1 Internet Engineering Task Force (IETF)                       W. Hardaker   
    2 Request for Comments: 7477                                 Parsons, Inc.   
    3 Category: Standards Track                                     March 2015   
    4 ISSN: 2070-1721                                                            
    7                  Child-to-Parent Synchronization in DNS                    
    9 Abstract                                                                   
   11    This document specifies how a child zone in the DNS can publish a       
   12    record to indicate to a parental agent that the parental agent may      
   13    copy and process certain records from the child zone.  The existence    
   14    of the record and any change in its value can be monitored by a         
   15    parental agent and acted on depending on local policy.                  
   17 Status of This Memo                                                        
   19    This is an Internet Standards Track document.                           
   21    This document is a product of the Internet Engineering Task Force       
   22    (IETF).  It represents the consensus of the IETF community.  It has     
   23    received public review and has been approved for publication by the     
   24    Internet Engineering Steering Group (IESG).  Further information on     
   25    Internet Standards is available in Section 2 of RFC 5741.               
   27    Information about the current status of this document, any errata,      
   28    and how to provide feedback on it may be obtained at                    
   29    http://www.rfc-editor.org/info/rfc7477.                                 
   31 Copyright Notice                                                           
   33    Copyright (c) 2015 IETF Trust and the persons identified as the         
   34    document authors.  All rights reserved.                                 
   36    This document is subject to BCP 78 and the IETF Trust's Legal           
   37    Provisions Relating to IETF Documents                                   
   38    (http://trustee.ietf.org/license-info) in effect on the date of         
   39    publication of this document.  Please review these documents            
   40    carefully, as they describe your rights and restrictions with respect   
   41    to this document.  Code Components extracted from this document must    
   42    include Simplified BSD License text as described in Section 4.e of      
   43    the Trust Legal Provisions and are provided without warranty as         
   44    described in the Simplified BSD License.                                
   52 Hardaker                     Standards Track                    [Page 1]   

   53 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
   56 Table of Contents                                                          
   58    1. Introduction ....................................................2   
   59       1.1. Terminology Used in This Document ..........................3   
   60    2. Definition of the CSYNC RRType ..................................3   
   61       2.1. The CSYNC Resource Record Format ...........................4   
   62            2.1.1. The CSYNC Resource Record Wire Format ...............4   
   63            2.1.2. The CSYNC Presentation Format .......................6   
   64            2.1.3. CSYNC RR Example ....................................6   
   65    3. CSYNC Data Processing ...........................................6   
   66       3.1. Processing Procedure .......................................7   
   67       3.2. CSYNC Record Types .........................................8   
   68            3.2.1. The NS type .........................................8   
   69            3.2.2. The A and AAAA Types ................................9   
   70    4. Operational Considerations ......................................9   
   71       4.1. Error Reporting ...........................................10   
   72       4.2. Child Nameserver Selection ................................10   
   73       4.3. Out-of-Bailiwick NS Records ...............................10   
   74       4.4. Documented Parental Agent Type Support ....................11   
   75       4.5. Removal of the CSYNC Records ..............................11   
   76       4.6. Parent/Child/Grandchild Glue Synchronization ..............12   
   77    5. Security Considerations ........................................12   
   78    6. IANA Considerations ............................................12   
   79    7. References .....................................................13   
   80       7.1. Normative References ......................................13   
   81       7.2. Informative References ....................................14   
   82    Acknowledgments ...................................................15   
   83    Author's Address ..................................................15   
   85 1.  Introduction                                                           
   87    This document specifies how a child zone in the DNS ([RFC1034]          
   88    [RFC1035]) can publish a record to indicate to a parental agent (see    
   89    Section 1.1 for a definition of "parental agent") that it can copy      
   90    and process certain records from the child zone.  The existence of      
   91    the record and any change in its value can be monitored by a parental   
   92    agent and acted on depending on local policy.                           
   94    Currently, some resource records (RRs) in a parent zone are typically   
   95    expected to be in sync with the source data in the child's zone.  The   
   96    most common records that should match are the nameserver (NS) records   
   97    and any necessary associated address records (A and AAAA), also known   
   98    as "glue records".  These records are referred to as "delegation        
   99    records".                                                               
  101    It has been challenging for operators of child DNS zones to update      
  102    their delegation records within the parent's set in a timely fashion.   
  103    These difficulties may stem from operator laziness as well as from      
  107 Hardaker                     Standards Track                    [Page 2]   

