Local DNS not updating after wan IP change and DDNS

Installing and Using OpenWrt
1

I have a custom DDNS that I use on several routers that works fine. On one router though, when the IP changes (happens every reboot of the router) the DNS host record is changed, I can use another machine outside the LAN and the change is seen, but if I log onto the router or any machine on the LAN and ping the DDNS domain, it is still the old IP.

I have found that if I modify the DNS server IP for the WAN interface and apply changes, regardless of what the new DNS server is, when I then ping the hostname it is the right IP.

Is there a way to refresh local DNS on the router? I tried just restarting dnsmasq but that doesn't work.

2

It should update when TTL expired and next query is made.

If this isn't working, you nay need to adjust TTL.

2 Likes
3

So I'm not sure where I'm going to change TTL. Can you tell me where that would be?

4

This would be set at the hosting company that handles of your domain name (i.e. DNS Server). For DDNS (and other purposes), it's commonly set to 300 seconds.

5

Ahh... Ok, so, as I pointed out, from outside of my local network I can access the router via the ddns hostname so the problem is only the LAN side. It seems to be DNS caching, but restarting dnsmasq doesn't resolve it..

1 Like
6

There are multiple possible DNS caches: browser, localhost, router, upstream gateway, ISP.
Some of those may involve DNS hijacking, which you can bypass with VPN or DNS encryption.

1 Like
7

This is specifically on the router. If I do a ping hostname.ddnsserver.com from ssh on the router, it's the wrong ip.

8
  • Is it always the same wrong IP - or different ones?
  • And is this IP Public or Private?
9

How did you restart dnsmasq?

From https://thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html#lbAG:

When it receives a SIGHUP, dnsmasq clears its cache and then re-loads /etc/hosts and /etc/ethers and any file given by --dhcp-hostsfile, --dhcp-hostsdir, --dhcp-optsfile, --dhcp-optsdir, --addn-hosts or --hostsdir. The DHCP lease change script is called for all existing DHCP leases. If --no-poll is set SIGHUP also re-reads /etc/resolv.conf. SIGHUP does NOT re-read the configuration file.

10

Stays the same as before boot. Public IP

11

What is the correct cli way to restart dnsmasq so it will clear cache?

12

killall -HUP dnsmasq

13

That didn't make any difference. So to summarize:

I reboot and the router comes up with a new IP:

#1 - Ddns is working. I can immediately go on my phone using GSM, I can connect to the router on the new IP.

#2 - On the router, the IP4 upstream IP is correct.

#3 - SSH into the router and nslookup shows the old IP address still.

root@router:~# nslookup home.xxxxxxxxx.xxx

Server: 127.0.0.1
Address: 127.0.0.1:53

Non-authoritative answer:
Name: home.xxxxxxxxx.xxx
Address: xxx.xxx.xxx.xxx <- old address
Non-authoritative answer:

#4
killall -HUP dnsmasq
nslookup is still the same old address.

14

This indicates the cause of the issue is related to your upstream DNS provider.