Switches on a satellite network

Posted on 2008-11-14
Medium Priority
Last Modified: 2013-11-09
I need help! I work in Afghanistan,  and I've never seen a network set up this way. I have a vendor that is providing in room internet services to the military staioned in 5 camps here in Afghanistan. In more than one instance, they run fiber to a central point, then from there, it goes into a Netgear 8 port 10/100 Mpps switch. What the issue is, in most cases it's dasiy chained, and well over a hundred of the Netgear switches are used.  What is the maximum number of these switches that can be used and not cause problems? The switches are left outdoors, in little metal boxes, not protected from the heat/cold. Many issues here, this is just the start! Thanks
Question by:gedavis4704

Accepted Solution

larsga earned 500 total points
ID: 22966863
You can, in theory, daisy chain as many switches as you want. There are however some practical issues that can cause problems. Not knowing how many (and what kind of) devices that are connected to this network, the below might or might not be potential issues.

First of all, with an all-switched network everything is in the same broadcast domain. That is, if a device on the network sends a broadcast packet, it will be forwarded to all other devices. On a large switched network this can cause problems, since you run the risk of broadcasts taking up a considerable amount of the available bandwidth. For example, Windows machines will regularly send broadcast packets to tell other windows machines on the local network that it is there. So if you have many PCs/devices that regularly send broadcast packets connected to this switched network, this might be an issue.

Second, the switches' MAC address tables might get exhausted. To explain what and why this might be a problem, we need to get into how switches work. In the old days, we had hubs. A hub is just a dumb repeater, when it receives traffic on a port, it will just repeat it out all the other ports. Switches are smarter, they look at the destination MAC address when determining which port to send the packet to. In order to do this, a switch will build a list of which MAC addresses it sees on which ports. The problem is, this address table is limited in size (depends on make and model of the switch, cheap home switches typically have a lot smaller tables than business grade gear). So if there are too many devices on the switched network, you risk MAC address tables overflowing on some (or all) of the switches. If this happens, most switches will revert back to old dumb hub mode (in effect, they will treat all packets as broadcast packets).

On a switched network all devices can see each other directly. Can be very convenient if the goal is to get stuff up and running with as little hassle as possible, but it makes it harder to do stuff like security. Cable loops, bad connections/cables and misbehaving client devices are also harder to detect and isolate.

The alternative is to add some routers here and there to keep the size of each switched network at a reasonable size. However, routers are a bit more complicated and one needs to do a bit more work with setting up routing and dhcp.
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Expert Comment

ID: 22967781
I've seen setups similar to this. It's obvious this has been done as cheaply as possible. They probably don't want to have to do any rewiring necessary to change it.

Of course there is some logic to using inexpensive switches. If your equipment is going to be in a harsh environment you know it won't last long. A netgear may not last as long as comething like a Cisco, but for the cost, you could replace it many times for less than the cost of the Cisco.

Author Closing Comment

ID: 31517044
Thanks, these guys put the network up in a rush, leading to a terrible setup, going to take a lot of work to get it running smoothly.

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