Draft SNMPv2 Administrative Model Dec 92 Administrative Model | for version 2 of the | Simple Network Management Protocol (SNMPv2) | Sun Dec 6 16:26:43 1992 | James R. (Chuck) Davin Bellcore davin@thumper.bellcore.com James M. Galvin Trusted Information Systems, Inc. galvin@tis.com Keith McCloghrie Hughes LAN Systems kzm@hls.com Status of this Memo This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet Drafts as reference material or to cite them other than as a "work in progress". Expires June 6, 1993 [Page 1] Draft SNMPv2 Administrative Model Dec 92 1. Introduction A network management system contains: several (potentially many) nodes, each with a processing entity, termed an agent, which has access to management instrumentation; at least one management station; and, a management protocol, used to convey management information between the agents and management stations. Operations of the protocol are carried out under an administrative framework which defines both authentication and authorization policies. Network management stations execute management applications which monitor and control network elements. Network elements are devices such as hosts, routers, terminal servers, etc., which are monitored and controlled through access to their management information. It is the purpose of this document, the Administrative Model | for SNMPv2, to define how the administrative framework is | applied to realize effective network management in a variety | of configurations and environments. | The model described here entails the use of distinct identities for peers that exchange SNMPv2 messages. | Thus, it represents a departure from the community-based | administrative model of the original SNMP [1]. | By unambiguously identifying the source and intended recipient of each SNMPv2 message, this new strategy improves upon the | historical | community scheme both by supporting a more convenient access control model and allowing for effective use of asymmetric (public key) security protocols in the future. 1.1. A Note on Terminology For the purpose of exposition, the original Internet-standard + Network Management Framework, as described in RFCs 1155, 1157, + and 1212, is termed the SNMP version 1 framework (SNMPv1). + The current framework is termed the SNMP version 2 framework + (SNMPv2). + Expires June 6, 1993 [Page 2] Draft SNMPv2 Administrative Model Dec 92 2. Elements of the Model 2.1. SNMPv2 Party A SNMPv2 party is a conceptual, virtual execution context | whose | operation is restricted (for security or other purposes) to an administratively defined subset of all possible operations of a particular SNMPv2 entity (see Section 2.2). Whenever a | SNMPv2 entity processes a SNMPv2 message, it does so by acting | as a SNMPv2 party and is thereby restricted to the set of | operations defined | for that party. The set of possible operations specified for | a SNMPv2 | party may be overlapping or disjoint with respect to the sets of other SNMPv2 parties; it may also be a proper or improper | subset of all possible operations of the SNMPv2 entity. | Architecturally, each SNMPv2 party comprises | o a single, unique party identity, o a single authentication protocol and associated parameters by which all protocol messages originated by the party are authenticated as to origin and integrity, o a single privacy protocol and associated parameters by which all protocol messages received by the party are protected from disclosure, o a single MIB view (see Section 2.6) to which all | management operations performed by the party are applied, and o a logical network location at which the party executes, characterized by a transport protocol domain and Expires June 6, 1993 [Page 3] Draft SNMPv2 Administrative Model Dec 92 transport addressing information. Conceptually, each SNMPv2 party may be represented by an ASN.1 | value | with the following syntax: SnmpParty ::= SEQUENCE { - partyIdentity OBJECT IDENTIFIER, partyTDomain OBJECT IDENTIFIER, partyTAddr OCTET STRING, partyProxyFor OBJECT IDENTIFIER, partyMaxMessageSize INTEGER, partyAuthProtocol OBJECT IDENTIFIER, partyAuthClock INTEGER, partyAuthPrivate - OCTET STRING, partyAuthPublic OCTET STRING, partyAuthLifetime INTEGER, partyPrivProtocol OBJECT IDENTIFIER, partyPrivPrivate OCTET STRING, partyPrivPublic OCTET STRING } For each SnmpParty value that represents a SNMPv2 party, the | following | statements are true: o Its partyIdentity component is the party identity. o Its partyTDomain component is called the transport domain and indicates the kind of transport service by which the party receives network management traffic. An example of a transport domain is snmpUDPDomain (SNMPv2 over UDP, | Expires June 6, 1993 [Page 4] Draft SNMPv2 Administrative Model Dec 92 using SNMPv2 | parties). o Its partyTAddr component is called the transport addressing information and represents a transport service address by which the party receives network management traffic. o Its partyProxyFor component is called the proxied party | and represents the identity of a second SNMPv2 | party or other management entity with which interaction may be necessary to satisfy received management requests. In this context, the value noProxy signifies that the party responds to received management requests by entirely local mechanisms. o Its partyMaxMessageSize component is called the maximum message size and represents the length in octets of the | largest SNMPv2 message this party is | prepared to accept. o Its partyAuthProtocol component is called the authentication protocol and identifies a protocol and a mechanism by which all messages generated by the party are authenticated as to integrity and origin. In this context, the value noAuth signifies that messages generated by the party are not authenticated as to integrity and origin. o Its partyAuthClock component is called the authentication clock and represents a notion of the current time that is specific to the party. The significance of this component is specific to the authentication protocol. o - Its partyAuthPrivate component is called the private authentication key and represents any secret value needed to support the authentication protocol. The significance of this component is specific to the authentication protocol. o Its partyAuthPublic component is called the public authentication