draft-ietf-dnsind-notify-01.txt   draft-ietf-dnsind-notify-02.txt 
Internet Area P. Vixie Internet Area P. Vixie
DNSIND Working Group Vixie Enterprises DNSIND Working Group Vixie Enterprises
<draft-ietf-dnsind-notify-02.txt> 09-July-1995
Updates: RFC 1035 Updates: RFC 1035
Notify: a mechanism for prompt notification of authority zone changes Notify: a mechanism for prompt notification of authority zone changes
Status of this Memo Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
skipping to change at page 1, line 30 skipping to change at page 1, line 30
material or to cite them other than as `work in progress.' material or to cite them other than as `work in progress.'
To learn the current status of any Internet-Draft, please check the To learn the current status of any Internet-Draft, please check the
``1id-abstracts.txt'' listing contained in the Internet- Drafts ``1id-abstracts.txt'' listing contained in the Internet- Drafts
Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net
(Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific
Rim). Rim).
Abstract Abstract
This draft describes a new DNS opcode, NOTIFY, by which a master This draft describes the NOTIFY opcode for DNS, by which a master
server advises a set of slave servers that the master's data has been server advises a set of slave servers that the master's data has been
changed and that a query should be initiated to discover the new changed and that a query should be initiated to discover the new
data. data.
0. Rationale and Scope 0. Rationale and Scope
Slow propagation of new and changed data in a DNS zone can be due to Slow propagation of new and changed data in a DNS zone can be due to
a zone's relatively long refresh times. Longer refresh times are a zone's relatively long refresh times. Longer refresh times are
beneficial in that they reduce load on the master servers, but that beneficial in that they reduce load on the master servers, but that
benefit comes at the cost of having changes not become visible to DNS benefit comes at the cost of having changes not become visible to DNS
clients until a sometimes inconvenient interval has elapsed. clients until a potentially lengthy interval has elapsed.
The Notify DNS message allows master servers to inform slave servers The DNS NOTIFY transaction allows master servers to inform slave
when data have changed, an interrupt as opposed to poll model, which servers when data have changed -- an interrupt as opposed to poll
it is hoped will reduce propagation delay while not unduly increasing model -- which it is hoped will reduce propagation delay while not
the masters' load. unduly increasing the masters' load.
This document defines a new DNS opcode called NOTIFY whose numeric This document defines a new DNS opcode called NOTIFY whose numeric
value is four (4). All fields not otherwise specified must contain value is four (4). All fields not otherwise specified must contain
<draft-ietf-dnsind-notify-02.txt>- 2 - 09-July-1995
binary zero, and implementations must ignore any request or response binary zero, and implementations must ignore any request or response
packets where this is not the case. packets where this is not the case.
This document intentionally gives more definition to the roles of DNS This document intentionally gives more definition to the roles of
master and slave servers, their enumeration in NS RRs, and the SOA ``Master,'' ``Slave'' and ``Stealth'' servers, their enumeration in
MNAME field. In that sense, this document can be considered an NS RRs, and the SOA MNAME field. In that sense, this document can be
addendum to RFC 1035. considered an addendum to RFC 1035.
1. NOTIFY Message 1. NOTIFY Message
When a master has updated one or more RRs in which slave servers may When a master has updated one or more RRs in which slave servers may
be interested, the master may send the changed RR's name, type, and be interested, the master may send the changed RR's name, type, and
optionally, new RDATA(s), to each known slave server using a best optionally, new RDATA(s), to each known slave server using a best
efforts protocol based on the NOTIFY opcode. efforts protocol based on the NOTIFY opcode.
