Revert 68f6312d4bae30b78daafcd6f51dc441b8685b1e
The above is intended to increase robustness, but actually does the
opposite. The problem is that by ignoring SERVFAIL messages and hoping
for a better answer from another of the servers we've forwarded to,
we become vulnerable in the case that one or more of the configured
servers is down or not responding.
Consider the case that a domain is indeed BOGUS, and we've send the
query to n servers. With 68f6312d4bae30b78daafcd6f51dc441b8685b1e
we ignore the first n-1 SERVFAIL replies, and only return the
final n'th answer to the client. Now, if one of the servers we are
forwarding to is down, then we won't get all n replies, and the
client will never get an answer! This is a far more likely scenario
than a temporary SERVFAIL from only one of a set of notionally identical
servers, so, on the ground of robustness, we have to believe
any SERVFAIL answers we get, and return them to the client.
The client could be using the same recursive servers we are,
so it should, in theory, retry on SERVFAIL anyway.
diff --git a/src/forward.c b/src/forward.c
index 84bed20..df33b8e 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -957,8 +957,7 @@
we get a good reply from another server. Kill it when we've
had replies from all to avoid filling the forwarding table when
everything is broken */
- if (forward->forwardall == 0 || --forward->forwardall == 1 ||
- (RCODE(header) != REFUSED && RCODE(header) != SERVFAIL))
+ if (forward->forwardall == 0 || --forward->forwardall == 1 || RCODE(header) != REFUSED)
{
int check_rebind = 0, no_cache_dnssec = 0, cache_secure = 0, bogusanswer = 0;