Borrowed from my posting to ba.internet.

I have the former Enhanced DSL service from PBI/SBC which comes with
5ea static IP addresses.  We have one DSL line for the entire office
complex for a total of about 20 computahs and 5 companies.  Each
company has its own IP address and router.  To the best of Google's
knowledge, there's no similar arrangement diagrammed on the interknot.


dsl ===[  Alcatel 1000  ]==[ 8 port  ]==[router]==192.168.1.xxx
line   [DSL bridge/modem]  [ ethernet]
                           [ hub     ]==[router]==192.168.2.xxx
                           [         ]
                           [         ]==[router]==192.168.3.xxx
                           [         ]
                           [         ]==[router]==192.168.4.xxx
                           [         ]
                           [         ]==[router]==192.168.5.xxx


The 5ea assorted routers need not be identical.  In my mess, it's two
Sonicwall SOHO routers, one DLink DI-604, one Netgear RT-314, and a
FreeSCO Linux router.  At $50/ea, the "extra" routers are of trivial
cost.

There is no requirement for using unique class C IP blocks for each of
the LAN's.  They can all be identical.  However, it make keeping track
of machines a bit easier and adds an additional layer of protection to
prevent "accidental" sniffing of one of the other LAN's via patching
the LAN's together (usually via wireless).

I have a dedicated management workstation (ancient P75 laptop with 2ea
ethernet ports) plugged into the hub to sniff traffic.  It belches an
alarm (MRTG SNMP trap) if the traffic is excessive as commonly found
in worms and Kazaa.  In effect, it's a crude intrusion detection
system.  That's why I use a hub instead of a switch.  If you have no
interest in monitoring traffic, I suggest a switch instead.  (The
landlord took one look at a 3Scum 24 port managed ethernet switch
decided that he didn't want that big noisy thing in his nice quiet
phone room).

The above arrangement is for BRIDGED service, and will need some
radical modifications to accomidate SBC's rediculous 5ea IP ROUTED
service.  I previously posted a proposed arrangement that would work
with SBC's 5ea IP service, that requires an additional Netopia router.

http://www.google.com/groups?selm=m0j8rv4bvp72f0s3tgq2igkpmif0fea049%404ax.com
I still haven't tested it. (Holidaze, vacation, and lack of urgency).

Anyway, that's how to share a single DSL line properly, with 5
different businesses.  Each business can run its own servers, have
their own domains, deal with their own port forwarding, and basically
have the equivalent of a dedicated connection, sharing only the
bandwidth.  Plop a drawing on your web pile and proclaim that you can
save business owners and neighborhood DSL co-ops some cash.

======================================================================

Here's another example of what can be done with 5ea static IP's.

The customer wanted to offer free wireless internet access, but didn't
want the wireless customer to see his office computahs.  With one IP
address, this would have required a DMZ, which would interfere with
his port redirection configuration if he had only one WAN IP address.
I decided that it was easier to simply have a seperate WAN IP address
for the office and for the wireless, each with their own router.


dsl ===[ DSL  ]==[ 5 port ]==[office]==192.168.1.xxx (office LAN)
line   [ modem]  [ethernet]  [router]
                 [ switch ]
                 [        ]==[wireless]==192.168.2.xxx (laptops)
                 [        ]  [router  ]
                 [        ]
                 [        ]==[wireless]==192.168.3.xxx (laptops)
                 [        ]  [router  ]

With this arrangement, the office LAN is totally isolated from the
wireless LAN and the wireless customers never see the office network.

The wireless router is actually an ethernet router (DI-604) and a
seperate wireless bridge (DWL-900AP+) with power over ethernet
adapters, which gives me the flexibility of locating the radio/antenna
in the ceiling area.

Sometime next week, I'll be installing a 2nd radio to deal with
coverage issues between the first and 2nd floors.  I'll be using
Linksys BEFW11S4 wireless router (which the owner picked up cheap
somewhere).  It will also have its own IP address as there is no
interest in connecting between wireless networks.

So, the pitch line is that multiple static IP's offer isolation and
security between different parts of a LAN and are useful for
do-it-thyself coffee shop shared DSL wireless service.


-- 
Jeff Liebermann  150 Felker St #D  Santa Cruz CA 95060
(831)421-6491 pgr  (831)336-2558 home
http://www.LearnByDestroying.com   AE6KS
jeffl@comix.santa-cruz.ca.us   jeffl@cruzio.com