  108 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  111    the complexities of maintaining a large number of DNS zones.  Having    
  112    an automated mechanism for signaling updates will greatly ease the      
  113    child zone operator's maintenance burden and improve the robustness     
  114    of the DNS as a whole.                                                  
  116    This document introduces a new Resource Record Type (RRType) named      
  117    "CSYNC" that indicates which delegation records published by a child    
  118    DNS operator should be processed by a parental agent and used to        
  119    update the parent zone's DNS data.                                      
  121    This specification was not designed to synchronize DNSSEC security      
  122    records, such as DS RRsets.  For a solution to this problem, see the    
  123    complementary solution [RFC7344], which is designed to maintain         
  124    security delegation information.  In addition, this specification       
  125    does not address how to perform bootstrapping operations, including     
  126    to get the required initial DNSSEC-secured operating environment in     
  127    place.                                                                  
  129 1.1.  Terminology Used in This Document                                    
  131    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",     
  132    "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this    
  133    document are to be interpreted as described in [RFC2119].               
  135    Terminology describing relationships between the interacting roles      
  136    involved in this document are defined in the following list:            
  138    Child:  The entity on record that has the delegation of the domain      
  139       from the parent                                                      
  141    Parent:  The domain in which the child is registered                    
  143    Child DNS operator:  The entity that maintains and publishes the zone   
  144       information for the child DNS                                        
  146    Parental agent:  The entity that the child has relationship with, to    
  147       change its delegation information                                    
  149 2.  Definition of the CSYNC RRType                                         
  151    The CSYNC RRType contains, in its RDATA component, these parts: an      
  152    SOA serial number, a set of flags, and a simple bit-list indicating     
  153    the DNS RRTypes in the child that should be processed by the parental   
  154    agent in order to modify the DNS delegation records within the          
  155    parent's zone for the child DNS operator.  Child DNS operators          
  156    wanting a parental agent to perform the synchronization steps           
  157    outlined in this document MUST publish a CSYNC record at the apex of    
  158    the child zone.  Parental agent implementations MAY choose to query     
  162 Hardaker                     Standards Track                    [Page 3]   

  163 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  166    child zones for this record and process DNS record data as indicated    
  167    by the Type Bit Map field in the RDATA of the CSYNC record.  How the    
  168    data is processed is described in Section 3.                            
  170    Parental agents MUST process the entire set of child data indicated     
  171    by the Type Bit Map field (i.e., all record types indicated along       
  172    with all of the necessary records to support processing of that type)   
  173    or else parental agents MUST NOT make any changes to parental records   
  174    at all.  Errors due to unsupported Type Bit Map bits, or otherwise      

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GLOBAL V. Risk, ISC.orgBIND 9 implementation note2022-08-15

This RFC is implemented in BIND 9.18 (all versions).