NOTIFY is similar to QUERY in that it has an initiator packet with QR NOTIFY is similar to QUERY in that it has an initiator packet with QR
``set'' and a response packet with QR ``clear''. The response packet ``set'' and a response packet with QR ``clear''. The response packet
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A master repeatedly sends NOTIFY to a slave until either too many A master repeatedly sends NOTIFY to a slave until either too many
copies have been sent (a ``timeout'') or until a NOTIFY-QR is copies have been sent (a ``timeout'') or until a NOTIFY-QR is
received from the slave with a matching query ID, QNAME, and IP received from the slave with a matching query ID, QNAME, and IP
source address. The interval between retransmissions, and the total source address. The interval between retransmissions, and the total
number of retransmissions, should be operational parameters number of retransmissions, should be operational parameters
specifiable by the name server administrator, perhaps on a per-zone specifiable by the name server administrator, perhaps on a per-zone
basis. Reasonable defaults are a 60 second interval and 5 attempts. basis. Reasonable defaults are a 60 second interval and 5 attempts.
It is also reasonable to use additive or exponential backoff for the It is also reasonable to use additive or exponential backoff for the
retry interval. retry interval.
A NOTIFY packet has QCOUNT>0, ANCOUNT>=0, AUCOUNT=ADCOUNT=0. If A NOTIFY packet has QCOUNT>0, ANCOUNT>=0, AUCOUNT=0, ADCOUNT=0. If
ANCOUNT is nonzero, then the answer section represents an unsecure ANCOUNT is nonzero, then the answer section represents an unsecure
hint at the new RR set for this <QNAME,QCLASS,QTYPE>. A slave hint at the new RR set for this <QNAME,QCLASS,QTYPE>. A slave
receiving such an update is free to treat equivilence of this answer receiving such an update is free to treat equivilence of this answer
section with its local data as a ``no further work needs to be done'' section with its local data as a ``no further work needs to be done''
indication; if ANCOUNT=0 or the answer section is present and differs indication; if ANCOUNT=0 or the answer section is present and differs
from the slave's local data, then the slave is required to query its from the slave's local data, then the slave should query its defined
defined masters to retrieve the new data. In no case shall the masters to retrieve the new data. In no case shall the answer
answer section of a NOTIFY-!QR be used to update a slave's local section of a NOTIFY-!QR be used to update a slave's local data, or to
data, or to indicate that a zone transfer needs to be undertaken, or indicate that a zone transfer needs to be undertaken, or to change
to change the slave's zone refresh timers. Only a ``data present; the slave's zone refresh timers. Only a ``data present; data same''
data same'' condition can lead a slave to act differently based on a condition can lead a slave to act differently based on a NOTIFY-!QR
NOTIFY-!QR answer section. answer section.
In the future, it is expected that this specification will be amended In the future, it is expected that this specification will be amended
such that AUCOUNT or ADCOUNT may be allowed to be nonzero, to such that AUCOUNT or ADCOUNT may be allowed to be nonzero, to
indicate that the new data is signed and secure, and can therefore be indicate that the new data is signed and secure, and can therefore be
<draft-ietf-dnsind-notify-02.txt>- 3 - 09-July-1995
trusted. Until that work has been completed and a standard has been trusted. Until that work has been completed and a standard has been
made, any packet with AUCOUNT<>0 or ADCOUNT<>0 must be ignored by any made, any packet with AUCOUNT<>0 or ADCOUNT<>0 must be ignored by any
server receiving it. server receiving it.
NOTE
There is at this time no specification for incremental
updates; the slave servers are NOT free to overlay a
previous AXFR's data with data from a non-AXFR QUERY, even
if that QUERY occurred as a result of a NOTIFY and the
response to the QUERY is authoritative. NOTIFY may be the
basis on which incremental updates are specified, but at
this time it is only an ``update hint.''
If a slave receives a NOTIFY request from a host which is not listed If a slave receives a NOTIFY request from a host which is not listed
in the slave's static list of masters for the zone containing the in the slave's static list of masters for the zone containing the
QNAME, it must ignore the request and may log an error in its QNAME, it must ignore the request and may log an error in its
operations log. Implementations must also ignore NOTIFY requests operations log.
that come from a UDP port other than the DNS port (53), as these are
by definition not from another name server.