key and represents any public value that may be needed to support the authentication protocol. The significance of this component is specific to the Expires June 6, 1993 [Page 5] Draft SNMPv2 Administrative Model Dec 92 authentication protocol. o Its partyAuthLifetime component is called the lifetime and represents an administrative upper bound on acceptable delivery delay for protocol messages generated by the party. The significance of this component is specific to the authentication protocol. o Its partyPrivProtocol component is called the privacy protocol and identifies a protocol and a mechanism by which all protocol messages received by the party are protected from disclosure. In this context, the value noPriv signifies that messages received by the party are not protected from disclosure. o Its partyPrivPrivate component is called the private privacy key and represents any secret value needed to support the privacy protocol. The significance of this component is specific to the privacy protocol. o Its partyPrivPublic component is called the public privacy key and represents any public value that may be needed to support the privacy protocol. The significance of this component is specific to the privacy protocol. If, for all SNMPv2 parties realized by a SNMPv2 entity, the | authentication protocol is noAuth and the privacy protocol is noPriv, then that entity is called non-secure. | 2.2. SNMPv2 Entity A SNMPv2 entity is an actual process which performs network | management operations by generating and/or responding to | SNMPv2 protocol messages in the manner specified in [2]. When | a SNMPv2 entity is acting as a particular SNMPv2 party (see | Section 2.1), the | operation of that entity must be restricted to the subset of all possible operations that is administratively defined for that party. By definition, the operation of a SNMPv2 entity requires no | concurrency between processing of any single protocol message (by a particular SNMPv2 party) and processing of any other | protocol message (by a potentially different SNMPv2 party). | Expires June 6, 1993 [Page 6] Draft SNMPv2 Administrative Model Dec 92 Accordingly, implementation of a SNMPv2 entity to support more | than one party need not be | multi-threaded. However, there may be situations where implementors may choose to use multi-threading. Architecturally, every SNMPv2 entity maintains a local | database that represents all SNMPv2 parties known to it - | those whose operation is | realized locally, those whose operation is realized by proxy interactions with remote parties or devices, and those whose operation is realized by remote entities. In addition, every | SNMPv2 entity maintains a local database that represents an | access control policy (see Section 2.11) that defines the | access privileges accorded to known SNMPv2 parties. | 2.3. SNMPv2 Management Station A SNMPv2 management station is the operational role assumed by | a SNMPv2 party when it initiates SNMPv2 management operations | by the generation of appropriate SNMPv2 protocol messages or | when it receives and | processes trap notifications. Sometimes, the term SNMPv2 management station is applied to | partial implementations of the SNMPv2 (in graphics | workstations, for example) | that focus upon this operational role. Such partial implementations may provide for convenient, local invocation of management services, but they may provide little or no | support for performing SNMPv2 | management operations on behalf of remote protocol users. 2.4. SNMPv2 Agent A SNMPv2 agent is the operational role assumed by a SNMPv2 | party when it performs SNMPv2 management operations in | response to received SNMPv2 protocol messages such as those | generated by a SNMPv2 management station (see Section 2.3). | Sometimes, the term SNMPv2 agent is applied to partial | implementations of the SNMPv2 (in embedded systems, for | example) that focus upon this | operational role. Such partial implementations provide for | Expires June 6, 1993 [Page 7] Draft SNMPv2 Administrative Model Dec 92 realization of SNMPv2 management operations on behalf of | remote users | of management services, but they may provide little or no support for local invocation of such services. 2.5. View Subtree A view subtree is the set of all MIB object instances which have a common ASN.1 OBJECT IDENTIFIER prefix to their names. A view subtree is identified by the OBJECT IDENTIFIER value which is the longest OBJECT IDENTIFIER prefix common to all (potential) MIB object instances in that subtree. When the OBJECT IDENTIFIER prefix identifying a view subtree + is longer than the OBJECT IDENTIFIER of an object type defined + according to the SMI [3], then the use of such a view subtree + for access control has granularity at the object instance + level. Such granularity is considered beyond the scope of a + SNMPv2 entity acting in an agent role. As such, no + implementation of a SNMPv2 entity acting in an agent role is + required to support values of viewSubtree [6] which have more + sub-identifiers than is necessary to identify a particular + leaf object type. However, access control is used in + determining which SNMPv2 entities acting in a manager role + should receive trap notifications (Section 4.2.6 of [2]). As + such, agent implementors might wish to provide instance-level + granularity in order to allow a management station to use + fine-grain configuration of trap notifications. + 2.6. MIB View A MIB view is a subset of the set of all instances of all object types defined according to the SMI [3] (i.e., of | the universal set of all instances of all MIB objects), subject to the following constraints: o Each element of a MIB view is uniquely named by an ASN.1 OBJECT IDENTIFIER value. As such, identically named instances of a particular object type (e.g., in different agents) must be contained within different MIB views. That is, a particular object instance name resolves within a particular MIB view to at most one object instance. Expires June 6, 1993 [Page 8] Draft SNMPv2 Administrative Model Dec 92 o Every MIB view is defined as a collection of view subtrees. 