## page was renamed from DNS/毒盛/Guide/cache_overwriting
== DNS/毒盛/Guide/cache_overwriting ==

Sooel Son and Vitaly Shmatikov


5 Cache Overwriting

|| Define symbol || Trust level || Description||
|| trust ultimate || 8 ||This server is authoritative||
|| trust secure || 7 || Successfully DNSSEC validated||
|| trust authanswer ||6 || Answer from an authoritative server||
|| trust authauthority || 5 || Received in the auth section as an authority response||
|| trust answer || 4 || Answer from a non-authoritative server||
|| trust glue || 3 || Received in a referral response||
|| trust additional || 2 || Received in the add section of a response||

Table 2. Trust levels in BIND 9.4.1.

{{{
In BIND, a cached RRset is overwritten if the trust level of
the received RRset is higher or equal to the cached one and its TTL is longer. 
  NS-type RRsets received in a referral are an exception:
     they have the trust level 8 for the purposes of overwriting 
   (i.e., they always overwrite the records already present in the cache), but are stored with the trust level 3.
}}}
   かなり危ないことが分かる。　<level 8 扱いで、常にキャッシュを上書きする。>


In Unbound, the absolute trust levels are different, but the relative order is the same.
Therefore, we use the same trust-level model for BIND and Unbound.

MaraDNS does not use trust levels.