The only useful hint at this time is that the SOA RR has changed. The only useful hint at this time is that the SOA RR has changed.
Upon completion of a NOTIFY transaction for QTYPE=SOA, the slave Upon completion of a NOTIFY transaction for QTYPE=SOA, the slave
should behave as though the zone given in the QNAME had reached its should behave as though the zone given in the QNAME had reached its
REFRESH interval [see RFC 1035], i.e., it should query the master REFRESH interval [see RFC 1035], i.e., it should query the master
that sent the NOTIFY request, asking for the same QTYPE and QNAME as that sent the NOTIFY request, asking for the same QTYPE and QNAME as
were given in the NOTIFY request. If an answer comes, and the SOA RR were given in the NOTIFY request. If an answer comes, and the SOA RR
has a newer serial number than the slave's current copy of the zone, has a newer serial number than the slave's current copy of the zone,
then a zone transfer should be initiated. then a zone transfer should be initiated.
2. Some Definitions and Two Requirements 2. Some Definitions and Two Requirements
Definition: the Primary Master Server is the host at the
root of the AXFR/IXFR dependency graph. The primary master is
named in the zone's SOA MNAME field, and optionally by an NS RR.
The source of the primary master's zone data is external to the
DNS, for example, the host's file system.
Definition: a Master Server is any authoritative server configured Definition: a Master Server is any authoritative server configured
to be the source of AXFR from one or more slave servers. It is to be the source of AXFR/IXFR from one or more slave servers.
named in an NS RR for the zone. It is named in an NS RR for the zone.
Definition: a Slave Server is a quasi-authoritative server which Definition: a Slave Server is a an authoritative server which
uses AXFR to retrieve the zone. All slave servers are named in uses AXFR/IXFR to retrieve the zone. All slave servers are
the NS RRs for the zone. Slaves which use AXFR to retrieve a named in the NS RRs for the zone. A slave server can also act
zone, and which respect the SOA timeouts, but which are not as a master in the case of a deep AXFR/IXFR tree.
listed in the zone's NS RR set, are ``unregistered''.
Unregistered slaves are sometimes used to hot-wire a cache, and
are outside the scope of the DNS prototols, but NOTIFY defines
optional support for them. Note that a server is not, in the
strict RFC 1035 sense of the term, ``authoritative'' for a zones
it loads via AXFR, unless it is listed in the zone's NS RR set.
The question of whether such servers should set the AA bit on
responses they generate from such data, remains open.
Definition: the Primary Master Server is the master server at the Definition: a Stealth Server is a potentially authoritative server
root of the AXFR dependency graph. The primary master is named which
in the zone's SOA MNAME field and by an NS RR. The source of uses AXFR/IXFR as described above for ``Slave Server.'' Stealth
the primary master's zone data is external to the DNS and is not servers are not named in the NS RRs for the zone, and are thus
a formal concern of this document. useful only as a way to ``hotwire the cache.'' A stealth server
will, unless explicitly configured to do otherwise, sets the AA
bit in responses and is capable of acting as a Master. A
stealth server will only be recognized by other servers if it
sends queries from the DNS service port (UDP 53).
Requirement: for a zone to make use of the NOTIFY protocol, its Requirement: for a zone to make use of the NOTIFY protocol, its
servers must be organized into a dependency graph such that servers must be organized into a dependency graph such that
there is a primary master, and all other servers must use AXFR there is a primary master, and all other servers must use AXFR
<draft-ietf-dnsind-notify-02.txt>- 4 - 09-July-1995
either from the primary master or from some slave which is also either from the primary master or from some slave which is also
a master. A slave which is also a master is referred to later a master. No loops are permitted in the AXFR dependency graph.
in this document as a ``slave-master''. No loops are permitted
in the AXFR dependency graph.
