MORE INFORMATION
Definition of a Zone Transfer: A Zone Transfer is the term used to refer to
the process by which the contents of a DNS Zone file are copied from a
primary DNS server to a secondary DNS server.
A Zone transfer will occur during any of the following scenarios:
- When starting the DNS Service on the secondary DNS server.
- When the refresh time expires.
- When changes are saved to the Primary Zone file and there is a Notify
List.
Zone Transfers are always initiated by the secondary DNS server. The
primary DNS server simply answers the request for a Zone Transfer.
The following Network Monitor Capture sequence shows the process when
either the DNS Service is started on the secondary DNS server or the
refresh time expires:
Frame 1: The secondary DNS server - JH40PS - requests the SOA record from
the primary DNS server - SERVER - for Zone DOMAIN.COM. Note DNS Question
Type.
JH40PS SERVER DNS 0x4000:Std Qry for domain.com. of type SOA on class
INET addr.
DNS: 0x4000:Std Qry for domain.com. of type SOA on class INET addr.
DNS: Query Identifier = 16384 (0x4000)
DNS: DNS Flags = Query, OpCode - Std Qry, RCode - No error
DNS: 0............... = Query
DNS: .0000........... = Standard Query
DNS: .....0.......... = Server not authority for domain
DNS: ......0......... = Message complete
DNS: .......0........ = Iterative query desired
DNS: ........0....... = No recursive queries
DNS: .........000.... = Reserved
DNS: ............0000 = No error
DNS: Question Entry Count = 1 (0x1)
DNS: Answer Entry Count = 0 (0x0)
DNS: Name Server Count = 0 (0x0)
DNS: Additional Records Count = 0 (0x0)
DNS: Question Section: domain.com. of type SOA on class INET addr.
DNS: Question Name: domain.com.
DNS: Question Type = Start of zone of authority
DNS: Question Class = Internet address class
Frame 2: The primary DNS server responds with the contents of the SOA
record in the Answer Section.
SERVER JH40PS DNS 0x4000:Std Qry Resp. for domain.com. of type SOA on
class INET addr.
DNS: 0x4000:Std Qry Resp. for domain.com. of type SOA on class INET addr.
DNS: Query Identifier = 16384 (0x4000)
DNS: DNS Flags = Response, OpCode - Std Qry, AA RA Bits Set, RCode - No
error
DNS: 1............... = Response
DNS: .0000........... = Standard Query
DNS: .....1.......... = Server authority for domain
DNS: ......0......... = Message complete
DNS: .......0........ = Iterative query desired
DNS: ........1....... = Recursive queries supported by server
DNS: .........000.... = Reserved
DNS: ............0000 = No error
DNS: Question Entry Count = 1 (0x1)
DNS: Answer Entry Count = 1 (0x1)
DNS: Name Server Count = 0 (0x0)
DNS: Additional Records Count = 0 (0x0)
DNS: Question Section: domain.com. of type SOA on class INET addr.
DNS: Question Name: domain.com.
DNS: Question Type = Start of zone of authority
DNS: Question Class = Internet address class
DNS: Answer section: domain.com. of type SOA on class INET addr.
DNS: Resource Name: domain.com.
DNS: Resource Type = Start of zone of authority
DNS: Resource Class = Internet address class
DNS: Time To Live = 86400 (0x15180)
DNS: Resource Data Length = 41 (0x29)
DNS: Primary Name Server: server.domain.com.
DNS: Responsible Authorative Mailbox: administrator.domain.com.
DNS: Version number = 26 (0x1A)
DNS: Refresh Interval = 300 (0x12C)
DNS: Retry interval = 120 (0x78)
DNS: Expiration Limit = 600 (0x258)
DNS: Minimum TTL = 86400 (0x15180)
Frame 3: Having compared the version number (serial number) and found it to
be different than its current version number, the secondary DNS server now
requests a Zone Transfer. Note the Question Type in the DNS Question
Section.
JH40PS SERVER DNS 0x0:Std Qry for domain.com. of type Req. for zn
Xfer on class INET addr.
DNS: 0x0:Std Qry for domain.com. of type Req. for zn Xfer on class INET
addr.
DNS: TCP Length = 31 (0x1F)
DNS: Query Identifier = 0 (0x0)
DNS: DNS Flags = Query, OpCode - Std Qry, RCode - No error
DNS: 0............... = Query
DNS: .0000........... = Standard Query
DNS: .....0.......... = Server not authority for domain
DNS: ......0......... = Message complete
DNS: .......0........ = Iterative query desired
DNS: ........0....... = No recursive queries
DNS: .........000.... = Reserved
DNS: ............0000 = No error
DNS: Question Entry Count = 1 (0x1)
DNS: Answer Entry Count = 0 (0x0)
DNS: Name Server Count = 0 (0x0)
DNS: Additional Records Count = 0 (0x0)
DNS: Question Section: domain.com. of type Req. for zn Xfer on class
INET addr.
DNS: Question Name: domain.com.
DNS: Question Type = Request for zone transfer
DNS: Question Class = Internet address class
DNS: Frame Padding
Frame 4: The primary DNS server complies with the request for a Zone
Transfer. The entire contents of the Zone file are transferred in the DNS
Answer section.
SERVER JH40PS DNS 0x0:Std Qry Resp. for domain.com. of type SOA on
class INET addr.
DNS: 0x0:Std Qry Resp. for domain.com. of type SOA on class INET addr.
