The ATTRIBUTE keyword

Syntax

ATTRIBUTE <name> <number> <type> [<flags>]

Description

The ATTRIBUTE keyword defines a name, number, and data type mapping.

<name>: The name of the attribute. The name can contain alphanumeric characters, -, and _. The name should be short and descriptive.

As the names are hierarchical, the name is scoped to its parent. So the name Counter can mean different things, depending on its context.
<number>: The number of the attribute. Numbers can be specified as decimal (19), or as hex (0xffee).

Numbers can also be specified as object identifiers (OIDs), 26.1.9, or as partial OIDs (.14).

There are a number of complex rules and interpretations of OID values which are difficult to clearly document using simple examples. This complex behavior is only needed for rare situations. In short, if you are creating complex protocol dictionaries, you need to understand those protocols before creating the dictionaries. On the other hand, if you are creating simple protocol dictionaries, there is no need to understand any complex rules around the use of OIDs.
<type>: A data type

A few data types can be marked up as being fixed size, by adding an "array-style" suffix, such as with octets[3]. See below for details.
<flags>: The flag field is optional, and is usually protocol-specific. See the FLAGS page for definitions of common flags.

Please see the protocol dictionaries for examples of these flags. Only the flags which are used in a protocol dictionary are valid, and those flags are only valid for that protocol dictionary.

The old-style RADIUS syntax of specifying a vendor name in the flags field is not supported.

Common flags and meanings

Name Description

Name	Description
`array`	For fixed-size types, declare that the contents of the packet can have an array of this value.
`clone=<ref>`	For `tlv` or 'struct' types, clone (or copy) child definitions from another attribute of the same type
`concat`	For `octet` data types, the server will automatically split/merge values into attributes.
`counter`	For numeric data types, treat the values as SNMP-style counters, which can be automatically added.
`enum=<ref>`	For "leaf" types, copy VALUEs from an ENUM or other attribute.
`internal`	This attribute is internal to the server, and will never be sent "on the wire"
`ref=<ref>`	For `group` types, the referenced attributes will be allowed in the group
`secret`	The server will not print `secret` values in debug mode, and in many other situations.

array

For fixed-size types, declare that the contents of the packet can have an array of this value.

clone=<ref>

For tlv or 'struct' types, clone (or copy) child definitions from another attribute of the same type

concat

For octet data types, the server will automatically split/merge values into attributes.

counter

For numeric data types, treat the values as SNMP-style counters, which can be automatically added.

enum=<ref>

For "leaf" types, copy VALUEs from an ENUM or other attribute.

internal

This attribute is internal to the server, and will never be sent "on the wire"

ref=<ref>

For group types, the referenced attributes will be allowed in the group

secret

The server will not print secret values in debug mode, and in many other situations.

The <ref> field in the examples above is an attribute references such as Foo, or Foo.Bar, or @dhcpv4.foo.bar. All <ref> fields use the same syntax.

If the ref begins with @ the ref will be treated as a "foreign" reference to another protocol. The first component will be used as the protocol name e.g. ref=@RADIUS.

If the ref begins with . the ref will be treated as relative to the current attribute, else resolution will begin from the root of the current dictionary.

Multiple consecutive . can be used to traverse up the attribute hierarchy from the current attribute.

Examples

ATTRIBUTE Foo 1 string[3]
ATTRIBUTE Bar 2 octets
ATTRIBUTE baz 3 ipv4addr

Enum

In some cases, attributes need to reuse the same set of VALUE statements. The enum=… flag allows an attribute to copy enumerated vl

The enum flag can only be used for "leaf" data types. i.e. ones which can contain a VALUE.

Enum Examples

ATTRIBUTE Foo 1 integer
VALUE Zero Foo 0

ATTRIBUTE Bar 2 integer enum=Foo

The result of the above dictionary is that the Bar attribute also has VALUE defined, with name Zero.

Clone

In some cases, structured attributes have different parents, but identical children. The clone=… flag allows an attribute to copy or "clone" the children of another attribute.

The clone flag can only be used for data types tlv and struct.

Clone Examples

ATTRIBUTE Foo 1 tlv
ATTRIBUTE Bar 1.1 ipaddr
ATTRIBUTE Baz 2 tlv clone=Foo

The result of the above dictionary is that the Baz attribute also has child attribute, of name Bar.

Ref

In some cases, attributes can "group" other attributes without adding a new hierarchy. The ref=… flag allows a grouped attribute to reference another attribute. The grouped attribute can then contain the referenced attributes, as if those other attributes were members of the group.

If ref is not given for an attribute of type group then the reference is assumed to be to the "root" of the current protocol dictionary.

The ref flag can only be used for the data type group. The referenced attribute must be of data type group or tlv. 613 816 8331 == Fixed Size Data types

The following data types can be marked up as having fixed size, by using an array suffix, e.g. octets[14].

Fixed Size types and meanings

Type Description

Type	Description
`octets[n]`	Declare that this attribute uses `n` bytes of `octets` data
`string[n]`	Declare that this attribute uses `n` bytes of `string` data
`struct[n]`	Declare that this structure uses `n` bytes for itself, including all child MEMBERs

octets[n]

Declare that this attribute uses n bytes of octets data

string[n]

Declare that this attribute uses n bytes of string data

struct[n]

Declare that this structure uses n bytes for itself, including all child MEMBERs