DNS.Message.EDNS0.Option.ECS (DNS v0.5.0)

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EDNS0.Option.ECS RFC7871

Option Format

This protocol uses an EDNS0 [RFC6891] option to include client address information in DNS messages. The option is structured as follows:

              +0 (MSB)                            +1 (LSB)
    +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
0: |                          OPTION-CODE                          |
    +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
2: |                         OPTION-LENGTH                         |
    +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
4: |                            FAMILY                             |
    +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
6: |     SOURCE PREFIX-LENGTH      |     SCOPE PREFIX-LENGTH       |
    +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
8: |                           ADDRESS...                          /
    +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

o (Defined in [RFC6891]) OPTION-CODE, 2 octets, for ECS is 8 (0x00

0x08).

o (Defined in [RFC6891]) OPTION-LENGTH, 2 octets, contains the

length of the payload (everything after OPTION-LENGTH) in octets.

o FAMILY, 2 octets, indicates the family of the address contained in

the option, using address family codes as assigned by IANA in
Address Family Numbers [Address_Family_Numbers].

The format of the address part depends on the value of FAMILY. This document only defines the format for FAMILY 1 (IPv4) and FAMILY 2 (IPv6), which are as follows:

o SOURCE PREFIX-LENGTH, an unsigned octet representing the leftmost

number of significant bits of ADDRESS to be used for the lookup.
In responses, it mirrors the same value as in the queries.

o SCOPE PREFIX-LENGTH, an unsigned octet representing the leftmost

number of significant bits of ADDRESS that the response covers.
In queries, it MUST be set to 0.

o ADDRESS, variable number of octets, contains either an IPv4 or

IPv6 address, depending on FAMILY, which MUST be truncated to the
number of bits indicated by the SOURCE PREFIX-LENGTH field,
padding with 0 bits to pad to the end of the last octet needed.

o A server receiving an ECS option that uses either too few or too

many ADDRESS octets, or that has non-zero ADDRESS bits set beyond
SOURCE PREFIX-LENGTH, SHOULD return FORMERR to reject the packet,
as a signal to the software developer making the request to fix
their implementation.

All fields are in network byte order ("big-endian", per [RFC1700], Data Notation).

Summary

Types

t()

Functions

from_iodata(arg)
new(arg)
to_raw(arg)

Types

t()

@type t() :: %DNS.Message.EDNS0.Option.ECS{
  code: DNS.Message.EDNS0.OptionCode.t(),
  data:
    {client_subnet :: :inet.ip_address(), source_prefix :: 0..128,
     scope_prefix :: 0..128},
  length: 0..65535
}

Functions

from_iodata(arg)

new(arg)

@spec new({:inet.ip4_address(), 0..32, 0..32}) :: t()
@spec new({:inet.ip6_address(), 0..128, 0..128}) :: t()

to_raw(arg)

@spec to_raw({:inet.ip4_address(), 0..32, 0..32}) :: binary()
@spec to_raw({:inet.ip6_address(), 0..128, 0..128}) :: binary()