  175    nonpunishable data, SHALL result in no change to the parent zone's      
  176    delegation information for the child.  Parental agents MUST ignore a    
  177    child's CSYNC RDATA set if multiple CSYNC resource records are found;   
  178    only a single CSYNC record should ever be present.                      
  180    The parental agent MUST perform DNSSEC validation ([RFC4033]            
  181    [RFC4034] [RFC4035]), of the CSYNC RRType data and MUST perform         
  182    DNSSEC validation of any data to be copied from the child to the        
  183    parent.  Parents MUST NOT process any data from any of these records    
  184    if any of the validation results indicate anything other than           
  185    "Secure" [RFC4034] or if any the required data cannot be successfully   
  186    retrieved.                                                              
  188 2.1.  The CSYNC Resource Record Format                                     
  190 2.1.1.  The CSYNC Resource Record Wire Format                              
  192    The CSYNC RDATA consists of the following fields:                       
  194                           1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3      
  195       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      
  196      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     
  197      |                          SOA Serial                           |     
  198      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     
  199      |       Flags                   |            Type Bit Map       /     
  200      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     
  201      /                     Type Bit Map (continued)                  /     
  202      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     
  204  The SOA Serial Field                                             
  206    The SOA Serial field contains a copy of the 32-bit SOA serial number    
  207    from the child zone.  If the soaminimum flag is set, parental agents    
  208    querying children's authoritative servers MUST NOT act on data from     
  209    zones advertising an SOA serial number less than this value.  See       
  210    [RFC1982] for properly implementing "less than" logic.  If the          
  211    soaminimum flag is not set, parental agents MUST ignore the value in    
  212    the SOA Serial field.  Clients can set the field to any value if the    
  213    soaminimum flag is unset, such as the number zero.                      
  217 Hardaker                     Standards Track                    [Page 4]   

  218 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  221    Note that a child zone's current SOA serial number may be greater       
  222    than the number indicated by the CSYNC record.  A child SHOULD update   
  223    the SOA Serial field in the CSYNC record every time the data being      
  224    referenced by the CSYNC record is changed (e.g., an NS record or        
  225    associated address record is changed).  A child MAY choose to update    
  226    the SOA Serial field to always match the current SOA Serial field.      
  228    Parental agents MAY cache SOA serial numbers from data they use and     
  229    refuse to process data from zones older than the last instance from     
  230    which they pulled data.                                                 
  232    Although Section 3.2 of [RFC1982] describes how to properly implement   
  233    a less-than comparison operation with SOA serial numbers that may       
  234    wrap beyond the 32-bit value in both the SOA record and the CSYNC       
  235    record, it is important that a child using the soaminimum flag must     
  236    not increment its SOA serial number value more than 2^16 within the     
  237    period of time that a parent might wait between polling the child for   
  238    the CSYNC record.                                                       
  240  The Flags Field                                                  
  242    The Flags field contains 16 bits of boolean flags that define           
  243    operations that affect the processing of the CSYNC record.  The flags   
  244    defined in this document are as follows:                                
  246       0x00 0x01: "immediate"                                               
  248       0x00 0x02: "soaminimum"                                              
  250    The definitions for how the flags are to be used can be found in        
  251    Section 3.                                                              
  253    The remaining flags are reserved for use by future specifications.      
  254    Undefined flags MUST be set to 0 by CSYNC publishers.  Parental         
  255    agents MUST NOT process a CSYNC record if it contains a 1 value for a   
  256    flag that is unknown to or unsupported by the parental agent.           
  258  The Type Bit Map Field                                         
  260    The Type Bit Map field indicates the record types to be processed by    
  261    the parental agent, according to the procedures in Section 3.  The      
  262    Type Bit Map field is encoded in the same way as the Type Bit Map       
  263    field of the NSEC record, described in [RFC4034], Section 4.1.2.  If    
  264    a bit has been set that a parental agent implementation does not        
  265    understand, the parental agent MUST NOT act upon the record.            
  266    Specifically, a parental agent must not simply copy the data, and it    
  267    must understand the semantics associated with a bit in the Type Bit     
  268    Map field that has been set to 1.                                       
  272 Hardaker                     Standards Track                    [Page 5]   