2.7. SNMPv2 Management Communication | A SNMPv2 management communication is a communication from one | specified SNMPv2 party to a second specified SNMPv2 party | about management | information that is represented in the MIB view of the appropriate party. In particular, a SNMPv2 management | communication may be | o a query by the originating party about information in the MIB view of the addressed party (e.g., getRequest and getNextRequest), o an indicative assertion to the addressed party about information in the MIB view of the originating party | (e.g., Response or SNMPv2-Trap), or | o an imperative assertion by the originating party about information in the MIB view of the addressed party (e.g., setRequest). A management communication is represented by an ASN.1 value with the following syntax: | SnmpMgmtCom ::= [1] IMPLICIT SEQUENCE { - dstParty OBJECT IDENTIFIER, srcParty OBJECT IDENTIFIER, pdu PDUs } For each SnmpMgmtCom value that represents a SNMPv2 management | communication, the following statements are true: o Its dstParty component is called the destination and | identifies the SNMPv2 party to which the communication | is directed. Expires June 6, 1993 [Page 9] Draft SNMPv2 Administrative Model Dec 92 o Its srcParty component is called the source and | identifies the SNMPv2 party from which the | communication is originated. o Its pdu component has the form and significance | attributed to it in [2]. | 2.8. SNMPv2 Authenticated Management Communication A SNMPv2 authenticated management communication is a SNMPv2 | management communication (see Section 2.7) for which the | originating SNMPv2 party | is (possibly) reliably identified and for which the integrity of the transmission of the communication is (possibly) protected. An authenticated management communication is represented by an ASN.1 value with the following syntax: | SnmpAuthMsg ::= [1] IMPLICIT SEQUENCE { - authInfo ANY, - defined by authentication protocol authData SnmpMgmtCom } For each SnmpAuthMsg value that represents a SNMPv2 | authenticated | management communication, the following statements are true: o Its authInfo component is called the authentication information and represents information required in support of the authentication protocol used by the SNMPv2 | party originating the message. | The detailed significance of the authentication information is specific to the authentication protocol in use; it has no effect on the application semantics of the communication other than its use by the authentication protocol in determining whether the communication is authentic or not. o Its authData component is called the authentication data | and represents a SNMPv2 management | communication. Expires June 6, 1993 [Page 10] Draft SNMPv2 Administrative Model Dec 92 2.9. SNMPv2 Private Management Communication A SNMPv2 private management communication is a SNMPv2 | authenticated management communication (see Section 2.8) that | is (possibly) | protected from disclosure. A private management communication is represented by an ASN.1 value with the following syntax: | SnmpPrivMsg ::= [1] IMPLICIT SEQUENCE { - privDst OBJECT IDENTIFIER, privData [1] IMPLICIT OCTET STRING } For each SnmpPrivMsg value that represents a SNMPv2 private | management | communication, the following statements are true: o Its privDst component is called the privacy destination | and identifies the SNMPv2 party to which the | communication is directed. o Its privData component is called the privacy data and represents the (possibly encrypted) serialization | (according to the conventions of [5] and [2]) of a SNMPv2 | authenticated management communication (see Section 2.8). | Expires June 6, 1993 [Page 11] Draft SNMPv2 Administrative Model Dec 92 2.10. SNMPv2 Management Communication Class A SNMPv2 management communication class corresponds to a | specific SNMPv2 PDU type defined in [2]. | A management communication class is represented by an ASN.1 INTEGER value according to the type of the identifying PDU (see Table 1). Get 1 - GetNext 2 Response 4 | Set 8 -- unused 16 | GetBulk 32 | Inform 64 | SNMPv2-Trap 128 | Table 1: Management Communication Classes The value by which a communication class is represented is computed as 2 raised to the value of the ASN.1 context- specific tag for the appropriate SNMPv2 PDU. | A set of management communication classes is represented by the ASN.1 INTEGER value that is the sum of the representations of the communication classes in that set. The null set is represented by the value zero. 2.11. SNMPv2 Access Control Policy A SNMPv2 access control policy is a specification of a local | access | policy in terms of the network management communication classes which are authorized between pairs of SNMPv2 parties. | Architecturally, such a specification comprises three parts: o the targets of SNMPv2 access control - the SNMPv2 parties | that may perform management operations as requested by management communications received from other parties, Expires June 6, 1993 [Page 12] Draft SNMPv2 Administrative Model Dec 92 o the subjects of SNMPv2 access control - the SNMPv2 | parties | that may request, by sending management communications to other parties, that management operations be performed, and o the policy that specifies the classes of SNMPv2 | management communications that a particular target is authorized to accept from a particular subject. Access to individual MIB object instances is determined implicitly since by definition each (target) SNMPv2 party | performs operations on | exactly one MIB view. Thus, defining the permitted access of a (reliably) identified subject party to a particular target party effectively defines the access permitted by that subject to that target's MIB view and, accordingly, to particular MIB object instances. Conceptually, a SNMPv2 access policy is represented by a | collection of | ASN.1 values with the following syntax: AclEntry ::= SEQUENCE { - aclTarget OBJECT IDENTIFIER, aclSubject OBJECT IDENTIFIER, aclPrivileges INTEGER } For each such value that represents one part of a SNMPv2 | access policy, | the following statements are true: o Its aclTarget component is called the target and | identifies the SNMPv2 party to which the partial policy | permits access. o Its aclSubject component is called the subject and | identifies the SNMPv2 party to which the partial policy | grants privileges. Expires June 6, 1993 [Page 13] Draft SNMPv2 Administrative Model Dec 92 o Its aclPrivileges component is called the privileges and | represents a set of