How to set up alternate LAN access using hotspot

mfoley · 03-01-2021, 01:06 PM

Occasionally my Internet provider, Spectrum, drop out for an annoyingly long period, usually when I'm in the middle of writing a program remotely. I have the following configuration:

host "quadmon" - local Slackware-Current computer used for human interaction. IP 192.168.0.17

host "server" - local Linux file server and email server. IP 192.168.0.15

router: Asus RT-AC66U B1 configured as the gateway and name server. IP 192.168.0.1

When I lose Internet connection I want to be able to connect using my smart phone hot spot. That's easy enough on "quadmon" as I have a wireless dongle plugged in there and it connects just fine. I can connect to the Internet from there. It's IP is then (e.g.) 192.168.43.66 and 'route' gives:

Code:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.43.1    0.0.0.0         UG    303    0        0 wlan0
loopback        0.0.0.0         255.0.0.0       U     0      0        0 lo
192.168.0.0     0.0.0.0         255.255.255.0   U     0      0        0 eth0
192.168.43.0    0.0.0.0         255.255.255.0   U     303    0        0 wlan0

If I modify quadmon's inet1.conf to hard-code the eth0 interface to 192.168.0.17 (normally, it is DHCP="yes"), I can then connect to "server" at 192.168.0.15 (wired).

My problem is that "server" cannot connect to the Internet since it is wired and relying on the now disconnected ASUS router for everything. I'd like to configure "quadmon" as the router/gateway. I've tried the following:

On "quadmon" /proc/sys/net/ipv4/ip_forward = 1. inet1.conf is:

Code:

IPADDR[0]="192.168.0.17"
NETMASK[0]="255.255.255.0"
IPALIASES[0]=""
USE_DHCP[0]="no"

IFNAME[4]="wlan0"
USE_DHCP[4]="yes"
WLAN_WPA[4]="wpa_supplicant"

and iptables has:

Code:

iptables --table nat --append POSTROUTING --out-interface wlan0 -j MASQUERADE
iptables --append FORWARD --in-interface eth0 -j ACCEPT

On "server", I changed the inet1.conf to:

Code:

IPADDR[0]="192.168.0.15"
NETMASK[0]="255.255.255.0"
USE_DHCP[0]="no"

# The following is the IP of "quadmon"
GATEWAY="192.168.43.66"

I change /etc/resolv.conf to:

Code:

nameserver 192.168.43.66

But, it's not working. "server" still can't get out (resolve external domain names) or resolve local host names.

What am I missing?

mralk3 · 03-01-2021, 09:18 PM

Maybe I've misread, but I have a few suggestions.

You need to make sure your /etc/resolv.conf is reflecting the dns settings of your hotspot and also glance over /etc/hosts. You can also save yourself some trouble and use the hostapd SlackBuild. It will let you easily configure a hotspot. After that you can add dnsmasq for DNS if you value DNSSEC or other protections. DHCPCD is overkill for this, so also configure dnsmasq to serve dhcp. If you do not want to bother with dnsmasq, then set your interfaces to static IP addresses (as you've done). As far as I know, wpa_supplicant is just used to set up client machines.

https://slackbuilds.org/repository/1...search=hostapd

There are some security advisories for hostapd listed here: https://w1.fi/security/2021-1/ and here: https://w1.fi/security/2020-2/ Just drop the patches as is into the "patches" directory of the SlackBuild. Or just use it as is. I run my home gateway wireless access point 24x7 for the last 4 years with hostapd.

baumei · 03-01-2021, 10:30 PM

I suggest getting a 'wireless client to ethernet' adapter. Configure this adapter to connect wirelessly to the hotspot on your telephone, and plug the ethernet cable from the adapter to the WAN port of your ASUS router.

If the ASUS router provides ALL the domain name resolution for the LAN, then everything should be working --- however, if the hosts on the LAN are configured to use the Spectrum DNS servers, then while the LAN is connected to the hotspot those Spectrum DNS entries will probably need to be removed from the /etc/resolv.conf file of the hosts.