RUT955 Failover / DNS Woe

NETWORKING SOLUTIONS
1

Noticed this issue during today’s Starlink outage. Despite the WAN interface (plugged into a Starlink in passthrough mode) being marked as Offline, DNS queries were still being forwarded to the Starlink device. Which of course didn’t work because the Starlink outage.

When I tried setting custom DNS servers across all three interfaces (WAN, and both LTE), every DNS query would fail.

2

Hello,

You can see the DNS servers used with the following command:

cat /tmp/resolv.conf.d/resolv.conf.auto

When a DNS server is added, a new list is generated.

If the interface on which you configured the DNS server is down, this DNS server will not be in that list of DNS servers. Now, when you do an initial lookup, DNSMasq send a DNS query to all servers in the list, and resolve is based on whichever server responds first. Generally, based on the domain, many of the requests will be sent to the most reliable server, but the other servers can also be used. Thus, could you please try adding a DNS server to the LAN network as well to see if it helps?

Kind Regards,

4

Should ALL interfaces have DNS servers configured? @AndzejJ

What DNS server is used by the router itself, for example to look up rms.teltonika-networks.com ?

5

Hello,

This depends on what you are trying to achieve. Since LAN is always UP, specifying DNS servers on the LAN interface will basically mean that this DNS servers can always be used. When resolving rms.teltonika-networks.com, your normal DNS servers are used, i.e the ones in /tmp/resolv.conf.d/resolv.conf/auto. If none of the DNS servers can resolve rms.teltonika-networks.com, you will get an error that states ‘unable to resolve hostname’ or something similar, and you will not be able to connect to RMS. Usually, DNS servers are obtained from the operator if SIM card is used, and can also be seen in the list. When wired WAN is used, DNS servers are usually obtained via DHCP.

Kind Regards,

6

Ah ok. Thank you. Maybe that partly explains the issues I sometimes have with RMS connections failing (VIP ticket #291677). I checked /tmp/resolv.conf.d/resolv.conf.auto and found some ISP DNS servers listed there (I guess from DHCP). These can be unreliable. I changed them to 8.8.8.8/8.8.4.4 and will continue to do that for all interfaces. So now resolv.conf.auto looks like this:

# Interface wan
nameserver 8.8.8.8
nameserver 8.8.4.4
# Interface mob1s1a1
nameserver 8.8.8.8
nameserver 8.8.4.4
# Interface mob1s1a1_4
# Interface lan
nameserver 8.8.8.8
nameserver 8.8.4.4

I note the mob1s1a1_4 virtual interface does not get any DNS config, I assume it uses the parent.

7

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