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empedia
2005-09-02, 07:54
I have an SB2 which I have connected to a PC via a cross-over cable so that the SB2 is acting as a wireless bridge.

This is working fine - the SB2 is at IP Address 192.168.0.54 and the PC is at 192.168.0.55. The PC is configured so that the SB2 is the default gateway and I can browse the net from the PC etc. with no problem.

In the fullness of time I intend to set this PC up as a dedicated slimserver box.

The problem comes when I try to ping this PC behind the wireless bridge from another PC - IP Address 192.168.0.35. My other PC's simply refuse to see it - all PC's are connected to the same wireless network as the SB2 etc.

However the PC connected behind the bridge can ping and see all the other PC's with no problem.

Both PC's are in the same Windows XP workgroup and indeed in the workgroup the second PC can see the first PC with no problems but cannot use TCP/IP to access it.

All PC's and the SB2 are configured with the same subnet mask 255.255.255.0. The SB2 and all the other PC's are configured to have the default gateway of the Router - 192.168.0.1. All IP Addresses are static and the other PC's have no problems seeing the SB2 or the router or the internet etc.

What am I doing wrong here or will the wireless bridge effectively hide the second PC from any other PC's on the network - clearly not an acceptable situation.

I'm 99% certain this is not a firewall issue either as the second PC can see other PC's on the network with ease.

I'm going slowly mad over this so any help gratefully received.

TIA,

Matt

seanadams
2005-09-02, 09:23
The PC is configured so that the SB2 is the default gateway and I can browse the net from the PC etc.

This is wrong, although it doesn't explain the bahaviour you're seeing. I'm surprised you're able to browse the net from that machine. The default gateway setting for ALL machines on the LAN, including this one behind the SB2, should be set to your router's address: 192.168.0.1.

MrC
2005-09-02, 10:22
This is wrong, although it doesn't explain the bahaviour you're seeing. I'm surprised you're able to browse the net from that machine. The default gateway setting for ALL machines on the LAN, including this one behind the SB2, should be set to your router's address: 192.168.0.1.

Yes indeed. Is slim acting as a proxy packet forwarder in bridge mode?

empedia - you need to understand that by placing a different gateway IP on your first pc, you are trying to have the SB2 act as a router. However, since both sides of your bridge are on the same subnet, no routing is required. Packets for the same subnet are just dumped on the wire, and each device on that wire (or wireless "virtual wire") listens for its mac address and matches its IP address later - no routing required.

empedia
2005-09-02, 13:49
Hi,

Thanks for your comments. I've since changed the gateway on the bridged PC to point at the router. This was how I had it originally anyway.

Unfortunately this has not had any effect on the main problem. Effectively even though the bridged PC is in the same subnet etc. and has the same gateway now, it is effectively invisible to the rest of the network although it can see the other PC's going the other way.

This has got me stumped. If anyone else can replicate the problem I'd be very interested to hear it.

Thanks a lot,

Matthew

empedia
2005-09-04, 23:31
OK,

I have since posted this as a general problem on another forum and the consensus is that the wireless bridge is doing some kind of hiding or network address translation on the bridged PC.

Could someone from Slim Devices confirm is this is the case and is expected behavior or not please and more importantly is the bridge configurable in anyway to enable the required functionality.

Thanks a lot,

Matthew.

seanadams
2005-09-05, 01:23
AFAIK there is no inherent limitation in our bridge capability which should cause this. Older 802.11 bridges (such as the Linksys WET-11) used a technique called "layer 2.5 NAT" to get around a limitation in 802.11 chips that only allowed them to present a single MAC address to the access point- in that case this might be expected. However, this does not apply on Squeezebox2 - it's supposed to work just like an ethernet switch, i.e. transparently.

I seem to remember we verified the specific scenario you're describing and found no problems, because we wanted to make sure that a PC running SlimServer (a "HTPC" for example) could be connected by ethernet to a Squeezebox2, which would in turn provide wireless access to the server. I'll double check - we may need to have another look at it.

In the mean time if anyone can confirm/deny this behavior, it would be helpful. This may be specific to your access point or network setup.

empedia
2005-09-05, 02:54
I've done some more testing on this to eliminate my access point etc. I set up an ad-hoc wireless network and connected to it from the SB2. I get exactly the same behavior as before.

There are no other devices on the network that I know of which might interfere with the working of this so I can only conclude that this will not work the way I want it to unless I hear otherwise.

One other thing I should mention is that I have firmware 15 installed on the SB2 - maybe I should try a later firmware perhaps - would this be worthwhile.

seanadams
2005-09-05, 05:58
I've done some more testing on this to eliminate my access point etc. I set up an ad-hoc wireless network and connected to it from the SB2. I get exactly the same behavior as before.

