bottom line: DNS' RFC notes that DNS queries over UDP are limited to 512 bytes. Does anybody know if this is enforced by major corporate firewalls?
long story: My company develops a product that should communicate between data centers. Since the typical user of this product (performance engineer) would not have access to firewall's settings, we would like to develop a method that bypasses firewalls with good rates of success. We thought of tunneling the application data over DNS TXT queries, since it seems that (within the WAN) firewalls tend to let DNS queries pass by. However, we are not very knowledgeable about common firewall behavior and would like some help. Specifically, we are wondering whether the big-brand firewalls block DNS queries over UDP that are longer than 512 bytes.