DNS: TCP Length = 445 (0x1BD)
DNS: Query Identifier = 0 (0x0)
DNS: DNS Flags = Response, OpCode - Std Qry, RA Bits Set, RCode - No
error
DNS: 1............... = Response
DNS: .0000........... = Standard Query
DNS: .....0.......... = Server not authority for domain
DNS: ......0......... = Message complete
DNS: .......0........ = Iterative query desired
DNS: ........1....... = Recursive queries supported by server
DNS: .........000.... = Reserved
DNS: ............0000 = No error
DNS: Question Entry Count = 1 (0x1)
DNS: Answer Entry Count = 16 (0x10)
DNS: Name Server Count = 0 (0x0)
DNS: Additional Records Count = 0 (0x0)
DNS: Question Section: domain.com. of type Req. for zn Xfer on class
INET addr.
DNS: Question Name: domain.com.
DNS: Question Type = Request for zone transfer
DNS: Question Class = Internet address class
DNS: Answer section: . of type SOA on class INET addr.(16 records
present)
DNS: Resource Record: domain.com. of type SOA on class INET addr.
DNS: Resource Name: domain.com.
DNS: Resource Type = Start of zone of authority
DNS: Resource Class = Internet address class
DNS: Time To Live = 86400 (0x15180)
DNS: Resource Data Length = 41 (0x29)
DNS: Primary Name Server: server.domain.com.
DNS: Responsible Authorative Mailbox: administrator.domain.com.
DNS: Version number = 26 (0x1A)
DNS: Refresh Interval = 300 (0x12C)
DNS: Retry interval = 120 (0x78)
DNS: Expiration Limit = 600 (0x258)
DNS: Minimum TTL = 86400 (0x15180)
DNS: Resource Record: domain.com. of type Host Addr on class INET
addr.
DNS: Resource Name: domain.com.
DNS: Resource Type = Host Address
DNS: Resource Class = Internet address class
DNS: Time To Live = 86400 (0x15180)
DNS: Resource Data Length = 4 (0x4)
DNS: IP address = 130.0.10.150
DNS: Resource Record: domain.com. of type Auth. NS on class INET
addr.
DNS: Resource Name: domain.com.
DNS: Resource Type = Authoritative Name Server
DNS: Resource Class = Internet address class
DNS: Time To Live = 86400 (0x15180)
DNS: Resource Data Length = 10 (0xA)
DNS: Authoritative Name Server: server.domain.com.
DNS: Resource Record: Dell.domain.com. of type Host Addr on class
INET addr.
DNS: Resource Name: Dell.domain.com.
DNS: Resource Type = Host Address
DNS: Resource Class = Internet address class
DNS: Time To Live = 86400 (0x15180)
DNS: Resource Data Length = 4 (0x4)
DNS: IP address = 130.0.10.30
DNS: Resource Record: JH40PS.domain.com. of type Host Addr on
class INET addr.
DNS: Resource Name: JH40PS.domain.com.
DNS: Resource Type = Host Address
DNS: Resource Class = Internet address class
DNS: Time To Live = 86400 (0x15180)
DNS: Resource Data Length = 4 (0x4)
DNS: IP address = 130.0.10.155
If changes are made to the Zone file and there are entries in the Notify
List, the following sequence will occur before the regular Zone Transfer
sequence as outlined above.
Frame A: In this frame, a change has been made to the Zone file. Because
JH40PS is on the Notify List, the primary DNS server sends this frame to
notify the secondary DNS server that a change has occurred and that the
secondary DNS server should query the SOA resource record.
SERVER JH40PS DNS 0x0:Std Qry for domain.com. of type SOA on class
INET addr.
DNS: 0x0:Std Qry for domain.com. of type SOA on class INET addr.
DNS: Query Identifier = 0 (0x0)
DNS: DNS Flags = Query, OpCode - Rsrvd, AA Bits Set, RCode - No error
DNS: 0............... = Query
DNS: .0100........... = Reserved
DNS: .....1.......... = Server authority for domain
DNS: ......0......... = Message complete
DNS: .......0........ = Iterative query desired
DNS: ........0....... = No recursive queries
DNS: .........000.... = Reserved
DNS: ............0000 = No error
DNS: Question Entry Count = 1 (0x1)
DNS: Answer Entry Count = 0 (0x0)
DNS: Name Server Count = 0 (0x0)
DNS: Additional Records Count = 0 (0x0)
DNS: Question Section: domain.com. of type SOA on class INET addr.
DNS: Question Name: domain.com.
DNS: Question Type = Start of zone of authority
DNS: Question Class = Internet address class
Frame B: The secondary DNS server acknowledges the receipt of Frame 1.
JH40PS SERVER DNS 0x0:Std Qry Resp.
DNS: 0x0:Std Qry Resp.
DNS: Query Identifier = 0 (0x0)
DNS: DNS Flags = Response, OpCode - Rsrvd, AA Bits Set, RCode - No
error
DNS: 1............... = Response
DNS: .0100........... = Reserved
DNS: .....1.......... = Server authority for domain
DNS: ......0......... = Message complete
DNS: .......0........ = Iterative query desired
DNS: ........0....... = No recursive queries
DNS: .........000.... = Reserved
DNS: ............0000 = No error
DNS: Question Entry Count = 1 (0x1)
DNS: Answer Entry Count = 0 (0x0)
DNS: Name Server Count = 0 (0x0)
DNS: Additional Records Count = 0 (0x0)
DNS: Question Section: domain.com. of type SOA on class INET addr.
DNS: Question Name: domain.com.
DNS: Question Type = Start of zone of authority
DNS: Question Class = Internet address class
Immediately following this response, the Zone Transfer process begins as in
Frame 1 in the first capture sequence above.