  273 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  276 2.1.2.  The CSYNC Presentation Format                                      
  278    The CSYNC presentation format is as follows:                            
  280       The SOA Serial field is represented as an integer.                   
  282       The Flags field is represented as an integer.                        
  284       The Type Bit Map field is represented as a sequence of RRType        
  285       mnemonics.  When the mnemonic is not known, the TYPE                 
  286       representation described in [RFC3597], Section 5, MUST be used.      
  287       Implementations that support parsing of presentation format          
  288       records SHOULD be able to read and understand these TYPE             
  289       representations as well.                                             
  291 2.1.3.  CSYNC RR Example                                                   
  293    The following CSYNC RR shows an example entry for "example.com" that    
  294    indicates the NS, A, and AAAA bits are set and should be processed by   
  295    the parental agent for example.com.  The parental agent should pull     
  296    data only from a zone using a minimum SOA serial number of 66 (0x42     
  297    in hexadecimal).                                                        
  299    example.com. 3600 IN CSYNC 66 3 A NS AAAA                               
  301    The RDATA component of the example CSYNC RR would be encoded on the     
  302    wire as follows:                                                        
  304     0x00 0x00 0x00 0x42             (SOA Serial)                           
  305     0x00 0x03                       (Flags = immediate | soaminimum)       
  306     0x00 0x04 0x60 0x00 0x00 0x08   (Type Bit Map)                         
  308 3.  CSYNC Data Processing                                                  
  310    The CSYNC record and associated data must be processed as an "all or    
  311    nothing" operation set.  If a parental agent fails to successfully      
  312    query for any of the required records, the whole operation MUST be      
  313    aborted.  (Note that a query resulting in "no records exist" as         
  314    proven by NSEC or NSEC3 is to be considered successful).                
  316    Parental agents MAY:                                                    
  318       Process the CSYNC record immediately if the "immediate" flag is      
  319       set.  If the "immediate" flag is not set, the parental agent MUST    
  320       NOT act until the zone administrator approves the operation          
  321       through an out-of-band mechanism (such as through pushing a button   
  322       via a web interface).                                                
  327 Hardaker                     Standards Track                    [Page 6]   

  328 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  331       Choose not to process the CSYNC record immediately, even if the      
  332       "immediate" flag is set.  That is, a parental agent might require    
  333       the child zone administrator approve the operation through an out-   
  334       of-band mechanism (such as through pushing a button via a web        
  335       interface).                                                          
  337    Note: how the approval is done out of band is outside the scope of      
  338    this document and is implementation specific to parental agents.        
  340 3.1.  Processing Procedure                                                 
  342    The following shows a sequence of steps that SHOULD be used when        
  343    collecting and processing CSYNC records from a child zone.  Because     
  344    DNS queries are not allowed to contain more than one "question" at a    
  345    time, a sequence of requests is needed.  When processing a CSYNC        
  346    transaction request, all DNS queries should be sent to a single         
  347    authoritative name server for the child zone.  To ensure a single       
  348    host is being addressed, DNS over TCP SHOULD be used to avoid           
  349    conversing with multiple nodes at an anycast address.                   
  351    1.  Query for the child zone's SOA record                               
  353    2.  Query for the child zone's CSYNC record                             
  355    3.  Query for the child zone's data records, as required by the CSYNC   
  356        record's Type Bit Map field                                         
  358        *  Note: if any of the resulting records being queried are not      
  359           authoritative within the child zone but rather in a grandchild   
  360           or deeper, SOA record queries must be made for the               
  361           grandchildren.  This will require the parental agent to          
  362           determine where the child/grandchild zone cuts occur.  Because   
  363           of the additional operational complexity, parental agents MAY    
  364           choose not to support this protocol with children making use     
  365           of records that are authoritative in the grandchildren.          
  367    4.  Query for the collected SOA records again, starting with the        
  368        deepest and ending with the SOA of the child's.                     
  370    If the SOA records from the first, middle, and last steps for a given   
  371    zone have different serial numbers (for example, because the zone was   
  372    edited and republished during the interval between steps 1 and 4),      
  373    then the CSYNC record obtained in the second set SHOULD NOT be          
  374    processed (rapidly changing child zones may need special                
  375    consideration or processing).  The operation MAY be restarted or        
  376    retried in the future.                                                  
  382 Hardaker                     Standards Track                    [Page 7]   

