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9
Help! DNS A Records only ones getting filtered. (lemmy.world)
submitted 8 hours ago by [email protected] to c/[email protected]
8 comments fedilink hide all child comments
 

I’m pulling my hair out over this. I’ve got a proxmox homelab, an LXC running technitium installed from TTeck’s script.

The DNS server is also doing DHCP for my network. I have an authoritative zone for ‘.lan’

I can get NS, SOA, TXT records from the DNS server, but no A records! The DNS query logs show that it gives an answer, and if I am on the DNS server itself I get an answer, but no other machines on the network hear the reply.

I think this means the DNS server is working properly. There are no FWs in the way as I can resolve other types.

Where else can I look, or how can I diagnose this? I am completely at a loss.

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[–] [email protected] 6 points 5 hours ago* (last edited 5 hours ago) (1 children)

Here is how I would diagnose (I'm assuming you have Linux / WSL on a client)

  1. Check the DNS record is actually set (yes do it again)
  2. Do these steps on the client:
  3. dig $domain check which server answered
  4. dig a $domain should give a record
  5. dig a $domain @server to make sure you're querying the right server

If none work, probably network issue (DNS boind to wrong IP, firewall, etc)

If 3 and 5 work but 4 doesn't, your DNS isn't authorative.

If only 5 works DNS settings on the client is wrong.

[–] [email protected] 2 points 4 hours ago (1 children)

Thanks for giving it some thought!

I have been testing using dig @192.168.0.249 study.lan

3, 4, and 5 work for TXT, NS and SOA but doesn’t work for A records. I think this rules out a simple network issue?

[–] [email protected] 1 points 6 minutes ago

Just to be sure you do dig A @server $domain (with the "A") and can confirm the following

SERVER is your server

;; ANSWER SECTION is empty (or doesn't exist)

;; AUTHORITY SECTION mentions your local DNS server

Also check

dig NS @server $domain

Is your server in the answer section?

[–] [email protected] 1 points 5 hours ago (1 children)

How exactly are you testing this from your client, with ping? What are you using to query the DNS?

If you run nslookup from the client

  • Does the ‘server’ command return the correct DNS server?
  • Does .lan return the expected record?

I’m assuming you’ve run ifconfig to verify your client’s NIC has been assigned the correct DNS via DHCP?

[–] [email protected] 1 points 4 hours ago

Thanks for replying, I appreciate the response.

I’m running dig @192.168.0.249 study.lan from my client (a MacBook).

If I run ‘dig @192.168.0.249 study.lan TXT’ I get a correct response (I have added a txt record)

If I run ‘dig @192.168.0.249 lan SOA’ or ‘NS’ I correctly get the records for the zone.

I think this eliminates the possibility of it being a routing error?

[–] [email protected] 2 points 6 hours ago (1 children)

Run Wireshark on the client to see if you actually got the reply.

[–] [email protected] 1 points 4 hours ago (1 children)

Thanks for the suggestion, I’ll grab a cap to check.

I’m running tcpdump -i any port 53. I can see the outbound request but not the reply. Will the cap show me anything more?

[–] [email protected] 1 points 3 minutes ago

Do tcpdump host $server instead. Otherwise you will only see the request (the response goes to a different port).