Requirement: for a zone to make use of the NOTIFY protocol, all Requirement: for a zone to make use of the NOTIFY protocol, all
servers named in the zone's NS RR set (under the delegation servers named in the zone's NS RR set (under the delegation
point) must use AXFR to do zone updates, or, if some other point) must use AXFR to do zone updates, or, if some other
protocol is used (e.g., FTP or NFS), it must simulate the retry protocol is used (e.g., FTP or NFS), it must simulate all of the
and refresh semantics of SOA/AXFR. semantics of SOA/AXFR/IXFR.
3. Semantic Details 3. Semantic Details
Master servers should maintain a list of slaves which have queried Master servers should maintain a list of stealth servers which have
the SOA of the zone within the last SOA REFRESH interval. On a best queried the SOA of the zone within the last SOA REFRESH interval. On
efforts basis, NOTIFY requests should be sent to each slave server a best efforts basis, NOTIFY requests should be sent to each slave
address whose last successful query for the changed RR's name and server address whose last successful query for the changed RR's name
type was within that interval. Note that queries from UDP ports and type was within that interval. (Retaining this state information
other than the DNS service port (53) are not subject to this across host reboots is optional, but it is reasonable to simply
requirement, since they cannot (by definition) be from other name execute a NOTIFY transaction on each authority zone when a server
servers. first starts.)
In a deep tree where some slaves AXFR new zones from other slaves, it In a deep tree where some slaves fetch new zones from other slaves,
can happen that some slaves will receive multiple NOTIFYs of the same it can happen that some slaves will receive multiple NOTIFYs of the
RR change: one from the primary master, and one from each slave- same RR change: one from the primary master, and one from each other
master from which it has requested this RR's name and type within the slave from which it has requested this RR's name and type within the
last SOA REFRESH interval. The protocol supports this multiplicity last SOA REFRESH interval. The protocol supports this multiplicity
by requiring that NOTIFY be sent by a slave-master only AFTER it has by requiring that NOTIFY be sent by a slave/master only AFTER it has
updated the RR. With an SOA NOTIFY, the RR can only change after a updated the RR. With an SOA NOTIFY, the RR can only change after a
subsequent AXFR. Thus, barring delivery reordering, the last NOTIFY subsequent AXFR/IXFR. Thus, barring delivery reordering, the last
any slave receives will be the one indicating the latest change. NOTIFY any slave receives will be the one indicating the latest
Since a slave always requests SOAs and AXFRs only from its locally change. Since a slave always requests SOAs and AXFR/IXFRs only from
designated masters, it will have an opportunity to retry its SOA its locally designated masters, it will have an opportunity to retry
query after its masters have completed each zone update. its SOA query after its masters have completed each zone update.
If a master server seeks to avoid causing a large number of If a master server seeks to avoid causing a large number of
simultaneous outbound zone transfers, it may delay for an arbitrary simultaneous outbound zone transfers, it may delay for an arbitrary
length of time before sending a NOTIFY message to any given slave. length of time before sending a NOTIFY message to any given slave.
It is expected that the time will be chosen at random, so that each It is expected that the time will be chosen at random, so that each
slave will begin its transfer at a unique time, perhaps with some slave will begin its transfer at a unique time, perhaps with some
weighting so that pending outbound NOTIFY's are more likely to be weighting so that pending outbound NOTIFY's are more likely to be
sent out whenever a zone transfer completes. The delay shall not in sent out whenever a zone transfer completes. The delay shall not in
any case be longer than the SOA REFRESH time, and should be a any case be longer than the SOA REFRESH time, and should be a
parameter that each primary master name server can specify, perhaps parameter that each primary master name server can specify, perhaps
on a per-zone basis. Random delays of between 30 and 60 seconds on a per-zone basis. Random delays of between 30 and 60 seconds
would seem adequate if the servers share a LAN and the zones are less would seem adequate if the servers share a LAN and the zones are less
than a megabyte in size. than a megabyte in size.