  383 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  386    If the soaminimum flag is set and the SOA serial numbers are equal      
  387    but less than the CSYNC record's SOA Serial field [RFC1982], the        
  388    record MUST NOT be processed.  If state is being kept by the parental   
  389    agent and the SOA serial number is less than the last time a CSYNC      
  390    record was processed, this CSYNC record SHOULD NOT be processed.        
  391    Similarly, if state is being kept by the parental agent and the SOA     
  392    Serial field of the CSYNC record is less than the SOA Serial field of   
  393    the CSYNC record from last time, then this CSYNC record SHOULD NOT be   
  394    processed.                                                              
  396    If a failure of any kind occurs while trying to obtain any of the       
  397    required data, or if DNSSEC fails to validate all of the data           
  398    returned for these queries as "secure", then this CSYNC record MUST     
  399    NOT be processed.                                                       
  401    See the "Operational Consideration" section (Section 4) for             
  402    additional guidance about processing.                                   
  404 3.2.  CSYNC Record Types                                                   
  406    This document defines how the following record types may be processed   
  407    if the CSYNC Type Bit Map field indicates they are to be processed.     
  409 3.2.1.  The NS type                                                        
  411    The NS type flag indicates that the NS records from the child zone      
  412    should be copied into the parent's delegation information records for   
  413    the child.                                                              
  415    NS records found within the child's zone should be copied verbatim      
  416    (with the exception of the Time to Live (TTL) field, for which the      
  417    parent MAY want to select a different value) and the result published   
  418    within the parent zone should be a set of NS records that match         
  419    exactly.  If the child has published a new NS record within their       
  420    set, this record should be added to the parent zone.  Similarly, if     
  421    NS records in the parent's delegation records for the child contain     
  422    records that have been removed in the child's NS set, then they         
  423    should be removed in the parent's set as well.                          
  425    Parental agents MAY refuse to perform NS updates if the replacement     
  426    records fail to meet NS record policies required by the parent zone     
  427    (e.g., "every child zone must have at least two NS records").           
  428    Parental agents MUST NOT perform NS updates if there are no NS          
  429    records returned in a query, as verified by DNSSEC denial-of-           
  430    existence protection.  This situation should never happen unless the    
  431    child nameservers are misconfigured.                                    
  437 Hardaker                     Standards Track                    [Page 8]   

  438 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  441    Note that it is permissible for a child's nameserver to return a        
  442    CSYNC record that removes the queried nameserver itself from the        
  443    future NS or address set.                                               
  445 3.2.2.  The A and AAAA Types                                               
  447    The A and AAAA type flags indicates that the A and AAAA address glue    
  448    records for in-bailiwick NS records within the child zone should be     
  449    copied verbatim (with the exception of the TTL field, for which the     
  450    parent MAY want to select a different value) into the parent's          
  451    delegation information.                                                 
  453    Queries should be sent by the parental agent to determine the A and     
  454    AAAA record addresses for each NS record within a NS set for the        
  455    child that are in bailiwick.                                            
  457    Note: only the matching types should be queried.  For example, if the   
  458    AAAA bit has not been set, then the AAAA records (if any) in the        
  459    parent's delegation should remain as is.  If a given address type is    
  460    set and the child's zone contains no data for that type (as proven by   
  461    appropriate NSEC or NSEC3 records), then the result in the parent's     
  462    delegation records for the child should be an empty set.  However, if   
  463    the end result of processing would leave no glue records present in     
  464    the parent zone for any of the of the in-bailiwick NS records, then     
  465    the parent MUST NOT update the glue address records.  That is, if the   
  466    result of the processing would leave no in-bailiwick A or AAAA          
  467    records when there are in-bailiwick NS records, then processing of      
  468    the address records cannot happen as it would leave the parent/child    
  469    relationship without any address linkage.                               
  471    The procedure for querying for A and AAAA records MUST occur after      
  472    the procedure, if required, for querying for NS records as defined in   
  473    Section 3.2.1.  This ensures that the right set of NS records is used   
  474    as provided by the current NS set of the child.  That is, for CSYNC     
  475    records that have the NS bit set, the NS set used should be the one     
  476    pulled from the child while processing the CSYNC record.  For CSYNC     
  477    records without the NS bit set, the existing NS records within the      
  478    parent should be used to determine which A and/or AAAA records to       
  479    update.                                                                 
  481 4.  Operational Considerations                                             
  483    There are a number of important operational aspects to consider when    
  484    deploying a CSYNC RRType.                                               
  492 Hardaker                     Standards Track                    [Page 9]   

