On Fri, Mar 25, 2005 at 05:43:49AM -0700,
David MacQuigg <dmquigg-spf(_at_)yahoo(_dot_)com> wrote
a message of 56 lines which said:
What happens when DNS messages exceed 512 bytes?
RFC 2181:
Where TC is set, the partial RRSet that would not completely fit may
be left in the response. When a DNS client receives a reply with TC
set, it should ignore that response, and query again, using a
mechanism, such as a TCP connection, that will permit larger replies.
RFC 2671 describes an alternative to TCP, EDNS, which is widely
deployed:
4.5. The sender's UDP payload size (which OPT stores in the RR CLASS
field) is the number of octets of the largest UDP payload that can
be reassembled and delivered in the sender's network stack. Note
that path MTU, with or without fragmentation, may be smaller than
this.
Section 14.7 Caching, in Stevens TCP/IP Illustrated says "To reduce
the DNS traffic on the Internet, all name servers employ a cache."
The problem with the DNS specification is that "name server" means two
different things. To complicate the matter, these two different things
are both implemented in BIND (but not in all name server software) and
often run together in the same daemon:
* a proxy name server resolves queries on behalf of dumb clients. It
caches the results. It is recursive.
* an authoritative name server knows the data (from a zone file or
from a DBMS) for one or several zones and replies to the queries of
the proxies. It has nothing to cache. It is iterative.
-------
Sender Policy Framework: http://spf.pobox.com/
Archives at http://archives.listbox.com/spf-discuss/current/
Read the whitepaper! http://spf.pobox.com/whitepaper.pdf
To unsubscribe, change your address, or temporarily deactivate your
subscription,
please go to
http://v2.listbox.com/member/?listname=spf-discuss(_at_)v2(_dot_)listbox(_dot_)com
-------
Sender Policy Framework: http://spf.pobox.com/
Archives at http://archives.listbox.com/spf-discuss/current/
Read the whitepaper! http://spf.pobox.com/whitepaper.pdf
To unsubscribe, change your address, or temporarily deactivate your
subscription,
please go to
http://v2.listbox.com/member/?listname=spf-discuss(_at_)v2(_dot_)listbox(_dot_)com