Access Point problem

Rick Stevens rstevens at vitalstream.com
Wed Mar 9 18:12:18 UTC 2005


Claude Jones wrote:
> Rick Stevens wrote:

<snipped a lot of preceeding stuff>
>> How about describing your network a bit more?  What router are you
>> using?  Does it have wireless on it?  What is acting as your DHCP
>> server?  Do you want the NIC on your machine to plug into the AP
>> so your machine goes wireless?  Just what are you trying to accomplish?
>>
>>> My access point is working too well - I can get internet access
>>> from several rooms away in an industrial building with lots of
>>> concrete and steel in the walls. It's not currently locked down in
>>> any way, so I guess anyone else who tries can get in as well. 
>>
>>
>>
>> Set up a non-broadcasting ESSID and a WEP key, PRONTO!
> 
> 
> I see that more explanation is necessary. I do know that in theory the 
> access point and my LAN are on two different networks. My Linux box is 
> both router and DHCP controller.

Ah!  That's a help.  One thing...does the Linux box have two NICs in it?
If so, what are they and what IP addresses do you have on them?

>                                 In theory the Access Point is supposed 
> to be 192.168.0.50.

All D-Link access points default to 192.168.0.50/24 (meaning a 
255.255.255.0 netmask) upon a hard reset (e.g. poking a paperclip into
the "RESET" hole and holding it there while powering it up).

Provided you have access to that network (either via a route or because
your machine is on the same network), you can get to the management GUI
by "http://192.168.0.50".  Note that once you change the AP's IP address
via the GUI, it IMMEDIATELY changes to that address and you won't be
able to access it via 192.168.0.50 anymore.  Since the only way you can
manage the device is via the network, it's quite useful to put a Post-It
or something on the bottom that has its IP address written on it.

>                       My LAN is configured to 192.168.2.0/255.255.255.0. 
> Despite this, the laptop that is on the LAN is getting it's IP address 
> from the Linux box, and is getting out to the net. Somehow, this doesn't 
> make sense to me, but that's how it is.

If your Linux box is the DHCP server AND router, one NIC must be on the
192.168.2/24 network.  You didn't say what the other NIC is.  I'm
assuming it's on a public IP (perhaps via your cable or DSL modem), in
which case the laptop is sending traffic to your Linux machine and being
the good router that it is, it sends the traffic to the other NIC and
relays responses back.  That's what a router does--it routes traffic
between networks.

>                                        I did consider the possibility 
> that the Access Point got reprogrammed at some point, and is on the same 
> network as my Lan, but if it is, I can't see it - I have tried several 
> obvious addresses as Scot suggests in the next reply to my post, but it 
> doesn't respond. Is there some scan I can run to try to spot it?

Well, you could run something like this:

	#!/bin/bash
	FIRSTIP=192.168.0.1
	LASTIP=192.168.0.255
 

	IP=$FIRSTIP
	echo `date`
	while [ $IP -le $LASTIP ]; do
	    ping -q -c 1 $IP >/dev/null
	    if [ $? -eq 0 ]; then
	        echo $IP is alive
	    else
	        echo $IP is NOT alive
	    fi
 

	    let IP=$IP+1
	done

All that does is do a single ping to each IP in the 192.168.0/24 network
and report whether it gets a response or not.  Remember, that has to be
run on a machine on the 192.168.0/24 network a machine that has a route
to it AND the target machines must not have iptables rules that drop
ICMP packets.

>                                                               I have 
> also tried changing my Lan configuration to the 
> 192.168.0.0/255.255.255.0 range, but, I still wasn't able to see the 
> access point - however, I did something wrong when I made the change and 
> lost DHCP services to the laptop, so I left something out when trying 
> this, and maybe that's my problem.

The problem was that, as far as your laptop was concerned, you
disconnnected the router (you changed its IP from one on the network
with the laptop, so the laptop can't talk to it).

 >                                  I changed the configuration of eth1
> in the Network admin tool, and changed my settings in the dhcpd.conf, 
> when I tried that. Are there other settings somewhere else I missed?

Ok, as I said, which NIC is what?  Is eth0 on the wired LAN and eth1
on the WAN or what?

> While reconfigured, I did try to reset the access point with the pin in 
> the reset hole method, but that didn't change my results. Now, after the 
> supposed reset which puts the Access Point to 192.168.0.50, I've put my 
> lan back to the original settings of 192.168.2.0/255.255.255.0, and DHCP 
> to the laptop is working (it's got 192.168.2.254 assigned to it), and 
> I'm getting out to the net - this is baffling my imperfect understanding 
> of how this is supposed to work.

A drawing, perhaps?

                        -----------          --------      --------
WAN (Internet)<-->eth1| Linux Box |eth0<-->| Switch |<-->| Laptop |
                       |  (router) |     ^   --------      --------
                        -----------      |       |         ------
                                         |       |<------>| WAP  |
                                         |       |         ------
                               192.168.2.0/24--->|         ------
                                                 |<------>| Host |
                                                           ------

Does that sort of look like what you're trying to do?
----------------------------------------------------------------------
- Rick Stevens, Senior Systems Engineer     rstevens at vitalstream.com -
- VitalStream, Inc.                       http://www.vitalstream.com -
-                                                                    -
-     Make it idiot proof and someone will make a better idiot.      -
----------------------------------------------------------------------




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