SNMPv2 management communication | classes that are authorized to be processed by the specified target party when received from the specified subject party. Note that the application of SNMPv2 access control policy only + occurs on receipt of management communications; it is not + applied on transmission of management communications. + 2.12. SNMPv2 Proxy Party | A SNMPv2 proxy party is a SNMPv2 party that performs | management | operations by communicating with another, logically remote party. When communication between a logically remote party and a | SNMPv2 proxy party is via the SNMPv2 (over any transport | protocol), then the proxy party is called a SNMPv2 native | proxy party. Deployment of SNMPv2 native | proxy parties is a means whereby the processing or bandwidth costs of management may be amortized or shifted - thereby facilitating the construction of large management systems. When communication between a logically remote party and a | SNMPv2 proxy party is not via the SNMPv2, then the proxy party | is called a SNMPv2 | foreign proxy party. Deployment of foreign proxy parties is a means whereby otherwise unmanageable devices or portions of an internet may be managed via the SNMPv2. | The transparency principle that defines the behavior of a | SNMPv2 party in general applies in particular to a SNMPv2 | proxy party: | The manner in which one SNMPv2 party processes SNMPv2 | protocol messages received from another SNMPv2 party is | entirely transparent to the latter. | The transparency principle derives directly from the historical SNMP philosophy of divorcing architecture from implementation. To this dichotomy are attributable many of Expires June 6, 1993 [Page 14] Draft SNMPv2 Administrative Model Dec 92 the most valuable benefits in both the information and | distribution models of the Internet-standard Network | Management Framework, | and it is the architectural cornerstone upon which large management systems may be built. Consistent with this philosophy, although the implementation of SNMPv2 proxy agents | in certain environments may | resemble that of a transport-layer bridge, this particular implementation strategy (or any other!) does not merit special | recognition either in the SNMPv2 management architecture or in | standard | mechanisms for proxy administration. Implicit in the transparency principle is the requirement that the semantics of SNMPv2 management operations are preserved | between any two SNMPv2 peers. | In particular, the "as if simultaneous" semantics of a Set operation are extremely difficult to guarantee if its scope extends to management information resident at multiple network locations. For this reason, proxy configurations that admit Set operations that apply to information at multiple locations are discouraged, although such operations are not explicitly precluded by the architecture in those rare cases where they might be supported in a conformant way. Also implicit in the transparency principle is the requirement that, throughout its interaction with a proxy agent, a management station is supplied with no information about the nature or progress of the proxy mechanisms by which its requests are realized. That is, it should seem to the management station - except for any distinction in underlying | transport address - as if it were interacting via SNMPv2 | directly with the proxied device. Thus, a timeout in the communication between a proxy agent and its proxied device should be represented as a timeout in the communication between the management station and the proxy agent. Similarly, an error response from a proxied device should - as much as possible - be represented by the corresponding error response in the interaction between the proxy agent and management station. Expires June 6, 1993 [Page 15] Draft SNMPv2 Administrative Model Dec 92 2.13. Procedures This section describes the procedures followed by a SNMPv2 | entity in processing SNMPv2 messages. | These procedures are independent of the particular authentication and privacy protocols that may be in use. 2.13.1. Generating a Request This section describes the procedure followed by a SNMPv2 | entity whenever either a management request or a trap notification is to be transmitted by a SNMPv2 party. | (1) An ASN.1 SnmpMgmtCom value is constructed for which the srcParty component identifies the originating party, for which the dstParty component identifies the receiving party, and for which the other component represents the desired management operation. (2) The local database is consulted to determine the authentication protocol and other relevant information | for the originating and receiving SNMPv2 parties. | (3) An ASN.1 SnmpAuthMsg value is constructed with the following properties: Its authInfo component is constructed according to the authentication protocol specified for the originating party. In particular, if the authentication protocol for the originating SNMPv2 party is identified as | noAuth, | then this component corresponds to the OCTET STRING value of zero length. Its authData component is the constructed SnmpMgmtCom value. (4) The local database is consulted to determine the privacy protocol and other relevant information for the receiving | SNMPv2 party. | Expires June 6, 1993 [Page 16] Draft SNMPv2 Administrative Model Dec 92 (5) An ASN.1 SnmpPrivMsg value is constructed with the following properties: Its privDst component identifies the receiving | SNMPv2 party. | Its privData component is the (possibly encrypted) serialization of the SnmpAuthMsg value according to | the conventions of [5] and [2]. | In particular, if the privacy protocol for the | receiving SNMPv2 party is identified as noPriv, | then | the privData component is unencrypted. Otherwise, the privData component is processed according to the privacy protocol. (6) The constructed SnmpPrivMsg value is serialized according | to the conventions of [5] and [2]. | (7) The serialized SnmpPrivMsg value is transmitted using the transport address and transport domain for the receiving | SNMPv2 party. | Note that the above procedure above does not include any | application of any SNMPv2 access control policy (see section | 2.11). | 2.13.2. Processing a Received Communication This section describes the procedure followed by a SNMPv2 | entity whenever a management communication is