Strange network behaviour

[CallACD]

Hi folks,

I have a networking question:

I have a notebook with an integrated LAN adapter which is configured to get the ip via dhcp. The adapter is configured correctly, I can browse the internet as well as my local network.

Then I have added an USB WLAN adapter which also works fine with internet, but: I cant connect to any of my other local computers, even ping will not find the other machine.
The retrieved ip adress is the within the same subnet as the other computer.

I think I have to configure it, but where? Can you help me please?

Thanks
Michael

[Harry Kuhman]

I have a notebook with an integrated LAN adapter which is configured to get the ip via dhcp. .... I can browse the internet as well as my local network.

...USB WLAN adapter which also works fine with internet, but: I cant connect to any of my other local computers...


A bit more information is needed:

Are you using a common home dsl/cable router to connect to the Internet? What additional hardware you have is a big factor here; spell it out rather than have us guess wrong.

You stated that the wireless connection ends up on the same subnet as the other systems. Good. Now spell out what those IP addresses are (there is no security issue here as long as they are unroutable addresses; and they certainly should be). What is your net mask too? Is it the same on the other computers? Are all computers set up to use DHCP, or did you "hardwire" some addresses (which can be handy for running servers, for example)?

Are the other systems on the local network running Windows or Linux or something else? Are you running firewall software on the other systems that might be letting the wired IP address through but blocking the wireless IP address? (For that matter, I would also want to check the rules, mac filtering and the like set up in the router, but again we need to know the brand and model to even know where to start there.)

Also, I'm assuming (since I was given no real information) that a single wireless home dsl/cable router is being used and is what is assigning the dhcp addresses; but there certainly could be other configurations. Is it the router doing the dhcp? Is the router also the wireless accesspoint, or is the local network more complex? Are there any other switches or networking hardware in the system? And what are you connecting to? Spell it all out. About the only thing may you might want to keep private is the IP address that your ISP is assigning you, although it might even be good to give us the first couple of numbers in that too.

Also, you say that you cannot even ping the other systems from your wireless system. Good test. I'm assuming that you are trying to ping them by IP address, but please confirm this (and try it if you were not). My question is, can you go the other direction and ping the wireless connection by it's IP address from the other computers on the network when the wireless system is up and able to access the Internet?

[CallACD]

Hi,

Heres the additional data as detailed as I can give them:

The network looks like this:

2 Machines connected via 100MBIT LAN (cable). IPs are:
* 192.168.2.154 (Computer 1 (C1))
* 192.168.2.121 (Computer 2 (C2))

These machines are connected to a 100MBit Switch. This switch is connected to an SMC 2804WBR V2 WLAN Router and firewall. This router is connected to the DSL modem. The router is also the dhcp server.

The notebook uses an Netgear MA111 USB adapter, the IP of the notebook is 192.168.2.118 (Notebook (NB)).

All network masks are set to 255.255.255.0.

And here are the connection trials (All pings are done by ip and a second time by computer name)

C1 -> C2 ==> ok
C2 -> C1 ==> ok
C1 -> NB ==> error
C2 -> NB ==> error
NB -> C1 ==> error
NB -> C2 ==> error

All computers are able to browse and to ping servers of the internet (f. e. www.heise.de)

Some more hints on what my be lead to a solution:
- There was an existing WindowsXP on the NB which could go the internet and browse the other machines, so I think the router settings are ok (I only had to deactive encryption to get the MA111 up and running). The windows is gone after a HD crash and I hoped to need it no more, so there is currently no windows installed.

- I am using the Knoppix hd installation with kernel 3.4 from the CD (left unhanged) but of course I updated my system via apt-get (apt-get update, then apt-get upgrade)

Do you need more specific information? Thanks so far
Good night
Michael

[Harry Kuhman]

Wow, what a puzzle. So far it all looks right, but clearly you should be able to ping any system by IP from any other system. The fact that you can get to the Internet from the wireless notebook makes me dismiss any of the usual Linux/Knoppix USB NIC issues, as that is clearly working. The same holds true for the many networking problems often seen after installing to HD.

You didn't mention the OS on C1 and C2, nor talk about firewalls. Are both C1 and C2 running XP? Did you install the recent SP2 so-called upgrade? If so, did you have this problem before installing SP2, or have you only tried setting up the wireless connection since accepting SP2? SP2, in addition to having some "compatability issues", is said to turn on the XP firewall by default (it was there but disabled by default previosly). If all of this is the case you might want to try disabling the XP firewall (it's not well regarded anyway) and seeing if the problem persists. In any case, I would (and do) use a different firewall than the MS firewall, there are several better free ones out there. By the way, the firewall I use would need a rule to let the incoming ping in. So if my computer was C1 you could not ping me unless I allowed it (I do allow it for "trusted" computers in the 192.168.xxx.xxx range), but the MS firewall very well might not. However I don't see why this would prevent the ping that originates at c1 from working, particularly if c1 can ping c2 (but maybe Linux and XP are using different types of ping packets and MS is only letting their own through).

