AC86U - Odd DNS info

[Patrick9876]

I'm running Merlin 384.14_2 on an AC86U. Occasionally the host name/IP addr association of a computer, as reported by the DNS, gets corrupted and I'm not sure where to start in debugging this. The computer gets its IP addr from the DHCP server on the router. It has always gotten 192.168.1.81. And usually an NSLOOKUP for the computer's host name return 192.168.1.81. But occasionally the DNS server returns 192.168.1.94. And once, an IPv6 query returned 192.168.94 while an IPv4 query returned 192.168.1.81. (The difference may have been the result of a cached reply so I'll ignore that one occurrence for now.) The computer's IP address always stays 192.168.1.81 and can (almost) always be accessed by IP addr even when the DNS server if is wrong.

The "almost" in that last sentence is a slight hedge. Yesterday I briefly lost communication with the computer. When I tried reestablishing the connection I had to use the IP addr; the DNS info had changed. If this had been just a problem in the DNS server, the connection would not have broken so I assume the computer did something to initiate this condition. (It could be caused by something in the router, but nothing else was obviously disrupted, and the problem present itself only twith this one computer.)

I have never seen any display in the router mentioning 192.168.1.94. Even when the DNS responds to a query with 192.168.1.94 the router shows this computer as 192.168.1.81 in the list of clients. And IP config displays on the computer always have shown 192.168.1.81, but I could easily have missed a transient condition where the other address is present.

Anyone have an idea of how I can find and fix the problem?

I've demonstrated before on this forum that I don't understand how DNS servers work, and have just spent half a day trying to find a description of the host / DNS server handshake where the computer registers its host name with the DNS server. I'll willingly accept an RTFM if someone will point me to the correct fine manual.

 

[L&LD]

Is there another router on this network? An AP?

Why are you not running v384.16_0 release final yet?

 

[Patrick9876]

No, there is no other router on my network. There are a couple NAS drives that have DNS server code, but I have that disabled ... as far as I know; I'd better check.

I usually give new firmware a month or two before jumping on the bandwagon. I've been even more cautious with ASUS router firmware once I read that new releases sometimes require a factory reset. Reentering the config is a pain ... especially the 24-character SSIDs I use.

 

[ColinTaylor]

What sort of computer is this? PC, laptop, tablet, etc.

Does it have more than one network interface connected, e.g. wired and wireless?

Do you have any repeaters or range extenders?

 

[Patrick9876]

It's a desktop PC. It has both an Ethernet interface and a wireless interface. The wireless interface is enabled but not connected. No repeaters or range extenders.

I suppose if the Ethernet connection briefly got broken the wireless interface might have connected and then disconnected when the Ethernet interface recovered. But wouldn't the router reflect that?

 

[ColinTaylor]

I would make sure the wireless interface is disabled and see if that fixes it.

 

[Patrick9876]

OK. I'll disable the wireless interface. (Actually, I'll unplug the wireless adapter.)

But in the meantime I tried Ethernet-connecting a laptop that usually uses wireless. Both nslookup queries and the router's client list tracked the laptop's connectivity - showing the address of the Ethernet connection when Ethernet connected (but with the wireless interface still enabled), and showing the address of the wireless interface when I disconnected the Ethernet cable.

I know that doesn't exactly match the PC's configuration since the PC's Ethernet connection made the initial contact with the router, but I doubt that matters.

 

[Patrick9876]

In spite of what I said in my last update, I haven't disabled the interface yet. I want the problem to appear one more time so I can do some more debugging,

 

[john9527]

But in the meantime I tried Ethernet-connecting a laptop that usually uses wireless. Both nslookup queries and the router's client list tracked the laptop's connectivity - showing the address of the Ethernet connection when Ethernet connected (but with the wireless interface still enabled), and showing the address of the wireless interface when I disconnected the Ethernet cable.

Laptops often have a built in function that automatically disables one interface if the other is active. Are you sure that both interfaces were really active?

What happens on a desktop is that depending on how the wireless is configured, you can try to end up with two clients with the same name, which really confuses things. If you try and connect the interfaces one at a time, does the same name show for both connections?

 

[Patrick9876]

Laptops often have a built in function that automatically disables one interface if the other is active. Are you sure that both interfaces were really active?

I don't know if both interfaces were active, but I suspect they were not.

What happens on a desktop is that depending on how the wireless is configured, you can try to end up with two clients with the same name, which really confuses things. If you try and connect the interfaces one at a time, does the same name show for both connections?

Yup. That was it. I didn't actually do what you suggested, but I disconnected the Ethernet cable and the DNS server suddenly switch the PC's IP address to 192.168.1.94 and (surprise, surprise) 192.168.1.94 was the IP addr of the wireless connection.

I still don't know why the address as reported the the DNS server suddenly would switch. but I've now got the wireless adapter unplugged so I shouldn't have the problem again.