Desktop PC to Android Mobile Hotspot - What do you use for the Gateway?

[Patrick]

Desktop PC to Android Mobile Hotspot - What do you use for the Gateway?
1. My Windows 10 desktop has no Wi-Fi card.
2. So I Ethernet out to an old router acting as a wireless client bridge.
3. This has been working for many years.

For whatever reason, the Internet went out.
So I set up the phone as a Mobile Hotspot which works for the laptop.
But I wanted the desktop to be connected also.
1. So I figured I'd set up the bridge, temporarily to the Mobile Hotspot.
2. The Mobile Hotspot has an SSID with the same passphrase as all my APs.
3. The Mobile Hotspot, by default, is set to 10 clients.

So I saved the old router configuration to the AP.
And I changed the SSID for the wireless client bridge to connect to.
Since the passphrase is the same, only the SSID needed to be changed.

Or so I had thought.
Booted many times but the router (as a wireless client bridge) won't
connect to the mobile phone (set up as a mobile hotspot).

Why not?
The only difference between the old setup & the new is the SSID.

There's also a question in the DD-WRT wireless client bridge setup of:
Local IP Address = 192.168.1.whatever/24
Gateway = 192.168.1.1
Local DNS = 192.168.1.1

I thought "maybe the DNS needs to be changed" so I changed that to
8.8.8.8 but what would I set the "Gateway" to when it's whatever the
carrier's gateway would be for the cellular data connection?

[Graham J]

Patrick wrote:
> Desktop PC to Android Mobile Hotspot - What do you use for the Gateway?
> 1. My Windows 10 desktop has no Wi-Fi card.
> 2. So I Ethernet out to an old router acting as a wireless client bridge.
> 3. This has been working for many years.
>

[snip detail]

Let's look at each component of this in turn.

The router. Conventionally a router contains 4 systems: the network
switch (so it has several Ethernet ports), the Wireless Access Point
(connecting to the network switch), the router (providing DHCP, DNS, NAT
services), and the WAN port (which could be Ethernet or a modem for
ADSL/VDSL).

The client computer. If this has WiFi it is configured as a wireless
client and only requires the SSID and key of the Wireless Access Point.
It gets everything else it needs from the DHCP and DNS services in the
router (provided the computer is set for "Auto"). If the client
computer has only Ethernet then simply plug in the cable to the router.

The hotspot. This is a router and Wireless Access Point integrated into
a mobile phone. A client only needs the SSID and key to connect to it -
everything else is provided by the hotspot. When you configure the
phone it will tell you the SSID/key that you will need. You could test
this by using a WiFi-equipped laptop. You don't need to know anything
about IP addresses. To make life easier, if you try this it would be
sensible to shut down all other computers, routers, and wireless access
points - this avoids confusion.

Your requirement is to use a conventional router as a wireless client.
This depends on the router, so you will have to refer to its manual. In
general terms, you must disable all the routing functions (DHCP, DNS,
NAT, etc.) leaving only the network switch and its internal wireless
system, which is reconfigured as a client rather than an access point.

Some routers have an option to achieve this: set the option and reboot.
Reverting to router mode may require a factory reset so find out how to
do this first. Once in wireless client mode you then have to
reconfigure the connected computer to communicate with the reconfigured
router. This might involve setting a static IP address in your
computer. Once you have communication with the router it might find the
hotspot and ask for the key, or you might have to set everything
manually. Some routers will help you with this - they get you to
configure the WiFi parameters first, then on reboot they come up
properly configured. The router should then show you that it has a
connection to the hotspot. The computer you use for this can only see
the router (because of its static IP address). So to see the internet
use another computer, or reconfigure the first as "auto". It will
communicate through the wireless client (your reconfigured router) and
get all the IP details (address, mask, gateway, DNS) from the hotspot.

Once a router is configured as a client, you can no longer use it as an
access point. So the issue of same SSIDs does not arise. If you have
other wireless clients (laptop, phone, tablet, etc.) these need to be
reconfigured to talk directly to the hotspot.

Some routers can be configured to use their wireless component to
implement their WAN port. In this case the router retains its DHCP,
DNS, and NAT function. It's important that its LAN address is different
from the LAN address of the hotspot (which you will know if you've
tested the hotspot with a WiFi-enabled laptop or similar).

Hope this helps ...


--
Graham J

[Graham J]

Patrick wrote:
> Desktop PC to Android Mobile Hotspot - What do you use for the Gateway?
> 1. My Windows 10 desktop has no Wi-Fi card.
> 2. So I Ethernet out to an old router acting as a wireless client bridge.

I'm confused by the terminology. I would expect "wireless client" to be
sufficient.

> 3. This has been working for many years.

OK so what is the internet router it normally connects to? And what LAN
IP address does it have?

> For whatever reason, the Internet went out.

To avoid confusion, power off this router while the internet is dead.

> So I set up the phone as a
> Mobile Hotspot which works for the laptop.

