On 8/31/11 10:13 PM, "风河" <short...@gmail.com> wrote: > Hello, > > I found that some queries have got the response which has additional > section, but some haven't. > For example, this query with www.google.com got the answer with > additional section set: > > $ dig www.google.com > ;; MSG SIZE rcvd: 236 > $ dig www.google.com > > ;; MSG SIZE rcvd: 220
> My question is under what condition the nameserver answers the query > with additional section set? When there is sufficient space for the additional information in the packet, it is sent. If the answer and authority were too big to fit in the packet, then the DNS server is supposed to set the "truncated data" bit so that the resolver knows it is supposed to try TCP or EDNS0 to get a larger response. But the truncated data bit is not sent when the only things truncated are additional information records. When querying google.com A using edns=0, the size of the message is 271 bytes, including all 4 RRs in the additional section. -- Daniel J McDonald, CCIE # 2495, CISSP # 78281 _______________________________________________ Please visit https://lists.isc.org/mailman/listinfo/bind-users to unsubscribe from this list bind-users mailing list bind-users@lists.isc.org https://lists.isc.org/mailman/listinfo/bind-users
