6. IANA Considerations
6. IANA Considerations
This document defines a number of registries that are managed by the Internet Assigned Numbers Authority (IANA). This section describes these registries and the policies for allocating values from them.
6.1. Security Models
The SNMP architecture allows for multiple Security Models. Each Security Model is identified by a unique securityModel value. The allocation of securityModel values is managed by IANA.
The securityModel value is an INTEGER in the range 0 to 2147483647.
Values are allocated as follows:
| Value Range | Allocation Policy | Description |
|---|---|---|
| 0 | Reserved | Does not identify any security model |
| 1 | Standards Action | SNMPv1 security model |
| 2 | Standards Action | SNMPv2c security model |
| 3 | Standards Action | User-based Security Model (USM) |
| 4-255 | Standards Action | Reserved for standards-track Security Models |
| 256+ | First Come First Served | Enterprise-specific Security Models |
Standards Action means that values in this range can only be assigned through the publication of an RFC approved by the IESG.
First Come First Served means that values in this range are allocated to enterprises based on their enterprise ID. The formula is:
securityModel = (enterpriseID * 256) + security model within enterprise
For example, if enterprise ID 1 defines a security model, and this is their fourth security model, the value would be:
securityModel = (1 * 256) + 4 = 260
Current allocations:
- 0: Reserved (any)
- 1: SNMPv1 (RFC 3584)
- 2: SNMPv2c (RFC 3584)
- 3: User-based Security Model (USM) (RFC 3414)
6.2. Message Processing Models
The SNMP architecture allows for multiple Message Processing Models. Each Message Processing Model is identified by a unique messageProcessingModel value. The allocation of messageProcessingModel values is managed by IANA.
The messageProcessingModel value is an INTEGER in the range 0 to 2147483647.
Values are allocated as follows:
| Value Range | Allocation Policy | Description |
|---|---|---|
| 0 | Standards Action | SNMPv1 message processing |
| 1 | Standards Action | SNMPv2c message processing |
| 2 | Standards Action | SNMPv2u (historic, not used) |
| 3 | Standards Action | SNMPv3 message processing |
| 4-255 | Standards Action | Reserved for standards-track Message Processing Models |
| 256+ | First Come First Served | Enterprise-specific Message Processing Models |
Standards Action means that values in this range can only be assigned through the publication of an RFC approved by the IESG.
First Come First Served means that values in this range are allocated to enterprises based on their enterprise ID. The formula is:
messageProcessingModel = (enterpriseID * 256) + model within enterprise
Current allocations:
- 0: SNMPv1 (RFC 3584)
- 1: SNMPv2c (RFC 3584)
- 2: SNMPv2u (historic)
- 3: SNMPv3 (RFC 3412)
6.3. SnmpEngineID Formats
The snmpEngineID is used to uniquely identify an SNMP engine. To ensure global uniqueness, a specific format is recommended for snmpEngineID values.
The snmpEngineID is an OCTET STRING of 5 to 32 octets.
The first four octets are defined by the following:
Octet 1-4: Enterprise ID
The first bit indicates the format of the remaining octets:
-
Bit 1 = 0: The format is:
Octets: [1-4: Enterprise ID] [5: format] [6-32: format-specific] -
Bit 1 = 1: The format is:
Octets: [1-4: IANA Enterprise Number] [5-32: enterprise-specific]
For snmpEngineID values where the first bit of the first octet is 0, the fifth octet is a format identifier. The following formats are currently defined:
| Format Value | Description |
|---|---|
| 0 | Reserved, unused |
| 1 | IPv4 address (4 octets) |
| 2 | IPv6 address (16 octets) |
| 3 | MAC address (6 octets) |
| 4 | Administratively assigned text (0-27 octets) |
| 5 | Administratively assigned octets (0-27 octets) |
| 6-127 | Reserved, unused |
| 128-255 | Enterprise-specific formats |
Example formats:
-
Format 1 (IPv4 address):
[0-3: Enterprise ID (bit 1 = 0)]
[4: 0x01]
[5-8: IPv4 address] -
Format 2 (IPv6 address):
[0-3: Enterprise ID (bit 1 = 0)]
[4: 0x02]
[5-20: IPv6 address] -
Format 3 (MAC address):
[0-3: Enterprise ID (bit 1 = 0)]
[4: 0x03]
[5-10: MAC address] -
Format 4 (Text):
[0-3: Enterprise ID (bit 1 = 0)]
[4: 0x04]
[5-31: Administratively assigned text] -
Format 5 (Octets):
[0-3: Enterprise ID (bit 1 = 0)]
[4: 0x05]
[5-31: Administratively assigned octets]
Requirements:
- The snmpEngineID value must be unique within the administrative domain
- The snmpEngineID value must remain constant across reboots
- The snmpEngineID value should be stored in non-volatile storage
- The snmpEngineID value must not be all zeros
- The snmpEngineID value must not be all
0xFF(all bits set) - The snmpEngineID value must not be empty (zero length)
Recommendations:
- When using format 1, 2, or 3, the address should be one that is permanently assigned to the device
- When using format 4 or 5, the value should be administratively assigned in a way that ensures uniqueness
- If a device has multiple SNMP engines, each must have a unique snmpEngineID
IANA Actions:
IANA maintains a registry of snmpEngineID format values (format identifier octet). New format values in the range 6-127 require Standards Action. Format values in the range 128-255 are available for enterprise-specific use without registration.