DNS question

[bigegg]

I'm currently setting up a "smart home" system using home assistant.

I have "adguard" running which I use to resolve IP addresses from .local URLs - mainly so I can get into the webservers of connected devices.

I have static IPs set up in my router for the various things so I simply add a line in the adguard config: (eg) "HomeAssistant.local : 192.168.1.35" so I type "homeassistant.local" in my browser, and it opens the webserver page for 192.168.1.35

I've run into a bit of a problem, though: I need a way to resolve the URL to an "alternate" IP if the first is unavailable for a couple of devices...


TLDR:
is there a way to resolve a URL to a list of hosts, in order, depending upon which is available?

I'm sure it must be an obvious feature, but as you may guess, I don't know the terminology to Google an answer...

 

[frank horton]

I want less not more of this stuff.....hahaha....sorry

 

[Kayos]

I want less not more of this stuff.....hahaha....sorry

Its progress

Crt screens and dialup were great in their day, id put money on that NOT being how you made your last reply

 

[droopsnoot]

It's a while since I've done this. As I recall it, it's not really a DNS thing as DNS is over and done with by the time you actually try to connect to the server - all it does is translate the name into an IP address. You're probably looking for some kind of "failover" support.

Some of it's used for load balancing, so if you had three terminal servers and wanted to connect to terminalserver.local, the load balancer would pick one based on current load, or a simpler version would be a "round-robin" style where you define your three terminal servers, connect to the presented address and the server would just send each new request to the "next" server, and loop round when it reaches the end of the list. But I think that's something at the next level along from the DNS.

 

[MetalMonkey]

I'm not familiar with adguard but I think you are asking more of an adguard configuration question rather than a DNS question.
There are a couple of ways for DNS to resolve a name to multiple IP's - Failover and Round Robin. However I don't think either are suitable in your situation, as it appears you are just doing a local resolve.

What you perhaps could do is write a monitoring script which runs in the background pinging the IP addresses and rewrites the adguard configuration file (and presumably restarts the service) if it detects an IP is down for x amount of time.
Alternatively you could try adding an alias to your hosts file and see if that works.

 

[Fastdruid]

Short answer is "no".

You can have round-robin DNS or point it towards a load balancer but DNS itself doesn't care if the IP itself is accessible.

EDIT: I've just realised your using a .local domain name. The .local suffix is reserved for Multicast DNS (or mDNS)[1] which doesn't use a name server for resolution. If you've got anything that is linux based that uses systemd the default is to use mDNS and it will cause all sorts of problems if you're expecting it to perform proper lookups. Curse MS for making it the "default" for AD domains and hence re-used by people when it shouldn't be.

That said, some load balancers are little more than a "healthcheck" script that updates DNS on the fly, you could do similar with a regularly running script and a caching DNS server that is authoritative for the domain. Just update the records (with a suitably low TTL) depending on availability. You may need to not use a .local though or mess with systemd to not treat .local as mDNS.

[1] https://stevessmarthomeguide.com/multicast-dns

 

[Stueeee]

It been a long time now since I worked on this stuff, but critical network appliances were set so that a standby device would assume the IP address and the MAC address of the main device when there was a connectivity issue at the main device. The MAC address change is necessary because of the persistence of IP to MAC address mappings in the ARP tables of all the other devices on the subnet. Not sure if this kind of stuff is available on servers nowadays.

 

[Fastdruid]

It been a long time now since I worked on this stuff, but critical network appliances were set so that a standby device would assume the IP address and the MAC address of the main device when there was a connectivity issue at the main device. The MAC address change is necessary because of the persistence of IP to MAC address mappings in the ARP tables of all the other devices on the subnet. Not sure if this kind of stuff is available on servers nowadays.

HA clusters like that have been around on servers for many, many years. Issue is that the clustering then is handled by the "server" and that's typically not possible on "home" devices which often have a cut down version of linux and you can't install extra software. Without the ability to do that you'd need a load-balancer on the front end.

 

[brewdexta]

As DNS is not stateful, you will need a means of failing over between servers using the same IP. You could use a virtual IP and something like VRRP however this would only protect you from a network issue, i.e. if a server died completely or other network influencing issues. You can link a virtual IP with application state, typically that is done with a load balancer, there are open source load balancers out there. The load balancer regularly tests the servers for state, if its a web server then it could be as simple as a http 200 "server ok" reply. If it doesn't get an answer or something like a http 5xx server error message then it would take that server out of the list of available servers. You can also use Dynamic Global load balancing features where the faulty server's DNS entry is dynamically removed if unavailable, but you can get into DNS cache issues so not instant. There's loads of other ways to do this but the above are the most common simple approaches.

 

[bigegg]

The issue I have is that I have two WiFi repeaters: the devices sometimes connect to one of the repeaters, sometimes to the other.
Each repeater assigns a different MAC address to the device (as far as the router is concerned), so the router considers them different devices - and therefore won't reserve the same IP address for the two MACs.