A slave which receives a valid NOTIFY should defer action on any A slave which receives a valid NOTIFY should defer action on any
subsequent NOTIFY with the same <QNAME,QCLASS,QTYPE> until it has subsequent NOTIFY with the same <QNAME,QCLASS,QTYPE> until it has
<draft-ietf-dnsind-notify-02.txt>- 5 - 09-July-1995
completed the transaction begun by the first NOTIFY. This duplicate completed the transaction begun by the first NOTIFY. This duplicate
rejection is necessary to avoid having multiplicitous notifications rejection is necessary to avoid having multiple notifications lead to
lead to pummeling the master server. pummeling the master server.
The rest of this section is concerned only with SOA NOTIFY. The rest of this section is concerned only with SOA NOTIFY.
3.a. Zone has Updated on Primary Master 3.a. Zone has Updated on Primary Master
Primary master sends a NOTIFY request to all servers named in the NS Primary master sends a NOTIFY request to all servers named in the NS
RR, except the one that is also named in the SOA MNAME, and RR, except the one that is also named in the SOA MNAME, and
optionally to all name servers which have queried for this SOA within optionally to all name servers which have queried for this SOA within
the last SOA REFRESH interval. The NOTIFY has the following the last SOA REFRESH interval. The NOTIFY has the following
characteristics: characteristics:
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qcount: 1 qcount: 1
qname: (zone name) qname: (zone name)
qclass: C_IN qclass: C_IN
qtype: T_SOA qtype: T_SOA
ancount, aucount, adcount: 0 ancount, aucount, adcount: 0
Note that setting any flag other than AA should cause slave servers Note that setting any flag other than AA should cause slave servers
to ignore this query. Only AA is defined, the others all must to ignore this query. Only AA is defined, the others all must
contain binary zero. contain binary zero.
3.a.1. Zone has Updated on Slave-Master 3.a.1. Zone has Updated on a Slave that is also a Master
As above in 3.a, except that only those authoritative name servers As above in 3.a, except that only those authoritative name servers
(i.e., those listed in the zone's NS RR set) which have queried for (i.e., those listed in the zone's NS RR set) which have queried for
this name and type within the SOA REFRESH interval need to be this name and type within the SOA REFRESH interval need to be
notified. Optionally, the slave-master may send to all servers which notified. Optionally, the slave/master may send to all servers which
have sent such recent queries, without regard to whether they are have sent such recent queries, without regard to whether they are
listed in the zone's NS RR set. listed in the zone's NS RR set.
3.b. Slave Receives a NOTIFY Packet from a Master 3.b. Slave Receives a NOTIFY Packet from a Master
When a slave server receives a NOTIFY request from one of its locally When a slave server receives a NOTIFY request from one of its locally
designated masters for the zone enclosing the given QNAME, with designated masters for the zone enclosing the given QNAME, with
QTYPE=SOA and !QR, it should enter the state it would if the zone's QTYPE=SOA and !QR, it should enter the state it would if the zone's
refresh timer had expired. It will also send a NOTIFY response back refresh timer had expired. It will also send a NOTIFY response back
to the NOTIFY request's source, with the following characteristics: to the NOTIFY request's source, with the following characteristics:
query ID: (same) query ID: (same)
op: NOTIFY op: NOTIFY
resp: NOERROR resp: NOERROR
<draft-ietf-dnsind-notify-02.txt>- 6 - 09-July-1995
flags: QR AA flags: QR AA
qcount: 1 qcount: 1
qname: (zone name) qname: (zone name)
qclass: C_IN qclass: C_IN
qtype: T_SOA qtype: T_SOA
ancount, aucount, adcount: 0 ancount, aucount, adcount: 0
Note that this is intentionally identical to the NOTIFY request, Note that this is intentionally identical to the NOTIFY request,
except that the QR bit is also set. Note, also, that the query ID except that the QR bit is also set. Note, also, that the query ID
must be the same as was received in the NOTIFY request. must be the same as was received in the NOTIFY request.
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