There are no other devices on the network that I know of which might interfere with the working of this so I can only conclude that this will not work the way I want it to unless I hear otherwise.

One other thing I should mention is that I have firmware 15 installed on the SB2 - maybe I should try a later firmware perhaps - would this be worthwhile.

OK we'll look into it. I don't think upgrading the firmware would make a difference - nothing's changed in the TCP/IP/wireless code recently.

MrC
2005-09-05, 08:06
I can confirm that bridging works as desired by empedia, but can also confirm that slim is showing the same Mac address for itself (.145 ip below) and the device on the ethernet port (the .150 address).

192.168.2.145 00-04-20-05-b8-2c dynamic
192.168.2.150 00-04-20-05-b8-2c dynamic

empedia
2005-09-05, 08:13
MrC,

Are you saying that you can ping both the SB2 and the PC behind the bridge successfully from another PC on the network. If so can you post the details of your setup.

What are the ramifications of the same MAC address for the bridged PC and the SB2

Thanks,

Matthew.

MrC
2005-09-05, 08:25
Yes, I was able. I could ping to/from either side of the SB2. I was able to use higher level protocols, like Windows Sharing as well. From my main PC, I was able to navigate the Windows network to my laptop attached to slim's ethernet port. Slim itself is wirelessly connected.

The SB2 appears to be spoofing the Mac address and translating back. It must be handling incoming packets for devices on the ethernet port when bridged, and forwarding them along.

Some devices on the wireless side of the net (be they wireless or not) might have trouble with devices that have more than one IP address on the same subnet. Maybe this is why you are having trouble. Someone elsewhere in a forum had suggested some routers would need to be configured to allow Mac passthru - don't know if you're router/ap has such a setting.

empedia
2005-09-05, 08:35
Hmmm. This is strange. I've eliminated my router/access point as the problem by setting up an ad-hoc network with the same results.

Did you use static IP addresses or DHCP allocated

I'm only using intel x86 PC's on either side of the bridge so I don't imagine its anything arcane like that. I think I might try connecting a different PC behind the bridge and see what that does.

I assume you are just using a vanilla SB2 with no firmware upgrades past 15 etc - although it seems that shouldn't make any difference either.

If the SB2 is spoofing the MAC address etc. how does the MAC address resolve to the correct PC - i.e. when I ping my bridged PC how does my PC know to "route" the ping via the SB2 - if that makes sense?

MrC
2005-09-05, 10:06
Did you use static IP addresses or DHCP allocated
Wouldn't matter - this is a higher level protocol, and how the IP address gets allocated is irrelevant.


I'm only using intel x86 PC's on either side of the bridge so I don't imagine its anything arcane like that. I think I might try connecting a different PC behind the bridge and see what that does.
Also wouldn't matter what chip/architecture you are using. You're grasping at straws.


I assume you are just using a vanilla SB2 with no firmware upgrades past 15 etc - although it seems that shouldn't make any difference either.
Vanilla SB2, but I'm using the latest 6.2beta, with firmware 19. Dean suggested there have been no TCP/IP firmware changes since 15, so it probably wouldn't help resolve the problem you are seeing.


If the SB2 is spoofing the MAC address etc. how does the MAC address resolve to the correct PC - i.e. when I ping my bridged PC how does my PC know to "route" the ping via the SB2 - if that makes sense?

The PCs on either side wouldn't know - they just see the slim as the destination. But packets do contain both a Mac address and an IP address, and certainly slim sees this IP address and can forward to the correct PC. A device is uniquely identified by its IP/Mac address.

You can install Ethereal on your non-bridged PC and see what packets slim is forwarding to it.

empedia
2005-09-06, 03:07
I think I have this fixed now - if Windows Firewall is enabled on the bridged PC then nothing will get through even from PC's on the same network, same subnet etc.

Disabling windows firewall allows me to successfully access the bridged PC. I wish Windows Firewall had the ability to let through anything by IP address etc.

Anyway thanks to everyone for their help.

Matt.

MrC
2005-09-06, 08:42
I think I have this fixed now - if Windows Firewall is enabled on the bridged PC then nothing will get through even from PC's on the same network, same subnet etc.

Of course! That's what firewalls do. Until you configure them otherwise, most block everything incoming by default, and are less restrictive outgoing. Your outgoing ping works with the firewall enabled because the connection was initiated by the stateful firewalled PC, and the firewall maintains a connections table. But incoming traffic like your ping from the other PC across the bridge is blocked by the firewall.

Being 99% certain can often lead to misleading diagnosis.

Glad its working of you!