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Wireless bridge(?) between office & mobile work trailer

Hello Experts,

I think I have a fairly unique situation that I would like to find the best solution for.

I have an office network made up of desktop and laptop computers that connect to a single wireless router (either via wired or wireless ethernet) and am using a cable modem for internet connectivity.

I also have an enclosed trailer that I work out of at remote sites.  It will also have desktop and laptop computers networked via wired and wireless router.  When I'm mobile, I will use the wifi hotspot on my Droid X to get internet for my work trailer.  My main desktop computer in the trailer will have both a wired ethernet card (connected to the router so it can talk to other computers), and I will also be putting a wireless network card in it so I can also connect to my Droid when needed and get internet.

I have created a diagram of what I'm trying to do if it will help describe things better than I can with words:


What I want to be able to do is when my trailer is parked at my office, I want the two routers to be able to "bridge" together so that I can transfer files to and from the trailer and the office.  I also want to be able to get on the internet in the trailer without having to get out my phone (i.e. when trailer is at the office, I would like for the computers in the trailer to be able to access the internet via the cable modem in the office).

I have a couple of wireless routers that I can use now, but I don't think they will do what I want to do.  I am willing to buy whatever I need to buy to make this setup happen.

When the trailer is not at the office, these two will obviously operate completely independent of one another.  I'm assuming each router will need to be able to handle DHCP requests independently, and each will have it's own subnet.  But when they come together, I want them to "bridge" together so they act like one big network.

Is this doable?  If so how and what do I need to buy to make it happen?


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1 Solution
jmeggersSr. Network and Security EngineerCommented:
This is definitely doable.  You just need wireless devices that can be in bridge mode.  I know the Cisco 1240 APs will do this, but I'm sure there are others as well.  

There are a few ways of handling routing, but your network is small enough it's probably just as well  to manage it ad hoc.  When the bridge is active, everything will be on the same LAN, just make sure your DHCP is handing out the same subnet on both sides.
JahelkaAuthor Commented:
OK, so I DO want them to be on the same subnet.  That is a good piece of info.  I assume I just set each router up so DHCP hands out a non-colliding range of IPs...

What I really don't want to have to do is reconfigure the router depending on whether the trailer is at the office or it is out and about.  When you say ad hoc and bridge mode, does that mean that there is no solution that will allow me to do this fairly seamlessly, or at least, without reconfiguring one or both of the routers depending on whether the trailer is in range or not?  I'm going to need a little more explanation than you gave me I'm afraid before I fully understand how I'm going to do this and how it will work.


jmeggersSr. Network and Security EngineerCommented:
If you're truly bridging the LANs, then yes, the bridge will be at layer 2, and the IP addresses on both sides of the bridge will be in the same subnet.  Your assumption about DHCP is exactly the way I would handle it.  Of course, you could introduce routing into the picture, but it complicates things, the bridge itself will still be at layer 2, and you'd need additional equipment to handle it.

The only issue is what address space your Droid hands out when you're using that.  If you can control that, then it makes it easier; if you are locked in by one of the devices, then you have to adjust accordingly, and if you're locked in on both ends and they don't agree, then you'll have to do something creative.
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JahelkaAuthor Commented:
I'm afraid I'm not as smart about setting this up as you are giving me credit for.  I've set up routers many times before.  Once even to do VPN/IPSec over the 'net to connect two remote networks together.  But I've never set up TWO routers at one location before and had to make them talk to one another.  And I certainly haven't done anything like that wirelessly.  I understand subnets, dynamic vs. static IPs (DHCP), and the differences between a router and a switch.  But I don't understand "layer 2", or the difference between a bridge and an access point (all the definitions I have looked at are very vague).  I believe the only reason I'm having to ask this question is because I don't know what terminology describes what it is that I want to do, therefore it is difficult for me to search for!

I looked at the datasheets on a Cisco 1242AG.  First off I was rather put out by the price tag (looks like these are over $350 each).  I was thinking I would be able to do this for a few hundred bucks, not $800.  Is there a certain feature set that I need to look for to be able to do what I want?  Any other hardware recommendations that might be a little less expensive, or is this it?

FYI, my Droid does allow me to specify SSID, security mode, wifi channel, and DHCP start address.  So I'm assuming I should be able to have my desktop computer in the trailer be multi-honed and be connected to both networks at the same time.
jmeggersSr. Network and Security EngineerCommented:
If you have two routers connected by an Ethernet cable, and both connections are on the same IP subnet, that's a layer 2 connection.  Same thing if you have multiple devices on the same IP subnet connected by a switch.  If you have devices that connect to each other through a router (or a switch that's routing between VLANs), and they have IP addresses in different subnets, that's a layer 3 connection.

There probably are other devices that can do the kind of bridging you're describing, but I can't tell you what they are.  What you want to look for is a wireless bridge, most likely one advertised to extend an existing wireless network. Maybe something like http://www.newegg.com/Product/Product.aspx?Item=N82E16833127256 would do the trick.  It looks like it's designed to use a standard access point on one side and use this on the other side to plug several devices in and a have this device connect to the existing AP.  I can't say I've set one of these up, so I can't tell you exactly how it will work, but the description sounds, to me, like what you are trying to accomplish.
JahelkaAuthor Commented:
Yea, I think what I want to do is pretty screwy!  =)

I sent this query to tech support at Netgear and they gave me a very thorough response that should get me shoved in the right direction.  She basically said I should leave my existing wireless routers in place, and get two of their wireless access points (either WG102 or WG103) to "bridge" the two together.  I don't know if I'll end up buying one of those or not (they are in nice metal cases and would probably be good for a trailer that will get roughed up going down the highway).

Thanks for the clarification on the Layer 2 vs Layer 3.  Should be able to do Layer 2 with the access points/bridges (heck, I still don't fully understand the difference!).

I think I'm going to go down to my local MicroCenter and see if they have anyone there that is more of a geek than I am to make a recommendation.  That way, if what I buy doesn't work out, drive down and take them back and try something different.

Thanks for the input and the help...  I wouldn't say I have a full solution yet cause I haven't actually made it work, but I believe I'm well on my way.  THANKS!
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