
Using a GCP LB to provide DNS High-Availability
DNS uses UDP port 53 for most of it operations but relies on TCP for operations that requires the transmission of packets exceeding 512 bytes. When the message size exceeds 512 bytes, it triggers a ‘TC’ bit (Truncation) in DNS to inform the client that the message length has exceeded the allowed size. The client needs then to re-transmit over TCP (size limit is 64000 bytes). Back End Configuration If you happen to run the HC across a device like routers or firewall you will need to configure DNAT for those devices to properly reply back to the HC of … Continue reading Using a GCP LB to provide DNS High-Availability