Dnsmasq peculiarity (maybe?)

[Patrick9876]

RT-AC86U Merlin 384.18

Yesterday I was getting some dropped wireless connections so I rebooted my router (for the 1st time in over a month). After the reboot all powered up devices - 2 computers, 3 NAS devices, 1 thermostat on a guest network - showed in the router's client list except for 1 NAS. I had no trouble accessing the NAS by address but name resolution failed on the 2 computers. I have a CNAME records in dnsmasq.conf.add mapping 2 names to the "real" host name and resolution of all 3 names failed (according to NSLOOKUP on the computers).

I didn't want to reboot the router again so I rebooted the NAS . No logic behind that; just desperation. And it worked!

So, finally, some questions.

1. Is there some kind of DNS handshake that takes place between the router and the local devices when the router initializes? If so, what would cause the failure of DNS handshake to fail between the router and the NAS (and not between the router and other devices?
2. Is the router's client list just related to DNS of did the missing client entry indication that the router knew nothing about the NAS? And if the latter, why were the computers able to access the NAS? Had the cached ARP stuff from when the router knew about the NAS? (And if that question is stupid, try to let me know why.)
3. Could I have done something less disruptive than rebooting the NAS? Would unplugging and replugging the Ethernet cable been enough?

 

[ColinTaylor]

I have a CNAME records in dnsmasq.conf.add mapping 2 names to the "real" host name and resolution of all 3 names failed (according to NSLOOKUP on the computers).

How is your router getting the NAS's "real host name" in the first place? This sounds like your previous issue.

 

[Patrick9876]

How is your router getting the NAS's "real host name" in the first place? This sounds like your previous issue.

Well, that is sort of my real question here. As was pretty clear in that previous thread, I have no idea how the router gets the names of any the devices on the LAN. I'm sure there's an RFC describing the process but I haven't found it. All I know is that usually the router gets (and shows in the Clients list) the host names of all of the devices on the LAN.

Once I discovered I had to use fully qualified names in the CNAME record I've had no problem with the name aliasing ... as long as the router gets the real name. And I've had no trouble in the router's getting that real name until this one time.

 

[ColinTaylor]

Is your NAS's network interface configured statically or as a DHCP client?

 

[Patrick9876]

DHCP. And the NAS in question was given (or still had cached) the same address it's used for months. Accessing the NAS by address worked fine. It was just name resolution that was broken.

 

[ColinTaylor]

Is the NAS connected directly to the router by Ethernet or is there an intermediate switch?

Is the "real" host name of the NAS set in the NAS's network configuration or in the router's DHCP settings, or both?

 

[Patrick9876]

Sorry for the delay.

The NAS is directly cabled to the router - no switch or hub in between.

The NAS host name is set in NAS's network configuration. I can't swear I did not also set it in the router at some point. I set the name for some device once and could not find how to undo it so I changed the name to match the device's host name. I don't think it was this NAS, but it could have been.

 

[ColinTaylor]

Check that the real name of the NAS is set on the router at LAN - DHCP Server along with whatever IP address you want it to use.

 

[Patrick9876]

I understand what you are saying, but I don't understand why. I guess there's no reason I shouldn't use a hard-coded IP address (whether set in the DHCP server as you suggest or a static IP address), but I'm perfectly willing to accept whatever address the DHCP server gives the NAS ... as long as name resolution is working.

Name resolution for the NAS host name and aliases have been working fine for 4 months (including at least one change in the assigned IP address).

 

[ColinTaylor]

I guess there's no reason I shouldn't use a hard-coded IP address (whether set in the DHCP server as you suggest or a static IP address)...

That's my point, the host name (and therefore an IP address, although that's irrelevant for our purposes) must be set on the router not just the NAS. The reason being, as you have seen before, is that there seems to be an issue with the NAS where it doesn't always register its name with the DNS server when it should. When this happens the name resolution will fail. The solution is to either fix the errant behaviour of the NAS, or work around the problem by setting the host name on the router.

 

[Patrick9876]

Hah! Now I get it. You've suggested a circumvention to a problem. I thought you were saying this was needed in general (which didn't make sense to me). And now I know that there is a host name registration that should be happening, but isn't, when the router and NAS first contact each other - that it's up to the NAS to initiate this, rather than something the router initiates. (Maybe this should be obvious, but it's not to me.)