  493 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  496 4.1.  Error Reporting                                                      
  498    There is no inline mechanism for a parental agent to report errors to   
  499    operators of child zones.  Thus, the only error reporting mechanisms    
  500    must be out of band, such as through a web console or over email.       
  501    Parental agents should, at a minimum, at least log errors encountered   
  502    when processing CSYNC records.  Child operators utilizing the           
  503    "immediate" flag that fail to see an update within the parental         
  504    agent's specified operational window should access the parental         
  505    agent's error logging interface to determine why an update failed to    
  506    be processed.                                                           
  508 4.2.  Child Nameserver Selection                                           
  510    Parental agents will need to poll child nameservers in search of        
  511    CSYNC records and related data records.                                 
  513    Parental agents MAY perform best-possible verification by querying      
  514    all NS records for available data to determine which has the most       
  515    recent SOA and CSYNC version (in an ideal world, they would all be      
  516    equal, but this is not possible in practice due to synchronization      
  517    delays and transfer failures).                                          
  519    Parental agents may offer a configuration interface to allow child      
  520    operators to specify which nameserver should be considered the master   
  521    to send data queries, too.  Note that this master could be a            
  522    different nameserver than the publicly listed nameservers in the NS     
  523    set (i.e., it may be a "hidden master").                                
  525    Parental agents with a large number of clients may choose to offer a    
  526    programmatic interface to let their children indicate that new CSYNC    
  527    records and data are available for polling rather than polling every    
  528    child on a frequent basis.                                              
  530    Children that wish to phase out a nameserver will need to publish the   
  531    CSYNC record to remove the nameserver and then wait for the parental    
  532    agent to process the published record before turning off the service.   
  533    This is required because the child cannot control which nameserver in   
  534    the existing NS set the parental agent may choose to query when         
  535    performing CSYNC processing.                                            
  537 4.3.  Out-of-Bailiwick NS Records                                          
  539    When a zone contains NS records where the domain name pointed at does   
  540    not fall within the zone itself, there is no way for the parent to      
  541    safely update the associated glue records.  Thus, the child DNS         
  542    operator MAY indicate that the NS records should be synchronized, and   
  547 Hardaker                     Standards Track                   [Page 10]   

  548 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  551    MAY set any glue record flags (A, AAAA) as well, but the parent will    
  552    only update those glue records that are below the child's delegation    
  553    point.                                                                  
  555    Children deploying NS records pointing to domain names within their     
  556    own children (the "grandchildren") SHOULD ensure the grandchildren's    
  557    associated glue records are properly set before publishing the CSYNC    
  558    record.  That is, it is imperative that proper communication and        
  559    synchronization exist between the child and the grandchild.             
  561 4.4.  Documented Parental Agent Type Support                               
  563    Parental agents that support processing CSYNC records SHOULD publicly   
  564    document the following minimum processing characteristics:              
  566       The fact that they support CSYNC processing                          
  568       The Type Bit Map bits they support                                   
  570       The frequency with which they poll clients (which may also be        
  571       configurable by the client)                                          
  573       If they support the "immediate" flag                                 
  575       If they poll a child's single nameserver, a configured list of       
  576       nameservers, or all of the advertised nameservers when querying      
  577       records                                                              
  579       If they support SOA serial number caching to avoid issues with       
  580       regression and/or replay                                             
  582       Where errors for CSYNC processing are published                      
  584       If they support sending queries to a "hidden master"                 
  586 4.5.  Removal of the CSYNC Records                                         
  588    Children MAY remove the CSYNC record upon noticing that the parent      
  589    zone has published the required records, thus eliminating the need      
  590    for the parent to continually query for the CSYNC record and all        
  591    corresponding records.  By removing the CSYNC record from the child     
  592    zone, the parental agent will only need to perform the query for the    
  593    CSYNC record and can stop processing when it finds it missing.  This    
  594    will reduce resource usage by both the child and the parental agent.    
  602 Hardaker                     Standards Track                   [Page 11]   

