4 ms·

Any thoughts on where/how is this 'home in' state is saved? Other the cache and filtering/acl state resolvers should be stateless, so would be interested in any

by mmmooo 13y ago

Any thoughts on where/how is this 'home in' state is saved? Other the cache and filtering/acl state resolvers should be stateless, so would be interested in any details, especially if this is on a per-zone, or per-set of nameservers or etc basis. I've never seen bind9 act like this.

colmmacc 13y ago
I haven't read the bind source in a long time, but my best guess is that it's in memory. http://docstore.mik.ua/orelly/networking_2ndEd/dns/ch02_06.htm http://docstore.mik.ua/orelly/networking_2ndEd/dns/ch02_06.h... Has some details, and I believe Bind and PowerDNS call it "Smoothed RTT" or SRTT.
- mmmooo 13y ago
  interesting, not a ton of details of how. off to the source I go, thanks. sounds like it assigns a 'score' of some sort to each authoritative ns.
  - isb 13y ago
    This might help - section 4.4 has formal details on the Bind server selection algorithms: http://ocw.mit.edu/courses/mathematics/18-996-topics-in-theoretical-computer-science-internet-research-problems-spring-2002/lecture-notes/dns.pdf http://ocw.mit.edu/courses/mathematics/18-996-topics-in-theo...
    - mmmooo 13y ago
      yep definitely, an interesting implementation, and certainly almost impossible to guess from passive observation. thanks.
  - dsl 13y ago
    BIND assigns a score based on every IP it talks to and a hit rate. (so if ns1.foo.com resolves to 3 IPs, each is tracked individually, same if ns1.bar.com and ns1.baz.com are the same IP) It is a pretty small cache, maybe like 1024? This is all from fuzzy 5 year old memory.