posted on Feb, 25 2011 @ 07:07 PM
All right……. A multi subnet switched network.
First things first. We must get some L3 managed switches for the backbone. The zyxel, Netgear, HP, D link, juniper,or cisco, brands would be fine.
Zyxel or netgear would be preferable considering that they have DHCP servers built into the switch. Most of the others just have DHCP relay
A single L3 switch will cost around $500 and UP but each switch will support a lot of computers. You don't have to have an L3 switch for every switch
in the network. Just the ones that connect subnets.
If your L3 switch does not have a DHCP server Set up each cluster of computers around a simple network switch/hub with their own DHCP server on that
network segment. Or you can manually configure the IP of each computer so that all of them fall in the same subnet, but none of them are identical. An
old router attached to the main network switch for that segment would do. You don’t have to actually send information through the old router, just
set it up so that it can handle IP allocations on that segment. In fact, if you set it up so that you actually send data through it (from one lan port
to another), then it may screw up stuff because it will try to route some of the information to the wan port.
Set each DHCP server in the network so that it’s range doesn’t overlap with any other DHCP server. (IE) 192.168.0.X, 192.168.1.X,
192.168.2.X,…..(on and on) All with a subnet mask of 255.255.255.0
Now that you have each subnet set up. You can hook them to the L3 switches. Hook one port of the L3 switch to each hub/switch of every subnet that
will be in the larger network. If a particular subnet will be a heavy bandwidth user, then we can get into trunking, but I won’t.
If your switch supports auto DHCP allocation of each port via the connected DHCP server on that port, then good. Go with it. If not, then set each
port of the switch to an IP that is within the subnet of the network connected to that port. (ie) 192.168.0.255 for the 192.168.0.X, network. Make
sure that the IP you assign to the switch port is outside the range that the DHCP server can assign for that network segment.
Once you get the backbone switch set up to each subnet then you can set up the VLAN interfaces for each port/subnet. Sometime you have to set up the
VLANs before you can assign the IP interfaces for each VLAN. Then……. Turn on routing/RIP for all subnets. That way. A packet coming from
subnet….192.168.0.X, that has a destination IP of 192.168.24.123, can be routed to the 192.168.24.X, subnet.
When you have more than one L3 switch you can place a trunk/backbone connection between them. It can be a single GbEthernet, or it can be multiple
aggregated links forming one logical link. Then you turn on RIP for the whole network and let backbone router 1 find out which subnets backbone switch
2 has access to, and send the data destined for those subnets that way(to switch 2).
The connections between networks can be wireless, DSL, Ethernet, or fiber.
If you was really good at setting up a DHCP server then you could set up DHCP relaying on the L3 routers and have all DHCP provisioning done by one
computer. Each subnet would have a pool of IP’s to use. The DHCP server would figure out which subnet the computer is on, and from what pool to
assign it an IP from depending on which port the switch told it that the computer was on. If the switch got the DHCP request on port 34, it would tag
that information onto the DHCP request and forward it to the DHCP server. The DHCP server would look at the request and see that it come from port 34
and go…… “All right, port 34 is subnet 192.168.45.X. The next free ip in that subnet is 192.168.45.211, so I will assign that IP to the new
computer.” Then the DHCP server will send the conformation to the switch which will forward it to the new computer, and everything will go on as
Each one of the 254 computers/nodes on the subnets may be actual computers, or they could be routers, that are serving hundreds more computers. They
could be connected to the subnets via wireless, DSL, ISDN, fiber, or Ethernet. Or even dialup for that mater.
Of course, if you go to all that, then you may as well go for a DNS server that everyone in the network can point to so that you can type in human
readable addresses for the most accessed pages on the network. Things like help.com which will tell you how the network is laid out and where to find
the most active sites on the network.
Now, one may ask, where am I going to get all that crap when the SHTF?……. Well…. If you live in a big city that has large businesses and
buildings, then it’s already all around you. The example network I laid out is already a common feature of most large buildings. They already have
heavily integrated privet networks. Normally they are laid out so that they have a single, or redundant connection to the internet. If they did shut
down the internet, it wouldn’t affect the privately owned systems.
If an internet shutdown did happen, the privately owned networks would still operate fine. You could still access any web page that is hosted in the
building proper (on your privet network).
To link those buildings to expand the user base would just entail setting up DSL, wireless, or fiber connection between closely spaced buildings. The
switches capable of handling the routing are already in place, you just have to coordinate the subnets, and build the data links. People close to the
core group of buildings could gain access via wireless access points which will expand the range and user base of the network island. If any one of
the buildings had a dial up provider in it, then people could call into that provider to get access to the local network island that has built up.
If you had access to fiber, or DSL service provider assets then you could quickly lay out a MAN (metropolitan area network)
Some cities already have MANs that are isolated from the internet with a few points of contact to it. Those would still be functional after an
internet shutdown. You would just have to find the IP addresses of the websites that are hosted on the MAN in your city. If you want to set up one
that other people in the city could use, then set up the server and spread the word about the IP your web page/server has.
The possibilities are only limited by the hardware you can find.