Problems with a switch

  • Thread starter vasilijepetkovic
  • Start date
V

vasilijepetkovic

Hello All,

I work in a group with four people and we have one internet connection.
So we bought a switch (D-Link DSS-8+) - however we have trouble
connecting. The first person that connects to the switch is fine (he or
she has connection all the time) but other three individuals are not
able to connect.

We all use the same computers with the same config. Also, we tried to
swap and a person B, instead of person A, would connect to the switch
first - and in such case person B would have connection to the web
while everyone else (including person A) would not have access? We
repeated the same test with persons C and D and the same problem was
present: only the first person would have connection.

Can someone give us guidance in terms of how to troubleshoot this.

Best,

Vasa
 
J

Jim

A "switch" does NOT, in and of itself, allow internet sharing! It simply
allows a group of PCs to communicate WITH EACH OTHER, assuming all have
unique IP addresses. To share an internet connection, you need a ROUTER,
which contains a WAN port (to which you connect your cable/dsl modem) and
integrated switch, to which all your PCs are connected via the LAN ports.
The router then uses NAT (Network Address Translation), which takes the
single IP address provided to the router at the WAN port, and allocates
local IP addresses to all your PC.

Sounds to me like your trying to take a simple switch and have it act as a
router. You can't. You need a router!

Jim
 
D

David Maynard

Hello All,

I work in a group with four people and we have one internet connection.
So we bought a switch (D-Link DSS-8+) - however we have trouble
connecting. The first person that connects to the switch is fine (he or
she has connection all the time) but other three individuals are not
able to connect.

We all use the same computers with the same config. Also, we tried to
swap and a person B, instead of person A, would connect to the switch
first - and in such case person B would have connection to the web
while everyone else (including person A) would not have access? We
repeated the same test with persons C and D and the same problem was
present: only the first person would have connection.

Can someone give us guidance in terms of how to troubleshoot this.

Best,

Vasa

Your ISP provides you with one IP, for one computer, so which ever computer
gets there first gets the IP, and there isn't any more.

The problem is you have the wrong thing for connecting multiple computers
to the ISP modem. You need a (NAT) router, not a switch.

A switch simply connects the NICs together.

A NAT Router (the stores will simply call it a router as all the consumer
types will include NAT) provides NAT, Network Address Translation, so all
of the computers 'look like' one computer to the ISP modem.

NAT will provide each computer with a local IP and each computer then talks
to the router, which remembers who asked for what and then sends it to the
internet over the ISP provided IP. NAT then receives and forwards the reply
back to the computer that asked for it. Keeping track of who asked for what
and sending things to the correct place is 'routing' the data, hence the name.

The alternative is to use one of the computers as a NAT router, what
Microsoft calls ICS "Internet Connection Sharing." In that case one
computer connects to the ISP modem and then all the others connect to the
ICS computer on the local LAN. That's where the switch would go.

The downside to ICS is the ICS machine must be on and booted for any of the
others to get to the internet.
 
P

Peter

Your ISP provides you with one IP, for one computer, so which ever computer
gets there first gets the IP, and there isn't any more.

The problem is you have the wrong thing for connecting multiple computers
to the ISP modem. You need a (NAT) router, not a switch.

A switch simply connects the NICs together.

A NAT Router (the stores will simply call it a router as all the consumer
types will include NAT) provides NAT, Network Address Translation, so all
of the computers 'look like' one computer to the ISP modem.

NAT will provide each computer with a local IP and each computer then talks
to the router, which remembers who asked for what and then sends it to the
internet over the ISP provided IP. NAT then receives and forwards the reply
back to the computer that asked for it. Keeping track of who asked for what
and sending things to the correct place is 'routing' the data, hence the name.

The alternative is to use one of the computers as a NAT router, what
Microsoft calls ICS "Internet Connection Sharing." In that case one
computer connects to the ISP modem and then all the others connect to the
ICS computer on the local LAN. That's where the switch would go.

The downside to ICS is the ICS machine must be on and booted for any of the
others to get to the internet.

Not sure this is the case. I had a friend with this exact same
situation here in the UK. He had a ADSL modem that had USB and one
network socket. Originally he had it connected via USB to one computer
at a time (needing to reset modem, etc everytime he wanted to swap his
desktop for his laptop). As far as recall, I got him a network 4-port
switch which he connected the modem to, and from this he has been able
to connect at least 3 other computers simultaneously, all with access to
the internet.

As far as my thinking went, and I may be wrong but it worked anyway, the
switch must have provided the MAC address through which the modem was
quite happy to accept as being the single computer it was connected to.
Which was enough. And, of course, through the switch all traffic could
then be routed to the appropriate computer. This has worked flawlessly
for the past couple of months.

