I’m seeing intermittent UDP loss on an RG520N-EB, firmware RG520NEBDCR03A02M4G_OCPU_02.200.00.000, running in a router (Teltonika TRB501) on a Hungarian Telekom (DT group) network, 5G NSA.
Symptoms:
- DNS lookups fail intermittently, many times per day. Probes to 1.1.1.1 and 8.8.8.8 both fail at the same moment, so it’s not a resolver-side issue.
- ICMP to the same addresses stays up throughout — no ping loss at all during these events.
- Failures last from a few seconds up to ~90 seconds.
- Video streams (QUIC/HTTP3, so UDP) stall during the same periods, while established TCP connections (SSH, long-lived sessions) stay alive.
- Nothing is logged on the router when this happens — no interface state change, no modem reconnect, no error.
What I have already ruled out:
- The router’s firewall and NAT rules — no UDP or port 53 rules exist, and all drop/reject counters are zero.
- Anything between the router and the devices behind it — the same failures occur when running the lookups directly from the router itself.
- Signal quality as the sole cause — the failures are protocol-selective, which radio-layer packet loss would not be.
Active MBN profile is Commercial-DT-VOLTE (0x0A011F1F, 202409181).
Has this been seen on RG520N or related modules? Is there a newer firmware revision (R03A03/R03A04 or later) that addresses UDP handling, and is there anything in the release notes covering this?