What LAN IP address does this laptop report when connected to the hotspot?

> But I wanted the desktop to be connected also.
> 1. So I figured I'd set up the bridge, temporarily to the Mobile Hotspot.
> 2. The Mobile Hotspot has an SSID with the same passphrase as all my APs.

I think this is very confusing. I think you should change its SSID to
be obviously different - "Hotspot" - and specify a different passphrase.

Then change the old router's wireless credentials to the values required
for the hotspot.

[snip]

> There's also a question in the DD-WRT wireless client bridge setup of:
> Local IP Address = 192.168.1.whatever/24
> Gateway = 192.168.1.1
> Local DNS = 192.168.1.1

The LAN IP address for the wireless client can only be used for
communication with the client itself. The DHCP service should be off,
which means that to communicate with the wireless client your computer
needs a static address of the form 192.168.1.another. The "gateway"
value is meaningless in this context.

Once you have the wireless client connected to the hotspot, reconfigure
your computer to "automatic IP addressing" then it will get its IP
address, DNS, and Gateway information directly from the hotspot.


--
Graham J

[Carlos E.R.]

On 2024-02-21 06:31, Patrick wrote:
> Desktop PC to Android Mobile Hotspot - What do you use for the Gateway?
> 1. My Windows 10 desktop has no Wi-Fi card.
> 2. So I Ethernet out to an old router acting as a wireless client bridge.
> 3. This has been working for many years.
>
> For whatever reason, the Internet went out. So I set up the phone as a
> Mobile Hotspot which works for the laptop.
> But I wanted the desktop to be connected also.
> 1. So I figured I'd set up the bridge, temporarily to the Mobile Hotspot.
> 2. The Mobile Hotspot has an SSID with the same passphrase as all my APs.
> 3. The Mobile Hotspot, by default, is set to 10 clients.
>
> So I saved the old router configuration to the AP.
> And I changed the SSID for the wireless client bridge to connect to.
> Since the passphrase is the same, only the SSID needed to be changed.

On most software, changing the SSID erases/reset the passphrase.

>
> Or so I had thought.
> Booted many times but the router (as a wireless client bridge) won't
> connect to the mobile phone (set up as a mobile hotspot).
>
> Why not?

Read its log and find out.

...

--
Cheers, Carlos.

[Java Jive]

On 21/02/2024 10:47, Graham J wrote:
>
> Patrick wrote:
>>
>> Desktop PC to Android Mobile Hotspot - What do you use for the Gateway?
>> 1. My Windows 10 desktop has no Wi-Fi card.
>> 2. So I Ethernet out to an old router acting as a wireless client bridge.
>
> I'm confused by the terminology.  I would expect "wireless client" to be
> sufficient.

He states that he's using a DD-WRT build, presumably it's on this
router, in which case, in DD-WRT speak, there is a difference between
the two. IIRC there are two possible settings to achieve what he wants,
one of which, a client-bridge, simply behaves as a replacement for a
piece of cabling, in that the router locks on to the source WiFi and
passes all DHCP & DNS etc straight through to its cabled LAN ports, and
does not act as an access-point. IIRC still, there is another choice
where the router does all the above but also acts like an AP in allowing
clients to its own WiFi also to make connections back to the source router.

>> 3. This has been working for many years.
>
> OK so what is the internet router it normally connects to?  And what LAN
> IP address does it have?
>
>> For whatever reason, the Internet went out.
>
> To avoid confusion, power off this router while the internet is dead.
>
>> So I set up the phone as a Mobile Hotspot which works for the laptop.
>
> What LAN IP address does this laptop report when connected to the hotspot?
>
>> But I wanted the desktop to be connected also.
>> 1. So I figured I'd set up the bridge, temporarily to the Mobile Hotspot.
>> 2. The Mobile Hotspot has an SSID with the same passphrase as all my APs.
>
> I think this is very confusing.  I think you should change its SSID to
> be obviously different - "Hotspot" - and specify a different passphrase.
>
> Then change the old router's wireless credentials to the values required
> for the hotspot.
>
> [snip]
>
>> There's also a question in the DD-WRT wireless client bridge setup of:
>> Local IP Address = 192.168.1.whatever/24
>> Gateway = 192.168.1.1
>> Local DNS = 192.168.1.1

If it's of any help, on my DD-WRT Client-Bridge, an old Cisco LinkSys
WRT320N which links my bedroom to the rest of my home LAN, the settings are:

Setup, Basic Setup, Router IP:
Local IP Address: 192.168.x.y where y is not 1
Subnet Mask: 255.255.255.0
Gateway: 192.168.x.1
Local DNS: 192.168.x.1

However, if I was trying to connect it to my tablet acting as a mobile
hotspot, I'd expect to be using a different x than that required to
connect to my primary main router. What x should be in this case you
should be able to find out either from the phone itself or if not there
then the laptop that connects successfully - on the latter start a
Command Prompt with Administrator privileges, type ...
IPConfig /all
... and note what is x for the wireless connection.