  603 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  606 4.6.  Parent/Child/Grandchild Glue Synchronization                         
  608    When a child needs to publish a CSYNC record that synchronizes NS and   
  609    A/AAAA glue records and the NS record is actually pointing to a child   
  610    of the child (a grandchild of the parent), then it is critical that     
  611    the glue records in the child point to the proper real addresses        
  612    records published by the grandchild.  It is assumed that if a child     
  613    is using a grandchild's nameserver that they must be in careful         
  614    synchronization.  Specifically, this specification requires this to     
  615    be the case.                                                            
  617 5.  Security Considerations                                                
  619    This specification requires the use of DNSSEC in order to determine     
  620    that the data being updated was unmodified by third parties.            
  621    Parental agents implementing CSYNC processing MUST ensure all DNS       
  622    transactions are validated by DNSSEC as "secure".  Clients deploying    
  623    CSYNC MUST ensure their zones are signed, current and properly linked   
  624    to the parent zone with a DS record that points to an appropriate       
  625    DNSKEY of the child's zone.                                             
  627    This specification does not address how to perform bootstrapping        
  628    operations to get the required initial DNSSEC-secured operating         
  629    environment in place.  Additionally, this specification was not         
  630    designed to synchronize DNSSEC security records, such as DS pointers,   
  631    or the CSYNC record itself.  Thus, implementations of this protocol     
  632    MUST NOT use it to synchronize DS records, DNSKEY materials, CDS        
  633    records, CDNSKEY records, or CSYNC records.  Similarly, future          
  634    documents extending this protocol MUST NOT offer the ability to         
  635    synchronize DS, DNSKEY materials, CDS records, CDNSKEY records, or      
  636    CSYNC records.  For such a solution, please see the complimentary       
  637    solution [RFC7344] for maintaining security delegation information.     
  639    To ensure that an older CSYNC record making use of the soaminimum       
  640    flag cannot be replayed to revert values, the SOA serial number MUST    
  641    NOT be incremented by more than 2^16 during the lifetime of the         
  642    signature window of the associated RRSIGs signing the SOA and CSYNC     
  643    records.  Note that this is independent of whether or not the           
  644    increment causes the 2^32 bit serial number field to wrap.              
  646 6.  IANA Considerations                                                    
  648    This document defines a new DNS Resource Record Type, named "CSYNC".    
  649    The IANA has assigned a code point from the "Resource Record (RR)       
  650    TYPEs" sub-registry of the "Domain Name System (DNS) Parameters"        
  651    registry (http://www.iana.org/assignments/dns-parameters) for this      
  652    record.                                                                 
  657 Hardaker                     Standards Track                   [Page 12]   

  658 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  661      TYPE    Value    Meaning                           Reference          
  662      -----   ------   --------------------------        -----------        
  663      CSYNC   62       Child-to-Parent Synchronization   [RFC7477]          
  665    The IANA has created and maintains a sub-registry (the "Child           
  666    Synchronization (CSYNC) Flags" registry) of the "Domain Name System     
  667    (DNS) Parameters" registry.  The initial values for this registry are   
  668    below.                                                                  
  670    A "Standards Action" [RFC5226] is required for the assignment of new    
  671    flag value.                                                             
  673    This registry holds a set of single-bit "Flags" for use in the CSYNC    
  674    record within the 16-bit Flags field.  Thus, a maximum of 16 flags      
  675    may be defined.                                                         
  677    The initial assignments in this registry are:                           
  679      Bit      Flag        Description               Reference              
  680      ----     ------      -------------             -----------            
  681      Bit 0    immediate   Immediately process this  [RFC7477],             
  682                           CSYNC record.             Section 3              
  684      Bit 1    soaminimum  Require a SOA serial      [RFC7477],             
  685                           number greater than the   Section        
  686                           one specified.                                   
  688 7.  References                                                             
  690 7.1.  Normative References                                                 
  692    [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,   
  693               August 1996, <http://www.rfc-editor.org/info/rfc1982>.       
  695    [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate          
  696               Requirement Levels", BCP 14, RFC 2119, March 1997,           
  697               <http://www.rfc-editor.org/info/rfc2119>.                    
  699    [RFC3597]  Gustafsson, A., "Handling of Unknown DNS Resource Record     
  700               (RR) Types", RFC 3597, September 2003,                       
  701               <http://www.rfc-editor.org/info/rfc3597>.                    
  703    [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and S.      
  704               Rose, "Resource Records for the DNS Security Extensions",    
  705               RFC 4034, March 2005,                                        
  706               <http://www.rfc-editor.org/info/rfc4034>.                    
  712 Hardaker                     Standards Track                   [Page 13]   