received. (1) If the received message is not the serialization (according to the conventions of [5] and [2]) of an ASN.1 | SnmpPrivMsg value, then that message is discarded without further processing. (2) The local database is consulted for information about the | receiving SNMPv2 party identified by the privDst | component of the SnmpPrivMsg value. (3) If information about the receiving SNMPv2 party is absent | from the local database, or specifies a transport domain Expires June 6, 1993 [Page 17] Draft SNMPv2 Administrative Model Dec 92 and address which indicates that the receiving party's | operation is not realized by the local SNMPv2 | entity, then the received message is discarded without further processing. (4) An ASN.1 OCTET STRING value is constructed (possibly by decryption, according to the privacy protocol in use) from the privData component of said SnmpPrivMsg value. In particular, if the privacy protocol recorded for the party is noPriv, then the OCTET STRING value corresponds exactly to the privData component of the SnmpPrivMsg value. (5) If the OCTET STRING value is not the serialization | (according to the conventions of [5] and [2]) of an ASN.1 | SnmpAuthMsg value, then the received message is discarded without further processing. (6) If the dstParty component of the authData component of the obtained SnmpAuthMsg value is not the same as the privDst component of the SnmpPrivMsg value, then the received message is discarded without further processing. (7) The local database is consulted for information about the | originating SNMPv2 party identified by the srcParty | component of the authData component of the SnmpAuthMsg value. (8) If information about the originating SNMPv2 party is | absent from the local database, then the received message is discarded without further processing. (9) The obtained SnmpAuthMsg value is evaluated according to the authentication protocol and other relevant | information associated with the originating and receiving | SNMPv2 parties in the local database. | In particular, if the authentication protocol is identified as noAuth, then the SnmpAuthMsg value is always evaluated as authentic. (10) If the SnmpAuthMsg value is evaluated as unauthentic, then the received message is discarded without further processing, and an authentication failure is noted. Expires June 6, 1993 [Page 18] Draft SNMPv2 Administrative Model Dec 92 (11) The ASN.1 SnmpMgmtCom value is extracted from the authData component of the SnmpAuthMsg value. (12) The local database is consulted for access privileges permitted by the local access policy to the originating | SNMPv2 party with respect to the receiving SNMPv2 party. | (13) The management communication class is determined from the ASN.1 tag value associated with the PDUs component of the | SnmpMgmtCom value. | (14) If the management communication class of the received | message is either 128 or 4 (i.e., SNMPv2-Trap or | Response) and | this class is not among the access privileges, then the received message is discarded without further processing. (15) If the management communication class of the received message is not among the access privileges, then the received message is discarded without further processing after generation and transmission of a response message. This response message is directed to the originating | SNMPv2 party on behalf of the receiving SNMPv2 party. | Its var-bind-list and request-id components are identical to those of the received request. Its error-index component is zero and its error-status component is | authorizationError [2]. | (16) If the proxied party associated with the receiving SNMPv2 | party in the local database is identified as noProxy, then the management operation represented by the SnmpMgmtCom value is performed by the receiving SNMPv2 | entity with respect to the MIB view identified with the | receiving SNMPv2 party according to the procedures set | forth in [2]. | (17) If the proxied party associated with the receiving SNMPv2 | party in the local database is not identified as noProxy, then the management operation represented by the SnmpMgmtCom value is performed through appropriate | cooperation between the receiving SNMPv2 | party and the identified proxied party. In particular, if the transport domain associated with the identified proxied party in the local database is | Expires June 6, 1993 [Page 19] Draft SNMPv2 Administrative Model Dec 92 snmpUDPDomain, then the operation requested by | the received message is performed by the generation of a corresponding request to the proxied party on behalf of the receiving party. If the received message requires a | response from the local SNMPv2 entity, then that | response is subsequently generated from the response (if any) received from the proxied party corresponding to the newly generated request. 2.13.3. Generating a Response The procedure for generating a response to a SNMPv2 management | request | is identical to the procedure for transmitting a request (see Section 2.13.1), except for the derivation of the transport | domain and | address information. This exception is that a response is | transmitted using the transport domain and address from which | its corresponding request | originated - even if that is different from the transport information recorded in the local database. 3. Application of the Model This section describes how the administrative model set forth above is applied to realize effective network management in a variety of configurations and environments. Several types of administrative configurations are identified, and an example of each is presented. 