You mentioned the switch. I'm guessing it's only being used because there is a long run to the room where c1 and c2 live, as your SMC router should have a 4 port switch built in. I doubt there is any problem with the switch, but you might want to try bypassing it by plugging c1 and.or c2 into the SMC just to be sure.

I have not used your particular SMC router. The SMC router I have used is somewhat limited on it's ability to filter. For example, there is MAC filtering but it applies to everything, not just the wireless section (makes setting up the MAC table a lot more of a pain, and something you have to fool with every time you change anything on the network. There is no comment field that lets you track which MAC is for which computer either!) You're not trying to use MAC filtering, are you? I don't see how I could create the problem you are seeing by MAC filtering, but it seems worth asking. Same for any other filtering you might be setting up in your router. You have no MAC filtering, access control rules or scheduling rules that we should know about, do you?

By the way, you're sure of the IP addresses and have checked them when you did this. right? I expect you know enough to recheck this, but I ask only because the SMC router I have used has real problems in fixing an IP to a computer; if the system is restarted different internal IP addresses can be given out, which makes for real problems in the routers table for forwarding services. If you just note what IP address a computer was assigned, you can't be 100% certain that it will get that address by DHCP again. Since you seem to have the IP addresses scattered across the range of available addreses, rather than given out in a logical order, I'm guessing your SMC router works much like the one I used. For me this is a real downside to the SMC routers, as I have been unable to give out IP adresses in a logical and sequential order and keep them assigned where I want them, even after playing tricks like limiting the range of valid IP addresses, starting the next computer, then enlarging the IP pool by one address and start the next computer. Once computers are restarted SMC will not put them on the same IP addresses (mucking up the forwarding tables in the router for what SMC calls "virtual servers") even with lease time set to forever.

If your SMC firewall works like the one I have used it has a section for firewall/intrusion detection where there is a radio button for "Discard ping from WAN". I doubt very much that this is the issue (it shouldn't be as it should in no way affect the lan), but it might be worth turning this off. It's worth noting here that with your switch in the network the C1 <-> c2 pings never get to the router, so it might be something other than just a wireless issue (another good reason for doing the tests without your switch if that's physically reasonable).

After the above stuff is looked at, unless someone else can join in with some good suggestions, it seems like the next thing to do might be to sniff the wire. Do you have access to a hub (a switch will not work for this)? I would be interested in seeing what was on the wire between the switch and the router as c1 tried to ping NB and as NB tried to ping C1 (you could run ethereal on C2 and watch this traffic if you could insert a hub between the switch and the SMC, or even between the switch and C1). At the very least this would tell us if the ping isn't getting to the other system or if the reply isn't going back. It would rule out a lot of maybes and point us in the right direction.

OK, one last though. If you are running XP on C1 and C2, then let us get Microsoft out of the equation. Boot your Knoppix CD on C1 or C2 and see if that changes things. Once you boot Knoppix, first confirm that the network is woring on that system by getting to the Internet, then do the ping tests again. Can you now send or receive pings between NB and C1/C2?

[CallACD]

Hi again,

Sorry for the delayed answer, but I was not at home for some days...

Here are the latest results:

The used OSses:
C1: Win XP SP1 + latest Hotfixes. No SP2, no Firewall, but NOD32 antivir
C2: Kanotix 06-2004 HD install

Win XP SP2 is not the problem here, because I havent installed it...

I have tried to connect the C1 directly to the SMC but the result remains unchanged.
I also have checked the SMC configuration:
- MAC filtering is off
- I temporarly deactivated the firewall, but no change
- I deactived the "discard ping from wan" but no change

I ran ethereal and: The apm packets are retrieved and answered. hmm
I checked all settings in the smc router and the lsat thing I could think of was to reset the smc router - and after it rebootet it all works!

Dont ask me why but thank you very much for your work and your final hint to get it!

Good evening

Cioa
Michael

[Harry Kuhman]

I ran ethereal and: The apm packets are retrieved and answered. hmm
No problem on the delay; we all sometimes have to do something else than play with our toys.

hmmm is right about this sniffing. Assuming you are really sniffing the wire with a hub, that's pretty hard to understand this is happening and the system still failed. I would have wanted to know what happened in each direction though; C1 pinging NB and NB pinging C1. I'm guessing this was a result of NB pinging C1 (which would still give the SMC one last shot at killing the packet; the other way it would seem it would have to make it at that point.



.. reset the smc router - and after it rebootet it all works!l

Wow, I wouldn't have guessed that. Congratulations. Thanks for posting back the final results.