  713 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  716 7.2.  Informative References                                               
  718    [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",   
  719               STD 13, RFC 1034, November 1987,                             
  720               <http://www.rfc-editor.org/info/rfc1034>.                    
  722    [RFC1035]  Mockapetris, P., "Domain names - implementation and          
  723               specification", STD 13, RFC 1035, November 1987,             
  724               <http://www.rfc-editor.org/info/rfc1035>.                    
  726    [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.      
  727               Rose, "DNS Security Introduction and Requirements", RFC      
  728               4033, March 2005,                                            
  729               <http://www.rfc-editor.org/info/rfc4033>.                    
  731    [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and S.      
  732               Rose, "Protocol Modifications for the DNS Security           
  733               Extensions", RFC 4035, March 2005,                           
  734               <http://www.rfc-editor.org/info/rfc4035>.                    
  736    [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an     
  737               IANA Considerations Section in RFCs", BCP 26, RFC 5226,      
  738               May 2008, <http://www.rfc-editor.org/info/rfc5226>.          
  740    [RFC7344]  Kumari, W., Gudmundsson, O., and G. Barwood, "Automating     
  741               DNSSEC Delegation Trust Maintenance", RFC 7344, September    
  742               2014, <http://www.rfc-editor.org/info/rfc7344>.              
  767 Hardaker                     Standards Track                   [Page 14]   

  768 RFC 7477         Child-to-Parent Synchronization in DNS       March 2015   
  771 Acknowledgments                                                            
  773    A thank you goes out to Warren Kumari and Olafur Gudmundsson, whose     
  774    work on the CDS record type helped inspire the work in this document,   
  775    as well as the definition for the "parental agent" definition and       
  776    significant contributions to the text.  A thank you also goes out to    
  777    Ed Lewis, with whom the author held many conversations about the        
  778    issues surrounding parent/child relationships and synchronization.      
  779    Much of the work in this document is derived from the careful           
  780    existing analysis of these three esteemed colleagues.  Thank you to     
  781    the following people who have contributed text or detailed reviews to   
  782    the document (in no particular order): Matthijs Mekking, Petr Spacek,   
  783    JINMEI Tatuya, Pete Resnick, Joel Jaeggli, Brian Haberman, Warren       
  784    Kumari, Adrian Farrel, Alia Atlas, Barry Leiba, Richard Barnes,         
  785    Stephen Farrell, and Ted Lemon.  Lastly, the DNSOP WG chairs Tim        
  786    Wicinski and Suzanne Woolf have been a tremendous help in getting       
  787    this document moving forward to publication.                            
  789    A special thanks goes to Roy Arends, for taking the "bite out of that   
  790    hamburger" challenge while discussing this document.                    
  792    A similar project, independently designed and developed, was            
  793    conducted by ep.net called "Child Activated DNS Refresh".               
  795 Author's Address                                                           
  797    Wes Hardaker                                                            
  798    Parsons, Inc.                                                           
  799    P.O. Box 382                                                            
  800    Davis, CA  95617                                                        
  801    US                                                                      
  803    Phone: +1 530 792 1913                                                  
  804    EMail: ietf@hardakers.net                                               
  822 Hardaker                     Standards Track                   [Page 15]   
line-175 Donald Eastlake 3rd(Editorial Erratum #4307) [Verified]
based on outdated version
nonpunishable data
It should say:
nonpunblishable data

confusing typo, confirmed with author.