Going back to the client-bridge, Wireless, Basic Settings:
Wireless Mode: Client Bridge
Wireless Network Mode: N-Only (2.4GHz)
Wireless Network SSID: XYZ
Sensitivity Range (ACK timing): 2000 (IIRC the default)
Network Configuration: Bridged

> The LAN IP address for the wireless client can only be used for
> communication with the client itself.   The DHCP service should be off,
> which means that to communicate with the wireless client your computer
> needs a static address of the form 192.168.1.another.  The "gateway"
> value is meaningless in this context.

No, either this is incorrect or I'm misunderstanding what you're saying
because of the potential for ambiguity, so let me try a different and
hopefully entirely unambiguous explanation, (deep breath) here goes:

The client-bridge setting in the secondary DD-WRT router essentially
makes its wireless connection back to the main router behave like a
physical cable connecting the main router to its own switch and its LAN
ports beyond. As long as the desktop PC was previously set to accept a
DHCP IP & DNS from the main router, nothing should need to change;
however, if it was using a fixed IP, then obviously that would need to
change because x in the settings above is now going to be different. As
you state, I would recommend using DHCP for any devices beyond a
client-bridge, and if it was desirable that one of them has a fixed IP,
then fix that in the addresses doled out by the main router.

I have both a Network Media Player and occasionally an old laptop wired
to the bedroom client-bridge, both are set to use DHCP, but in the main
router the NMP is always given the same IP address reserved high in the
allocatable range, while the laptop just gets whatever it is given.
(You may wonder, why not use the laptop's WiFi directly? It's only G,
whereas the client-bridge is N, so the connection is significantly
faster via the client-bridge.)

--

Fake news kills!

I may be contacted via the contact address given on my website:
www.macfh.co.uk

[Andy Burns]

Patrick wrote:

> Desktop PC to Android Mobile Hotspot - What do you use for the Gateway?

Short answer: leave the desktop using DHCP and it'll Just Work™️

[Andy Burns]

Maybe your intervening router needs a DHCP helper?

[Patrick]

I do not understand your suggestion.

The desktop has a static IP address (but it could have been assigned by the
gateway for all that it matters). Coming out of the desktop is Ethernet.

The Ethernet goes into the DD-WRT wireless client bridge which DD-WRT calls
a "Repeater Bridge", the other of the 6 choices being "AP", "Station",
"Station Bridge", "Repeater" & "Ad Hoc" for the "Radio Mode".

There is no obvious setting in the DD-WRT "Repeater Bridge" setup that has
anything to do with DHCP, perhaps because bridges operate at the level of
the MAC address, and as such, are simply pass-through for IP addresses.

The router is bridged wirelessly to an access point which itself is wired
via a switch into the main router which itself connects to the modem.

The strange thing is this has been working for years, so I don't think
there is anything wrong with the DD-WRT setup. But I do wonder what
"gateway" the phone uses since the gateway of 192.168.1.1 wouldn't exist on
the phone's network when used as an access point mobile hotspot.

I looked up the term "DHCP Helper" which is indeed a thing.
https://www.freeccnaworkbook.com/workbooks/ccna/configuring-an-ip-dhcp-helper-address
"DHCP IP Helper addresses are IP addresses configured on a routed interface
such as a VLAN Interface or a routers Ethernet interface that allows that
specific device to act as a middle man which forwards BOOTP (Broadcast)
DHCP request it receives on an interface to the DHCP server specified by
the IP Helper address via unicast."

I guess I have to learn how to use "ip helpers" on DD-WRT.
https://forum.dd-wrt.com/phpBB2/viewtopic.php?p=1048324&sid=b2410a040668896d5aa3536c3b4a387c

[Patrick]

On Wed, 21 Feb 2024 13:40:06 +0000, Java Jive wrote:
> As long as the desktop PC was previously set to accept a
> DHCP IP & DNS from the main router, nothing should need to change;
> however, if it was using a fixed IP, then obviously that would need to
> change because x in the settings above is now going to be different.

Maybe the problem is the PC has a static IP address, but I don't see
anywhere in the DD-WRT setup as a "Repeater Bridge" where it cares.

The PC's IP address, as far as I can figure out, is set on the PC.
The DD-WRT "Repeater Bridge" doesn't seem to care what IP address it is.

But you are correct that it is in the same subnet as the DD-WRT "Repeater
Bridge" (and the same subnet of the AP that the DD-WRT "Repeater Bridge" is
wirelessly bridged to. Likewise that AP that the DD-WRT "Repeater Bridge"
is bridged to is wired to a switch which is wired to the main router which
is wired to the modem - all of which are on the same subnet.

I guess what you're suggesting I think about is that the phone, when put in
hotspot mode, is on a DIFFERENT subnet - which I'm sure it is.

I am looking at the suggestion from Andy about DNSmasq to maybe fix that.
https://wiki.dd-wrt.com/wiki/index.php/DNSMasq_as_DHCP_server