6 ms·

"The length limit of a DNS TXT record is 255 characters." Nope. That's the maximum length of a TXT record string. TXT record strings with the same owner name g

by dc396 4mo ago

"The length limit of a DNS TXT record is 255 characters." Nope. That's the maximum length of a TXT record string. TXT record strings with the same owner name get concatenated together. The maximum for a TXT record is 65,280 octets (which may or may not translate into characters depending on encoding). Also, you probably want to think about the implications of caching and TTL.

Bender 4mo ago
When you say "get concatenated together" are you perhaps thinking of how multiple SPF records get concatenated by MTA's? Because in ISC dig they are multiple distinct records, which is fine too. finger nochan.net "bing bing bong." "Catching up on HN"
- dc396 4mo ago
  No. It's been a while, but I believe if you use multiple TXTs, resolvers can reorder them as they see fit. For example, label IN TXT "foo " IN TXT "bar " IN TXT "baz" You can have any number of TXT RRs with a label, allowing up to 65,280 bytes. However, resolvers can reorder those 3 TXT RRs. If you put the text strings in quotes in a single TXT RR, e.g.: label IN TXT "foo " "bar " "baz" You'll get "foo bar baz" and each of the strings can be up to 255 bytes. I think (but I'm too lazy to verify) that the maximum length of a concatenated string is implementation dependent.
  - Bender 4mo ago
    for i in $(seq 100);do echo -en '0';done 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 test 69s in txt "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" nsd-checkzone nochan.net ./nochan.net.zone zone nochan.net is ok nsd-control reload nochan.net ok # from my laptop dig -t txt +short test.nochan.net "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" Still shows up as three quoted strings 100 characters long each but not 300 0's meaning no concatenation at least not when using dig which is what this thread is about.

by dc396 4mo ago

Bender 4mo ago

When you say "get concatenated together" are you perhaps thinking of how multiple SPF records get concatenated by MTA's? Because in ISC dig they are multiple distinct records, which is fine too. finger nochan.net "bing bing bong." "Catching up on HN"

dc396 4mo ago
No. It's been a while, but I believe if you use multiple TXTs, resolvers can reorder them as they see fit. For example, label IN TXT "foo " IN TXT "bar " IN TXT "baz" You can have any number of TXT RRs with a label, allowing up to 65,280 bytes. However, resolvers can reorder those 3 TXT RRs. If you put the text strings in quotes in a single TXT RR, e.g.: label IN TXT "foo " "bar " "baz" You'll get "foo bar baz" and each of the strings can be up to 255 bytes. I think (but I'm too lazy to verify) that the maximum length of a concatenated string is implementation dependent.
- Bender 4mo ago
  for i in $(seq 100);do echo -en '0';done 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 test 69s in txt "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" nsd-checkzone nochan.net ./nochan.net.zone zone nochan.net is ok nsd-control reload nochan.net ok # from my laptop dig -t txt +short test.nochan.net "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" Still shows up as three quoted strings 100 characters long each but not 300 0's meaning no concatenation at least not when using dig which is what this thread is about.