From a494cc74ad646540fa5b3a994e94f20d7652f62e Mon Sep 17 00:00:00 2001 From: cinap_lenrek Date: Sun, 28 Sep 2014 05:15:25 +0200 Subject: [PATCH] ndb/dns: request recursion only for local dns servers we used to set RD flag in requests unconditionally, which is fine by the standard but some dns server administrators seem to use it as a denial of service indicator (for ther non recursive authoritative nameservers) and ignore the request. so only set the RD flag when talking to local dns servers. --- sys/src/cmd/ndb/dnresolve.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/sys/src/cmd/ndb/dnresolve.c b/sys/src/cmd/ndb/dnresolve.c index be7b94d91..a93c29151 100644 --- a/sys/src/cmd/ndb/dnresolve.c +++ b/sys/src/cmd/ndb/dnresolve.c @@ -1326,16 +1326,22 @@ tcpquery(Query *qp, DNSmsg *mp, int depth, uchar *ibuf, uchar *obuf, int len, static int queryns(Query *qp, int depth, uchar *ibuf, uchar *obuf, ulong waitms, int inns) { - int ndest, len, replywaits, rv; + int ndest, len, replywaits, rv, flag; ushort req; uvlong endms; char buf[32]; uchar srcip[IPaddrlen]; Dest *p, *np, dest[Maxdest]; - /* pack request into a udp message */ req = rand(); - len = mkreq(qp->dp, qp->type, obuf, Frecurse|Oquery, req); + + /* request recursion only for local dns servers */ + flag = Oquery; + if(strncmp(qp->nsrp->owner->name, "local#", 6) == 0) + flag |= Frecurse; + + /* pack request into a udp message */ + len = mkreq(qp->dp, qp->type, obuf, flag, req); /* no server addresses yet */ memset(dest, 0, sizeof dest);