3.1. Non-Secure Minimal Agent Configuration This section presents an example configuration for a minimal, | non-secure SNMPv2 agent that interacts with one or more SNMPv2 | management | stations. Table 2 presents information about SNMPv2 parties | that is | known both to the minimal agent and to the manager, while Table 3 presents similarly common information about the local access policy. Expires June 6, 1993 [Page 20] Draft SNMPv2 Administrative Model Dec 92 As represented in Table 2, the example agent party operates at UDP port 161 at IP address 1.2.3.4 using the party identity gracie; the example manager operates at UDP port 2001 at IP address 1.2.3.5 using the identity george. At minimum, a | non-secure SNMPv2 agent | implementation must provide for administrative configuration (and non-volatile storage) of the identities and transport addresses of two SNMPv2 parties: itself and a remote peer. | Strictly speaking, other information about these two parties (including access policy information) need not be configurable. Identity gracie george (agent) (manager) Domain snmpUDPDomain snmpUDPDomain | Address 1.2.3.4, 161 1.2.3.5, 2001 Proxied Party noProxy noProxy Auth Prot noAuth noAuth Auth Priv Key "" "" Auth Pub Key "" "" Auth Clock 0 0 Auth Lifetime 0 0 - Priv Prot noPriv noPriv Priv Priv Key "" "" Priv Pub Key "" "" Table 2: Party Information for Minimal Agent Target Subject Privileges gracie george 35 (Get, GetNext & GetBulk) | george gracie 132 (Response & SNMPv2-Trap) | Table 3: Access Information for Minimal Agent Suppose that the managing party george wishes to interrogate the agent named gracie by issuing a SNMPv2 GetNext request | message. | Expires June 6, 1993 [Page 21] Draft SNMPv2 Administrative Model Dec 92 The manager consults its local database of party information. Because the authentication protocol for the party george is recorded as noAuth, the GetNext request message generated by the manager is not authenticated as to origin and integrity. Because, according to the manager's database, the privacy protocol for the party gracie is noPriv, the GetNext request message is not protected from disclosure. Rather, it is simply assembled, serialized, and transmitted to the transport address (IP address 1.2.3.4, UDP port 161) associated in the manager's database with the party gracie. When the GetNext request message is received at the agent, the identity of the party to which it is directed (gracie) is extracted from the message, and the receiving entity consults | its | local database of party information. Because the privacy protocol for the party gracie is recorded as noPriv, the received message is assumed not to be protected from disclosure. Similarly, the identity of the originating party (george) is extracted, and the local party database is consulted. Because the authentication protocol for the party george is recorded as noAuth, the received message is immediately accepted as authentic. The received message is fully processed only if the access policy database local to the agent authorizes GetNext request communications by the party george with respect to the agent party gracie. The access policy database presented as Table 3 authorizes such communications (as well as Get and GetBulk | operations). | When the received request is processed, a Response message is | generated with gracie as the source party and george, the party from which the request originated, as the destination party. Because the authentication protocol for gracie is recorded in the local party database as noAuth, the generated | Response message is not | authenticated as to origin or integrity. Because, according to the local database, the privacy protocol for the party george is noPriv, the response message is not protected from disclosure. The response message is transmitted to the transport address from which the corresponding request originated - without regard for the transport address associated with george in the local database. Expires June 6, 1993 [Page 22] Draft SNMPv2 Administrative Model Dec 92 When the generated response is received by the manager, the identity of the party to which it is directed (george) is extracted from the message, and the manager consults its local database of party information. Because the privacy protocol for the party george is recorded as noPriv, the received response is assumed not to be protected from disclosure. Similarly, the identity of the originating party (gracie) is extracted, and the local party database is consulted. Because the authentication protocol for the party gracie is recorded as noAuth, the received response is immediately accepted as authentic. The received message is fully processed only if the access policy database local to the manager authorizes Response | communications | by the party gracie with respect to the manager party george. The access policy database presented as Table 3 authorizes | such Response messages (as well as SNMPv2-Trap messages). | 3.2. Secure Minimal Agent Configuration This section presents an example configuration for a secure, minimal SNMPv2 agent that interacts with a single SNMPv2 | management station. Table 4 presents information about SNMPv2 | parties that is known both to | the minimal agent and to the manager, while Table 5 presents similarly common information about the local access policy. The interaction of manager and agent in this configuration is very similar to that sketched above for the non-secure minimal agent - except that all protocol messages are authenticated as to origin and integrity and protected from disclosure. This example requires encryption in order to support distribution of secret keys via the SNMPv2 itself. | A more elaborate example comprising an additional pair of | SNMPv2 parties could support the exchange of non-secret | information | in authenticated messages without incurring the cost of encryption. An actual secure agent configuration may require SNMPv2 | parties for | which the authentication and privacy protocols are noAuth and noPriv, respectively, in order to support clock | Expires June 6, 1993 [Page 23] Draft SNMPv2 Administrative Model Dec 92 synchronization (see [6]). | For clarity, these additional parties are not represented in this example. Identity ollie stan (agent) (manager) Domain snmpUDPDomain snmpUDPDomain | Address 1.2.3.4, 161 1.2.3.5, 2001 Proxied Party noProxy noProxy Auth Prot v2md5AuthProtocol v2md5AuthProtocol | Auth Priv Key "0123456789ABCDEF" "GHIJKL0123456789" Auth Pub Key "" "" Auth Clock 0 0 Auth Lifetime 500 500 - Priv Prot desPrivProtocol desPrivProtocol Priv Priv Key "MNOPQR0123456789" "STUVWX0123456789" Priv Pub Key "" "" Table 4: Party Information for Secure Minimal Agent Target Subject Privileges ollie stan 35 (Get, GetNext & GetBulk) | stan ollie 132 (Response & SNMPv2-Trap) | Table 5: Access Information for Secure Minimal Agent As represented in Table 4, the example agent party operates at UDP port 161 at IP address 1.2.3.4 using the party identity ollie; the example manager operates at UDP port 2001 at