| BIND does not have many implementation limits, or at least not limits you easily bump into. Most of these limits are not explicitly documented, and for that reason, I might easily have missed or misinterpreted some in spite of my best efforts. These are some of the limits in BIND 8.2.2P5: A slave zone can have only 16 masters. BIND will try only up to 16 NS records when making queries about a zone. The maximum concurrent inbound zone transfers is 20. BIND handles only 65,536 zones. BIND will issue only 20 queries to recursively resolve a name. The maximum SOA refresh interval is 2,419,200 seconds, or 4 weeks. The maximum retry interval is 1,209,600 seconds, or 2 weeks. Only 20 additional records in a query answer are handled. Domain names can be only 1,024 characters long in total. Software such as dig apparently thinks that 255 is a more reasonable limit, and this is in line with assumptions made other places, so stick to 255. Your kernel might also limit you to setting FQDN hostnames shorter than 255 characters. UDP DNS packets are restricted to 512 bytes. Under some new protocol extensions implemented in BIND 9, this is no longer true, though. These limits are encoded in various parts of the source code. Some of them are design limits, which are hard to get around. Some are protocol limits that you shouldn't try to get around (and if you do, you face interoperability issues), and some are just limits you can change by simply changing a #define in the source code and recompiling. If you want to change the source, you must be able to distinguish them from each other first. |
