DHCP hostname cannot be queried outside of LAN in dual-router home network setup?

[cyberal]

Hello everyone,

I am having trouble achieving my goal of a dual-router setup in my home network, where I'm able to resolve the IP address of a host while connected to the other router.
To make this more explicit:

[ISP] ==> [MODEM] ==> (WAN) [AC68U] (LAN) ==> (WAN) [AX88U] (LAN) ==> (ETH1)[PC]

Router AC68U
WAN:
Connection Type: Automatica IP
Enable WAN: Yes
Enable NAT: Yes
Enable UPnP: Yes
Enable secure UPnP: Yes
DNS:
- Connect to DNS Server Automatically: Yes
- Forward local domain queries to upstream: No
- Enable DNS Rebind: No
- Enable DNSSec: No
- DNS Privacy: None
LAN:
- Device name: asus-ac68u
- IP Address: 10.0.0.1
- Subnet Mask: 255.255.0.0
DHCP:
- Enabled: Yes
- Hide DHCP/RA queries: No
- Domain Name: foo.bar
- Default gateway: (empty)
DNS:
- DNS Server 1: (empty)
- DNS Server 2: (empty)
- Advertise router's IP: Yes
Manual assignment:
- Enabled: yes
Host (reservation):
- ASUS AX88U 10.0.0.2 asus-ax88u
LAN Route:
Enabled: Yes
- 10.1.0.0 / 255.255.0.0 / 10.0.0.2 / / LAN

Router AX68U
WAN:
WAN: Automatic/default settings
Enable WAN: Yes
Enable NAT: Yes
Nat Type: Symmetric
UPnP: Yes
Secure UPnP: Yes
WAN DNS:
Connect to DNS Server automatically: Yes
Forward local domain queries to upstream: Yes
Enable DNS Rebind protection: No
Enable DNSSec: No
Client auto DoH: Auto
DNS Privacy: None
LAN:
Host Name: asus-ax88u
Domain name: foo.bar
IP Address: 10.1.0.1
Subnet Mask: 255.255.0.0
DHCP:
- Enabled: Yes
- Hide DHCP/RA queries: No
- Domain name: foo.bar
- Default gateway: (empty)
DNS:
-Server 1: (empty)
-Server 2: (empty)
- Advertise router's IP in addition to user-specified DNS: Yes
Manual assignment:
- Enabled: yes
Host (reservation):
- PC NAME 10.1.1.5 pc-name

I can confirm that routing by IP works regardless of which router I'm connected to (i'm connecting via WiFi to be specific):
ping 10.1.1.5

Resolving by hostname works correctly if I'm connected to AX88's LAN network. All of the following work:
dig pc-name.foo.bar
dig pc-name
dig @10.1.0.1 pc-name.foo.bar
dig @10.1.0.1 pc-name

but resolving by hostname if I'm connected to the AC68U's LAN network, won't work at all.
The commands that I believe should work are:
dig @10.1.0.1 pc-name.foo.bar (which uses the LAN IP of AX88U)
dig @10.0.0.2 pc-name.foo.bar (using the WAN IP of AX88U)

What am I doing wrong? I need to be able to have a device in AC68U's LAN that communicates to the devices in AX88U's LAN using hostname instead of IPs directly. Is there another way to achieve this?

Thanks!

 

[ColinTaylor]

This is not a valid network design. You have two separate networks, 10.0.x.x and 10.1.x.x. Each network is running its own DNS server, but each server thinks that its network is foo.bar. You can't shouldn't have two different networks owning the same domain name.

It would be much simpler to reconfigure the second router as an access point and thereby create a single network (10.0.x.x).

 

[drewski22785]

@ColinTaylor is correct this isn't valid and AP mode would definitely solve your issue. The key question, is there a reason ap mode doesnt work for you? I ask because I had what I considered valid reason and there is some scripting you can do to work around this. But as I write this I am trying to find a way to make AP mode work with my needs so that is definitely the preferred method!

 

[cyberal]

I'm okay changing the domain of the AX88U to something else like "baz" if that allows me to resolve the host pc-name.baz while connected to the AX68U router but my gut feeling is that this isn't enough.

Regarding using the AX88U as access point, I'm refraining from that approach (perhaps based on bad assumptions) because:
1. i need to connect wired clients to this device (APs are only for WiFi right?)
2. I need to connect an external hard drive to be exposed to the network. I can't connect this HDD to the AC68U because of space constraints on the tiny closet where it lives. Can APs have USB devices connected?
3. I would like to more generally delegate as much workload to the AX88U instead to benefit from it being a more powerful router (eg. Configure it under DMZ and use VPN features both inside and outside the network, JFFS scripts, etc.
4. I plan on using a 4G modem as backup in case the isp goes down but i can only connect it to the AX88U because the AC's location has really bad reception

To be honest if i could, i would drop the AC68U from my network altogether, but i just can't because besides being used to connect the AX i also have a couple other wired devices connected here that i can't connect to the AX without having to lay new wire around my home (which i can't do since it's a rental). If i were to position the AX in the cabinet where the AC is, i would not be able to cover the area i need to cover with Wifi either

 

[cyberal]

Forgot to finish my previous post asking if there's another network design that would be valid that would allow me to share the same ISP connection and have wired and wireless devices on both LANs be able to communicate with each other? So i just need to use a whole different private network address in the AX88U (say 192.168.X.X) and do static routing with that? If the issue is two DNS servers, how can I turn off one DHCP server and have the clients find their IPs regardless of which router they are connected to?

Any suggestions are welcome

 

[ColinTaylor]

1. Wired devices can be connected to the access point.
2. Yes you can attach USB devices to an access point.
3. VPN options are unavailable in AP mode.
4. Dual WAN is a routing function and therefore also unavailable in AP mode. However if the AX88U were to fail-over to 4G you would loose all connectivity to the AC68U network.

The problems aren't just DNS, that's just the starting point. You also have routing and NAT/firewall issues that need to be addressed.

So some background questions -

Can you swap the routers around so that the AX88U is connected to the internet?
Are you talking about a VPN server or client or both? Are these in use all the time?
How important is it that all devices on each network have complete access to each other?
Do you really need to resolve local DNS names for the "other" network? Could you just use IP addresses (when accessing AX88U devices from the AC68U network) instead?
4G fail-over: As above, in fail-over mode the other network is unreachable. Is this acceptable?

The primary problems are likely to be around your use case of 4G fail-over and VPN.