IP address 1.2.3.5 using the identity stan. At minimum, a secure | SNMPv2 agent implementation | must provide for administrative configuration (and non- volatile storage) of relevant information about two SNMPv2 | parties: itself and a | remote peer. Both ollie and stan authenticate all messages that they generate by using the SNMPv2 authentication protocol | v2md5AuthProtocol | and their distinct, private authentication keys. Although Expires June 6, 1993 [Page 24] Draft SNMPv2 Administrative Model Dec 92 these private authentication key values ("0123456789ABCDEF" and "GHIJKL0123456789") are presented here for expository purposes, knowledge of private authentication keys is not normally afforded to human beings and is confined to those portions of the protocol implementation that require it. When using the v2md5AuthProtocol, the public authentication | key for each SNMPv2 party is never used in authentication and | verification of SNMPv2 exchanges. Also, because the | v2md5AuthProtocol is symmetric in | character, the private authentication key for each party must be known to another SNMPv2 party with which authenticated | communication is | desired. In contrast, asymmetric (public key) authentication protocols would not depend upon sharing of a private key for their operation. All protocol messages generated for transmission to the party | stan are encrypted using the desPrivProtocol privacy protocol | and the | private key "STUVWX0123456789"; they are decrypted upon reception according to the same protocol and key. Similarly, all messages generated for transmission to the party ollie are | encrypted using the | desPrivProtocol protocol and private privacy key "MNOPQR0123456789"; they are correspondingly decrypted on reception. As with authentication keys, knowledge of private privacy keys is not normally afforded to human beings and is confined to those portions of the protocol implementation that require it. 3.3. Proxy Configuration This section presents examples of SNMPv2 proxy configurations. | On one hand, foreign proxy configurations provide the capability to manage non-SNMP devices. On the other hand, native proxy configurations allow an administrator to shift the computational burden of rich management functionality away from network devices whose primary task is not management. To | the extent that SNMPv2 proxy agents function as | points of aggregation for management information, proxy | configurations may also reduce the bandwidth requirements of | large-scale management activities. | Expires June 6, 1993 [Page 25] Draft SNMPv2 Administrative Model Dec 92 The example configurations in this section are simplified for clarity: actual configurations may require additional parties in order to support clock synchronization and distribution of secrets. 3.3.1. Foreign Proxy Configuration This section presents an example configuration by which a | SNMPv2 | management station may manage network elements that do not themselves support the SNMPv2. This configuration centers on | a SNMPv2 proxy agent that realizes SNMPv2 management | operations by interacting with a non-SNMPv2 device using a | proprietary protocol. | Table 6 presents information about SNMPv2 parties that is | recorded in the local database of the SNMPv2 proxy agent. | Table 7 presents information about SNMPv2 parties that is | recorded in the local database of the SNMPv2 management | station. | Table 8 presents information about the access policy specified by the local administration. Identity larry moe curly (manager) (proxy) (proxied) Domain snmpUDPDomain snmpUDPDomain acmeMgmtPrtcl| Address 1.2.3.4, 2002 1.2.3.5, 161 0x98765432 Proxied Party noProxy curly noProxy Auth Prot v2md5AuthProtocol v2md5AuthProtocol noAuth | Auth Priv Key "0123456789ABCDEF" "GHIJKL0123456789" "" Auth Pub Key "" "" "" Auth Clock 0 0 0 Auth Lifetime 500 500 0 - Priv Prot noPriv noPriv noPriv Priv Priv Key "" "" "" Priv Pub Key "" "" "" Table 6: Party Information for Proxy Agent Expires June 6, 1993 [Page 26] Draft SNMPv2 Administrative Model Dec 92 Identity larry moe (manager) (proxy) Domain snmpUDPDomain snmpUDPDomain | Address 1.2.3.4, 2002 1.2.3.5, 161 Proxied Party noProxy noProxy Auth Prot v2md5AuthProtocol v2md5AuthProtocol | Auth Priv Key "0123456789ABCDEF" "GHIJKL0123456789" Auth Pub Key "" "" Auth Clock 0 0 Auth Lifetime 500 500 - Priv Prot noPriv noPriv Priv Priv Key "" "" Priv Pub Key "" "" Table 7: Party Information for Management Station Target Subject Privileges moe larry 35 (Get, GetNext & GetBulk) | larry moe 132 (Response & SNMPv2-Trap) | Table 8: Access Information for Foreign Proxy As represented in Table 6, the proxy agent party operates at UDP port 161 at IP address 1.2.3.5 using the party identity moe; the example manager operates at UDP port 2002 at IP address 1.2.3.4 using the identity larry. Both larry and moe authenticate all messages that they generate by using the | protocol v2md5AuthProtocol and their | distinct, private authentication keys. Although these private authentication key values ("0123456789ABCDEF" and "GHIJKL0123456789") are presented here for expository purposes, knowledge of private keys is not normally afforded to human beings and is confined to those portions of the protocol implementation that require it. Although all SNMPv2 agents that use cryptographic keys in | their | communication with other protocol entities will almost certainly engage in private SNMPv2 exchanges to distribute | Expires June 6, 1993 [Page 27] Draft SNMPv2 Administrative Model Dec 92 those keys, in order | to simplify this example, neither the management station nor the proxy agent sends or receives private SNMPv2 | communications. | Thus, the privacy protocol for each of them is recorded as noPriv. The party curly does not send or receive SNMPv2 protocol | messages; | rather, all communication with that party proceeds via a hypothetical proprietary protocol identified by the value acmeMgmtPrtcl. Because the party curly does not participate | in the SNMPv2, many of the | attributes recorded for that party in a local database are ignored. In order to interrogate the proprietary device associated with the party curly, the management station larry constructs a | SNMPv2 GetNext | request and transmits it to the party moe operating (see Table 7) at UDP port 161, and IP address 1.2.3.5. This