dhcpkit.ipv6.extensions.client_fqdn module

Implementation of the Client FQDN option as specified in RFC 4704.

class dhcpkit.ipv6.extensions.client_fqdn.ClientFQDNOption(flags: int = 0, domain_name: str = None)

Bases: dhcpkit.ipv6.options.Option

To update the IPv6-address-to-FQDN mapping, a DHCPv6 server needs to know the FQDN of the client for the addresses for the client’s IA_NA bindings. To allow the client to convey its FQDN to the server, this document defines a new DHCPv6 option called “Client FQDN”. The Client FQDN option also contains Flags that DHCPv6 clients and servers use to negotiate who does which updates.

The code for this option is 39. Its minimum length is 1 octet.

The format of the DHCPv6 Client FQDN option is shown below:

 0                   1                   2                   3
 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          OPTION_FQDN          |         option-len            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   flags       |                                               |
+-+-+-+-+-+-+-+-+                                               |
.                                                               .
.                          domain-name                          .
.                                                               .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code

OPTION_CLIENT_FQDN (39).

option-len

1 + length of domain name.

flags

flag bits used between client and server to negotiate who performs which updates.

domain-name

the partial or fully qualified domain name (with length option-len - 1).

The Client FQDN option MUST only appear in a message’s options field and applies to all addresses for all IA_NA bindings in the transaction.

4.1. The Flags Field

The format of the Flags field is:

 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|  MBZ    |N|O|S|
+-+-+-+-+-+-+-+-+

The “S” bit indicates whether the server SHOULD or SHOULD NOT perform the AAAA RR (FQDN-to-address) DNS updates. A client sets the bit to 0 to indicate that the server SHOULD NOT perform the updates and 1 to indicate that the server SHOULD perform the updates. The state of the bit in the reply from the server indicates the action to be taken by the server; if it is 1, the server has taken responsibility for AAAA RR updates for the FQDN.

The “O” bit indicates whether the server has overridden the client’s preference for the “S” bit. A client MUST set this bit to 0. A server MUST set this bit to 1 if the “S” bit in its reply to the client does not match the “S” bit received from the client.

The “N” bit indicates whether the server SHOULD NOT perform any DNS updates. A client sets this bit to 0 to request that the server SHOULD perform updates (the PTR RR and possibly the AAAA RR based on the “S” bit) or to 1 to request that the server SHOULD NOT perform any DNS updates. A server sets the “N” bit to indicate whether the server SHALL (0) or SHALL NOT (1) perform DNS updates. If the “N” bit is 1, the “S” bit MUST be 0.

The remaining bits in the Flags field are reserved for future assignment. DHCPv6 clients and servers that send the Client FQDN option MUST clear the MBZ bits, and they MUST ignore these bits.

4.2. The Domain Name Field

The Domain Name part of the option carries all or part of the FQDN of a DHCPv6 client. The data in the Domain Name field MUST be encoded as described in Section 8 of [5]. In order to determine whether the FQDN has changed between message exchanges, the client and server MUST NOT alter the Domain Name field contents unless the FQDN has actually changed.

A client MAY be configured with a fully qualified domain name or with a partial name that is not fully qualified. If a client knows only part of its name, it MAY send a name that is not fully qualified, indicating that it knows part of the name but does not necessarily know the zone in which the name is to be embedded.

To send a fully qualified domain name, the Domain Name field is set to the DNS-encoded domain name including the terminating zero-length label. To send a partial name, the Domain Name field is set to the DNS-encoded domain name without the terminating zero-length label.

A client MAY also leave the Domain Name field empty if it desires the server to provide a name.

Servers SHOULD send the complete fully qualified domain name in Client FQDN options.

load_from(buffer: bytes, offset: int = 0, length: int = None) → int

Load the internal state of this object from the given buffer. The buffer may contain more data after the structured element is parsed. This data is ignored.

Parameters:

• buffer – The buffer to read data from
• offset – The offset in the buffer where to start reading
• length – The amount of data we are allowed to read from the buffer

Returns:

The number of bytes used from the buffer

no_server_dns_update

Extract the N flag

Returns:Whether the N flag is set

option_type = 39

save() → Union

Save the internal state of this object as a buffer.

Returns:The buffer with the data from this element

server_aaaa_override

Extract the O flag

Returns:Whether the O flag is set

server_aaaa_update

Extract the S flag

Returns:Whether the S flag is set

validate()

Validate that the contents of this object conform to protocol specs.