Obviously this won't work if there is no network port in the modem, but
if there is then what the OP could try is, turning off the modem
(disconnecting the power supply completely), powering up the switch and
then connecting the modem to the switch and powering it up. If he gets
solid connection lights on the modem then presumably all should be well
and he can then go ahead and try connecting each of the computers to the
switch to see if they have internet access.

Worth a try. :)
 
D

David Maynard

Peter said:
Not sure this is the case. I had a friend with this exact same
situation here in the UK.

Except it isn't the same. He was physically moving a cable because he
didn't have more than one port to connect the computer to. They already
have the switch with all of them physically connected and it doesn't work.
He had a ADSL modem that had USB and one
network socket. Originally he had it connected via USB to one computer
at a time (needing to reset modem, etc everytime he wanted to swap his
desktop for his laptop). As far as recall, I got him a network 4-port
switch which he connected the modem to, and from this he has been able
to connect at least 3 other computers simultaneously, all with access to
the internet.

As far as my thinking went, and I may be wrong but it worked anyway, the
switch must have provided the MAC address through which the modem was
quite happy to accept as being the single computer it was connected to.
Which was enough. And, of course, through the switch all traffic could
then be routed to the appropriate computer. This has worked flawlessly
for the past couple of months.

Switches aren't routers.

His modem, with both USB and ethernet, must have NAT built in so all that's
needed is more ports, e.g. the switch.
 
B

Brad Houser

Not sure how the OP differs from my friends. Are there 2 different
types of ADSL modems out there?

At least two. Internal and External. Those without routers and those with.
Your friend's sounds like an external dsl modem with router, similar to
this: http://www.techdepot.com/product.asp?productid=3443449&affid=10000485
(Is this the NAT facility you
mentioned?)

NAT is short for Name Address Translation, it is what allows you to share
one internet connection with multiple computers. It is done in the Router.
It basically keeps track of every packet and redirects it to the correct
computer, but your ISP thinks you have only one IP address. The "local" IP
addresses are private, and have number consisten with private IPs
(192.168.x.x for example). Private IP addresses are not unique, and they
can not be reached directly because of that.

So, it really only wanted to allow 1 computer connected at a time which
makes me wonder where it was getting the MAC address from when going
through the switch. If it was fetching this from the first computer
that was connected when the network was set up, then I would have
thought that still only that computer would have been allowed to connect
to the internet. So how was it resolving the requirement for a MAC
address? And, if from one of the computers in the network, then how
were the other computers (with different MAC addressess which should
have caused the modem to refuse to allow traffic to/from I would have
thought) able to send/receive data?

Routers can be configured to only allow certain MAC addresses, or any. That
may explain why it had to be reset. The other thing that might have worked
is to repair the IP connection, in which case the new computer requests a
new IP address, and the router gives it to it.

Brad H
 
D

David Maynard

Peter said:
Not sure how the OP differs from my friends.

They already have the switch and your friend didn't.
Are there 2 different
types of ADSL modems out there? (Is this the NAT facility you
mentioned?)

Yes. Some have NAT and others don't. Depends on whether they were intended
to support one, and only one, computer or if they have provisions for more
than one, meaning NAT built in. Look up the specs for the modem and it
should say so.
Certainly the OP didn't mention what was being used to
connect with, but presumably it was connected directly to the switch in
order to try to allow more than one computer to make use of it.

They wanted all of them to work but only the first one that tried to, and
subsequently did, get a connection did work with 'connection' being the NIC
saying it's 'connected', which means it got an IP from the DHCP request.

They're just booting the machines (or enabling/disabling the NIC, or
plugging cables) and observing which one works: the first one up.
Not sure I quite understand why my friend's computer worked. I do know
that if you tried connecting the modem to a different computer then it
wouldn't work until you reset the modem (by completely powering it down)
because it was locked into the MAC address of the previous computer.

Yes, some do that. The ISP also checks the MAC at their end. It's how DHCP
keeps track of assigning IPs.

So, it really only wanted to allow 1 computer connected at a time which
makes me wonder where it was getting the MAC address from when going
through the switch. If it was fetching this from the first computer
that was connected when the network was set up, then I would have
thought that still only that computer would have been allowed to connect
to the internet. So how was it resolving the requirement for a MAC
address? And, if from one of the computers in the network, then how
were the other computers (with different MAC addressess which should
have caused the modem to refuse to allow traffic to/from I would have
thought) able to send/receive data?

Hope you can explain, or direct me to somewhere on the web that can do
so.

It's hard to explain what your friends system did when there's no
description of the equipment but a switch doesn't do NAT. Maybe you got a
router thinking it was a switch. Maybe it was a router with a switch, a
common situation, and that made you think it was a switch. Maybe you really
did get a switch and the modem had NAT. I can't tell without any model numbers.

