Network configuration problem.

[Erik P. Olsen]

On Thu, 2022-07-28 at 18:31, Stewart Nelson wrote:
> Hi Erik,
> 
> > > You probably have the Linksys set up to do NAT (the default, and
> > > impossible to turn off in many models).  That will block requests from
> > > 192.168.1 to 192.168.2 .  You could possibly set it up non-NAT, but
> > > then your Internet router would need to be configured with a static
> > > route and to do NAT for the other subnet.
> 
> > No, I don't think it does NAT. How can I verify that? There is nothing
> > of this kind in the configuration dialogs.
> 
> All inexpensive routers (those intended to share a DSL or cable modem
> connection) use NAT by default.  That's because the ISP only provides
> a single public IP address to the typical residential or small business
> user.  In your present setup, you can ping from 192.168.2.125 to
> 192.168.2.1 .  While doing this, run ethereal or tcpdump on 192.168.1.1
> and look at the ICMP request packets coming in.  I'll bet that the
> source address will be 192.168.1.7, rather than 192.168.2.125, showing
> that NAT is enabled.  On many small routers, it's not possible to
> turn NAT off.  On some Linksys models, in Advanced->Routing, you
> can change the Operating Mode from Gateway to Router to disable NAT.
> But IMHO, that is not the right solution for you, because you have
> no administrative control over your Internet router, and you would
> need to change settings there, if you want to have the Linksys be
> non-NAT and still provide Internet access to the wireless clients.
> 
> > > IMO, if you don't need extra security between your customers and the
> > > office LAN, it is easiest to set up the Linksys as just an access
> > > point, not using its routing function.  To do this, disconnect the
> > > WAN port altogether.  From a PC on its LAN side, change the Linksys
> > > WAN address to something that does not conflict, e.g. 192.168.3.7 .
> 
> > But the present address, 192.168.2.1, does not conflict.
> 
> Sorry if I was not clear.  I meant to say that you should change
> it to avoid a conflict on the next step.  But I now know (from
> another message you sent) that the Linksys WAN address was supplied
> by DHCP from the Internet router, so you don't need to do anything
> but disconnect the WAN port and reboot the Linksys.
> 
> > > Then, disable its DHCP server, and change its LAN address to 192.168.1.7 .
> 
> > I can't change the DHCP server. It belongs to the ISP. They'll do the
> > change for a fee and I loose support if I do. I'll rather change ISP
> > than their router.
> 
> I meant that you should disable the Linksys DHCP server.  On my WRT54G,
> on the DHCP tab, there is a DHCP Server: entry that you can set to
> Disable.  On your model, it may be different.
> 
> > > Connect a LAN port on the Linksys to your office LAN switch.  If neither
> > > side is auto MDI/MDX, you will need a crossover cable.  Now, your
> > > wireless clients will get IP addresses 192.168.1.x, handed out by
> > > whatever does DHCP on your office LAN, presumably either the Internet
> > > router or your server.  The Linksys will just be a bridge, so you
> > > don't need any special routes on your server.
> 
> > I had a similar setup at the very beginning and it worked fine except I
> > could establish a mail server. The NAT in the WAN router translates
> > incoming SMTP traffic to 192.168.1.2 and that was never reflected to the
> > connected subnet due to addressing conflicts. I had to connect the mail
> > server to the WAN router and reconfigure the wireless router to
> > 192.168.2.0 and that's when I lost connection from the mail server to
> > the customer machines on the wireless network.
> 
> I assume that you meant to say "... could not establish a mail server" :)

Yes.

> I believe that your trouble was the conflicting DHCP servers.  Try this
> again, after disabling the Linksys DHCP server, and resetting the Linksys
> LAN address to 192.168.1.x that does not conflict with other hosts on
> your LAN, and is out of the range of addresses handed out by your Internet
> router.

I am a little confused. I want to be sure I understand precisely what
you want me to do:

1. Disable DHCP in the wireless router
2. Change the router's WAN address to 192.168.1.x. I could probably go
back to the original 192.168.1.7.
3. Define static adresses for the computers on the wireless LAN.

One question: The internet router's addressing range has 192.168.1.1
through 192.168.1.5 as fixed and reserved addresses. All the rest up to
192.168.1.254 are assigned by its DHCP. Won't that conflict with the
same addressing range in the wireless LAN if I set the address to
192.168.1.7?

> If it still doesn't work, please tell me the models of your Linksys and
> Internet routers, and what service(s) on the wireless LAN that you want
> to access from your server.

The wireless router is Linksys WRT54G and the WAN router is SpeedStream
5711.

The server should be able to ftp to the computers on the wireless LAN
and the various computers should communicate by e-mail using mail server
on the main server.

-- 
Regards,
Erik P. Olsen