Where are the TTL of dynamically added records configured in bind?
I have a DNS-zone with standart $TTL set to 10 minutes. When the zone is updated, the hosts added get their own TTLs that differ from the zone default. The DHCP lease is configured to 24h.
$ORIGIN . $TTL 600 ; 10 minutes example IN SOA firefly.example. postmaster.example. ( 2013102334 ; serial 28800 ; refresh (8 hours) 7200 ; retry (2 hours) 2419200 ; expire (4 weeks) 86400 ; minimum (1 day) ) NS firefly.example. $ORIGIN mqmedia. $TTL 18000 ; 5 hours Andreass-MBP A 192.168.1.79 TXT "31fdf53482504a9965e4e7a210ebfe6080" $TTL 600 ; 10 minutes atom-builder A 192.168.1.13 $TTL 86400 ; 1 day axis-00031c200982 A 192.168.1.47 TXT "311b67a2c49ae34eb511fa989cb22c9e65" axis-00031c205143 A 192.168.1.208 TXT "319dfebd7e94f89fa7ebda8e87d6702499" axis-00031c2d0067 A 192.168.1.45 TXT "31f70f97c582af3ace2ec4773a19edd451" $TTL 18000 ; 5 hours axis-00408c99d062 A 192.168.1.168 TXT "3141073fe7f825c3c3a9daa1b864ab6afd" axis-00408cac034d A 192.168.1.209 TXT "317e6bffaf74e74855f944b1e18ba6aac8" axis-00408cd5b244 A 192.168.1.69 TXT "31d7bebe14245b2f42f8d601554eb284d5" axis-00408cdb9d15 A 192.168.1.213 TXT "31aaa279559559302bf51db4cb8e2b69f8"
Best Answer
The TTL is always configured at the zone file. It may be set as default, using
$TTL
on the beginning of the file; as individual$TTL
statements spread through the file, and influencing the records below it; or even on the record itself.When the server does a nsupdate to add the record for your host, bind will check to see if there is any TTL already present, marking
$TTL 86400
, and add the record below it, if not, it will add the$TTL
for the specified time and the record below it.