What I can say, though, is if you have a typical DSL/Cable line that
provides only one IP then you have to have NAT somewhere, either in the
modem, standalone NAT router, or ICS in one of the computers, to connect
more than one computer to it and a switch won't work because it doesn't do NAT.

Consider: Each computer needs an IP and if the ISP provides only one then
where do the others come from? The NAT router. But switches don't have a
DHCP server and don't assign IPs... nor do they do NAT. They can't possibly
work unless there's NAT somewhere else, e.g. in the modem.

The other possibility is paying the ISP for more than one IP but since that
costs money I'd think one would know if they're paying for it.

(When I say NAT router I am speaking of the typical 'router' sold in
consumer stores that is actually a multifunction device including a router,
NAT, DHCP server and, usually, a firewall. A switch is just a switch.)
 
P

Peter

Except it isn't the same. He was physically moving a cable because he
didn't have more than one port to connect the computer to. They already
have the switch with all of them physically connected and it doesn't work.

Not sure how the OP differs from my friends. Are there 2 different
types of ADSL modems out there? (Is this the NAT facility you
mentioned?) Certainly the OP didn't mention what was being used to
connect with, but presumably it was connected directly to the switch in
order to try to allow more than one computer to make use of it.
Switches aren't routers.

His modem, with both USB and ethernet, must have NAT built in so all that's
needed is more ports, e.g. the switch.

Not sure I quite understand why my friend's computer worked. I do know
that if you tried connecting the modem to a different computer then it
wouldn't work until you reset the modem (by completely powering it down)
because it was locked into the MAC address of the previous computer.

So, it really only wanted to allow 1 computer connected at a time which
makes me wonder where it was getting the MAC address from when going
through the switch. If it was fetching this from the first computer
that was connected when the network was set up, then I would have
thought that still only that computer would have been allowed to connect
to the internet. So how was it resolving the requirement for a MAC
address? And, if from one of the computers in the network, then how
were the other computers (with different MAC addressess which should
have caused the modem to refuse to allow traffic to/from I would have
thought) able to send/receive data?

Hope you can explain, or direct me to somewhere on the web that can do
so.

Thanks.
 
P

Peter

Anyway, I'm going to try and pop round to get some better details about
the modem and how things were connected. Perhaps that may help explain
what the difference is.
Whoops!! Called my friend up and asked him. He told me it said on
device '4-port broadband router'. And I got him the damned thing!!
Geez my memory ain't what it used to be. Apologies for wasting
everyone's time.
 
D

David Maynard

Peter said:
Whoops!! Called my friend up and asked him. He told me it said on
device '4-port broadband router'. And I got him the damned thing!!
Geez my memory ain't what it used to be. Apologies for wasting
everyone's time.

No sweat. It happens to all of us from time to time ;)
 
P

Peter

At least two. Internal and External. Those without routers and those with.
Your friend's sounds like an external dsl modem with router, similar to
this: http://www.techdepot.com/product.asp?productid=3443449&affid=10000485

Sorry, nothing like it. See below.
NAT is short for Name Address Translation, it is what allows you to share
one internet connection with multiple computers. It is done in the Router.
It basically keeps track of every packet and redirects it to the correct
computer, but your ISP thinks you have only one IP address. The "local" IP
addresses are private, and have number consisten with private IPs
(192.168.x.x for example). Private IP addresses are not unique, and they
can not be reached directly because of that.




Routers can be configured to only allow certain MAC addresses, or any. That
may explain why it had to be reset. The other thing that might have worked
is to repair the IP connection, in which case the new computer requests a
new IP address, and the router gives it to it.

Not sure this is what is happening. The modem came from the ISP when
the subscription was setup. It is a very basic USB modem. You cannot
log into it via an IP address in order to configure it. It just also
had a network port if you preferred to use that instead of the USB
interface to allow it to connect to your computer.

Here's a picture that's similar, though this one appears to not include
the RJ45 connection.

http://www.dsl-warehouse.co.uk/product.asp?pr=ST330

When we first tried to connect to a different computer directly, and it
didn't work, we had to phone the ISP's tech support who explained that
it works through the MAC address and that was why it needed completely
powering down so that it would have to re-determine the computer's MAC
address that was being connected through it. Without that powering down
it still had details of the previous computer's MAC address and would
refuse to allow an internet connection. That is what I was told by tech
support.

Anyway, I'm going to try and pop round to get some better details about
the modem and how things were connected. Perhaps that may help explain
what the difference is.

Still, as far as I can see, the OP still hasn't mentioned the type of
modem that was being used, so we have no way of knowing where the
differences lay.
 

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