, an IPNetRouter's Interface window
for a Powerbook using five NICs, two of the interfaces are used
to demonstrate IP Masquerading and two of the NICs also have additional
logical IP addresses added. In further sections of this chapter
some of the implications of Figure 1 are covered in more detail,
especially with regard to routing and port mapping.
Figure aaa. IPNetRouter Interface Window for a Powerbook with
Five NICs. The Powerbook is configured to route between 7
networks and the PPP and AirPort interfaces have IP Masquerading
enabled on them. Note the logical IP interfaces on the built-in
Ethernet and AirPort NICs.
In Figure aaa, all the LAN client IP devices on the various physical
network segments (Skyline wireless, Firewire, Ethernet) to which
the Powerbook is connected successfully access the Internet through
the installed AirPort card and/or modem (PPP) masqueraded IP addresses.
(Yep!) In addition, the gateway Mac is able to access and route
networks simultaneously through one or more of its nine IP address
interfaces. The MacIP dlp uses Appletalk over whatever NIC is picked
in the Appletalk control panel. The demonstrated use of the IPNetRouter
Interface window and its Config Box can be applied in configuring
any Mac gateway with other types of NICs that have IP multihoming
compatible drivers and firmware. The performance on all networks
is limited generally by the bandwidth of each LAN segment and NIC
except in the older types of hardware which may be limited by the
MacOS and the version of Open Transport and associated drivers that
can be run. In this case, the 400mhz Powerbook is running MacOS
9.0.4 and OT 2.6.3 and is therefore not overly burdened for purposes
of packet routing.
TIP! To add logical IP interfaces to NICs, use the little up and
down arrows in the "Configure Interfaces" box of the Interfaces
As one can see, there are two different IP networks sharing the
builtin Ethernet NIC. Both are logical IP interfaces on that NIC,
the one without a ":[n]" is the primary IP interface for
the builtin Ethernet port. Both of these networks can exist on the
same Ethernet segment and Open Transport can route to and from both
the 10.10.10.0 and 192.168.10.0 subnets. More on routing is covered
later in this chapter.
Discussion of the topology and NIC configuration for the example
Figure bbb. Diagram of Example Topology
I picked the NICs used to demonstrate some general principals associated
with Mac networking, Open Transports capabilities, and 3rd party
solutions available for the Mac's.
Most astute readers will have noticed that I setup an IP interface
to run over the Powerbook's Firewire port. Apple does not ship software
that permits this. Fortunately, Unibrain's Firewire IP driver support
IP over Firewire! Each device on the Firewire network must be Firewire
capable and have a similar driver installed on it. In my case, I
used an iMac DV running 9.0.4 with the Unibrain driver as an IP
client--Unibrain also has drivers for Windows, and possibly other
Firewire capable hardware, etc. Check with Unibrain to find out
exactly what their IP dll supports.
Similarly, the Farallon Skyline PC card, an 802.11b wireless NIC,
uses its own drivers and software to communicate to its wireless
LAN segment--in my example, I used a 3400 with a 2mb PC card and
an AirPort card enabled iMac on channel 3. The AirPort wireless
segment used channel 8 and was completely seperate from the Farallon
NIC's LAN segment. The Skyline card will work on any portable that
supports their driver--they claim its compatible with MacOS 7.1
and later; I've only tested it with 9.0.4 and 8.6 myself.
There are four or five interesting thing about the AirPort wireless
segment. First, the example shows that IPNetRouter is capable of
sharing an IP Masqeraded interface on a wireless NIC. Apple's AirPort
software, although it incorporates some of IPNetRouter's NAT technology
is not configurable in this way. Second, the primary AirPort interface
is a dynamically assigned IP address. More on that later. Finally,
there are three logical IP interfaces that the gateway has. This
was setup in this way to demonstrate some advanced port mapping
concepts, also covered later in this chapter.
Also of note is the upstream wireless access point for this network.
I used an Apple hardware basestation in Transparent Bridging mode
connected to my ISP's cablemodem network. Other wireless routers
may also support a similar configuration--you'll have to check with
a particular devices manufacturer to see if it supports true transparent
bridging mode if you want to use a different device. See also the
AirPort chapter of this guide for more
info on AirPort and its capabilities.
The PPP and Ethernet interfaces follow the setup as covered in
the Ethernet and PPP chapter of the
guide with the exception of the additional logical, 10.10.10.1,
interface. There is more discussion of the PPP interface later on
in this chapter.
MacIP, as covered elsewhere in the manual, is limited
to whatever NIC the Appletalk control panel is set to use. In this
case, it would work over any of the present LAN segments.
Advanced Port Mapping With IPNetRouter
Mapping multiple public IPs to LAN clients
A simple mapping of all IP ports and protocols supported by IPNetRouter's
NAT module is easily possible using its Port Mapping window interface.
As shown in Figure 1 above there are three IP interfaces on the
masqueraded AirPort NIC. This means that each IP interface on that
NIC can be subjected to NAT. Let's map the two non-IP Masqueraded
IP addresses on that Interface to two LAN clients on seperate private
LAN segments attached to the gateway.
In effect this simply translates all incoming packes
Setting up multiple mapping tables
Discussion of port mapping and how to add this type of mapping.
How to add mappings to multiple Masqueraded interfaces. Exclusion
of NAT from an Interface.
Figure ???. The port mapping window with several mappings.
Advanced Routing Concepts
Discussion of routing in IPNetRouter and OT. Discussion of limitations
with regard to bandwidth teaming.
Figure ???. The Routes window for the example.
Limitations in Open Transport
Discussion of limitations with dynamic IP address NICs and other
limitations to the IP Masquerading interface. Discussion of driver
and NIC firmware compatibility.
Table ???. List of OT and Mentat equivalent implementations (and
Discussion of more advanced security implications of IPNetRouter
in various configurations.
For more on how particular buttons and other parts of IPNetRouter's
interfaces work, access the help help text via the "?"
(help) button in each IPNetRouter application's windows and see
other sections of this guide.
See the Troubleshooting and
OS 9 Compatibility section, Read Me and release notes documents
included in your installation folder, and the FAQ
page on our web site for more info on configuring your LAN with IPNetRouter,
supported NICs, etc.