I was hoping I could just add a line of code to the DNS config file to sort it.

Unfortunately, the device doesn't allow for requesting a static IP: it has to be done via DHCP.

I think I will have to go down the route of only allowing the device to connect to one or the other WIFI extenders (so they would always have the same MAC address) - and cope with a potentially worse connection.
(Not necessarily a problem for these devices).

 

[carbon]

Each repeater assigns a different MAC address to the device

The mac address shouldn't change but the ip address can. It may be possible to bind the device to a specific ip on your router. I have HA running here and have two additional access points. The router and both access points all report the exact same mac address for any one of the devices.

 

[Fastdruid]

If you're getting a different MAC each time are they using the WiFi security feature that randomises it? Can you change the setting to disable that?

 

[carbon]

Have you got DHCP disabled on the access points?

 

[bigegg]

The WiFi repeater *definitely* assigns a different (static) *MAC* address to each device.

The MAC addresses starting "AE : 84 : C6" are devices connected via the extender.

 

[MetalMonkey]

The MAC address is determined by the device and is usually assigned when it is manufactured, a router or wifi repeater can't assign a device a MAC address.
Something else is going on.

Static IP addresses aren't requested either - a static IP is one you set on the device so it is always the same. You then have to ensure that those addresss are excluded from the range of DHCP addresses that your router might hand out to avoid potential clashes.
You can set reserved IP addresses which are based on MAC, these aren't static they are still DHCP, it just means the same one is handed out to the same device each time.

 

[bigegg]

The MAC address is determined by the device and is usually assigned when it is manufactured, a router or wifi repeater can't assign a device a MAC address.
Something else is going on.

Static IP addresses aren't requested either - a static IP is one you set on the device so it is always the same. You then have to ensure that those addresss are excluded from the range of DHCP addresses that your router might hand out to avoid potential clashes.
You can set reserved IP addresses which are based on MAC, these aren't static they are still DHCP, it just means the same one is handed out to the same device each time.

I said I didn't know the terminology.

The "MAC address" is *definitely* assigned by the repeater.
(It's a TP LINK re360, if you are interested)

I "reserve" IP addresses for each device - based on one of the two MAC addresses which it appears to be - but I want to be able to point (say) "HomeAssistant.server" (or "boiler.server", or "kitchen.server" or whatever) to whichever (of the two reserved) IP address has been assigned by the router DHCP service.

I was under the impression that a device connecting to a network could request an IP address, rather having a random one assigned by DHCP?

 

[carbon]

I was under the impression that a device connecting to a network could request an IP address, rather having a random one assigned by DHCP?

Yes, I can either set a static ip on a device like a d1 mini or I can bind a specific mac to a static IP address. It depends on what router you have

I’ve never used a supplied router from an isp but have used ones that have given me more control over devices

 

[MetalMonkey]

I said I didn't know the terminology.

The "MAC address" is *definitely* assigned by the repeater.
(It's a TP LINK re360, if you are interested)

I "reserve" IP addresses for each device - based on one of the two MAC addresses which it appears to be - but I want to be able to point (say) "HomeAssistant.server" (or "boiler.server", or "kitchen.server" or whatever) to whichever (of the two reserved) IP address has been assigned by the router DHCP service.

I was under the impression that a device connecting to a network could request an IP address, rather having a random one assigned by DHCP?

Its not a problem, I was just trying to clarify the different terms and what they mean.
Again, not to be pedantic, but the MAC cannot be assigned by the repeater - so I'd start from that premise as it might be a clue to work out what is going on.

I wonder if what you might be seeing as the reported MAC for the device by the repeater might not be the actual MAC of the device, and that might be why your reservations aren't working.
For example I note that you have a pixel3 with an 8A mac address - which looks to me like it has MAC randomising turned on - If you change it on the phone to "Use device MAC" instead then you should get the same MAC address showing each time you connect.

The way the DHCP works, (very basically) is the device connects to the network and asks if their are any DHCP servers.
The DHCP server(s) will then respond and offer an IP address to the device.
The device then can choose to accept the IP address and if it does it will send an acknowledgement so the server knows that DHCP lease has been taken.

The client doesn't request a specific IP - the way reserved IP addresses work is that you tell the DHCP server that you want a specific device (identified by the MAC address) to have a specific IP address.
When a device with that MAC address connects to the network and asks the server for a lease, the server assigns it the reserverd IP address because the MAC address matches the one it has in its list.

I'd say step one is use your 'phone to debug what is going on - make sure it has device MAC turned on, note down what the phone says it is, and then check your repeaters/router and see if it matches.

 

[carbon]

Have you turned off DHCP on your repeaters? You only need DHCP enabled on your router if everything has the same ssid and password

 

[bigegg]

Have you turned off DHCP on your repeaters? You only need DHCP enabled on your router if everything has the same ssid and password

The repeater doesn't have DHCP, as far as I can see.