request is authenticated using the private authentication key "0123456789ABCDEF." When that request is received by the party moe, the originator of the message is verified as being the party larry by using local knowledge (see Table 6) of the private authentication key "0123456789ABCDEF." Because party larry is authorized to issue GetNext requests with respect to party moe by the relevant access control policy (Table 8), the request is accepted. Because the local database records the proxied party for party moe as curly, the request is satisfied by its translation into appropriate operations of the acmeMgmtPrtcl directed at party curly. These new operations are transmitted to the party curly at the address 0x98765432 in the acmeMgmtPrtcl domain. When and if the proprietary protocol exchange between the proxy agent and the proprietary device concludes, a SNMPv2 | Response management operation is constructed by the SNMPv2 | party moe to relay the results | to party larry. This response communication is authenticated as to origin and integrity using the authentication protocol | v2md5AuthProtocol and private authentication key | "GHIJKL0123456789" | Expires June 6, 1993 [Page 28] Draft SNMPv2 Administrative Model Dec 92 specified for transmissions from party moe. It is then transmitted to the SNMPv2 party larry operating at the | management station at IP | address 1.2.3.4 and UDP port 2002 (the source address for the corresponding request). When this response is received by the party larry, the originator of the message is verified as being the party moe by using local knowledge (see Table 7) of the private authentication key "GHIJKL0123456789." Because party moe is authorized to issue Response communications with respect to | party larry by the | relevant access control policy (Table 8), the response is accepted, and the interrogation of the proprietary device is complete. It is especially useful to observe that the database of SNMPv2 | parties | recorded at the proxy agent (Table 6) need be neither static nor configured exclusively by the management station. For instance, suppose that, in this example, the acmeMgmtPrtcl was a proprietary, MAC-layer mechanism for managing stations attached to a local area network. In such an environment, the | SNMPv2 party moe would reside at a SNMPv2 proxy agent attached | to such a LAN and could, by participating | in the LAN protocols, detect the attachment and disconnection of various stations on the LAN. In this scenario, the SNMPv2 | proxy agent could easily adjust its local database of SNMPv2 | parties to support indirect management of the LAN stations by | the SNMPv2 management | station. For each new LAN station detected, the SNMPv2 proxy | agent | would add to its database both an entry analogous to that for party curly (representing the new LAN station itself) and an entry analogous to that for party moe (representing a proxy for that new station in the SNMPv2 domain). | By using the SNMPv2 to interrogate the database of parties | held locally by the SNMPv2 proxy agent, a SNMPv2 management | station can discover and | interact with new stations as they are attached to the LAN. Expires June 6, 1993 [Page 29] Draft SNMPv2 Administrative Model Dec 92 3.3.2. Native Proxy Configuration This section presents an example configuration that supports | SNMPv2 native proxy operations - indirect interaction between | a SNMPv2 agent and a management station that is mediated by a | second SNMPv2 (proxy) | agent. This example configuration is similar to that presented in the | discussion of SNMPv2 foreign proxy above. | In this example, however, the party associated with the identity curly receives messages via the SNMPv2, and, | accordingly interacts with the SNMPv2 proxy agent moe using | authenticated SNMPv2 communications. | Table 9 presents information about SNMPv2 parties that is | recorded in the local database of the SNMPv2 proxy agent. | Table 7 presents information about SNMPv2 parties that is | recorded in the local database of the SNMPv2 management | station. | Table 10 presents information about the access policy specified by the local administration. Identity larry moe curly (manager) (proxy) (proxied) Domain snmpUDPDomain snmpUDPDomain snmpUDPDomain| Address 1.2.3.4, 2002 1.2.3.5, 161 1.2.3.6, 16 Proxied Party noProxy curly noProxy Auth Prot v2md5AuthProtocol v2md5AuthProtocol v2md5AuthProtocol| Auth Priv Key "0123456789ABCDEF" "GHIJKL0123456789" "MNOPQR0123456789" Auth Pub Key "" "" "" Auth Clock 0 0 0 Auth Lifetime 500 500 500 - Priv Prot noPriv noPriv noPriv Priv Priv Key "" "" "" Priv Pub Key "" "" "" Table 9: Party Information for Proxy Agent Expires June 6, 1993 [Page 30] Draft SNMPv2 Administrative Model Dec 92 Target Subject Privileges moe larry 35 (Get, GetNext & GetBulk) | larry moe 132 (Response & SNMPv2-Trap) | curly moe 35 (Get, GetNext & GetBulk) | moe curly 132 (Response & SNMPv2-Trap) | Table 10: Access Information for Native Proxy As represented in Table 9, the proxy party operates at UDP port 161 at IP address 1.2.3.5 using the party identity moe; the example manager operates at UDP port 2002 at IP address 1.2.3.4 using the identity larry; the proxied party operates at UDP port 161 at IP address 1.2.3.6 using the party identity curly. Messages generated by all three SNMPv2 parties are | authenticated as to origin and integrity by using the | authentication protocol v2md5AuthProtocol | and distinct, private authentication keys. Although these private key values ("0123456789ABCDEF," "GHIJKL0123456789," and "MNOPQR0123456789") are presented here for expository purposes, knowledge of private keys is not normally afforded to human beings and is confined to those portions of the protocol implementation that require it. In order to interrogate the proxied device associated with the party curly, the management station larry constructs a SNMPv2 | GetNext request | and transmits it to the party moe operating (see Table 7) at UDP port 161 and IP address 1.2.3.5. This request is authenticated using the private authentication key "0123456789ABCDEF." When that request is received by the party moe, the originator of the message is verified as being the party larry by using local knowledge (see Table 9) of the private authentication key "0123456789ABCDEF." Because party larry is authorized to | issue GetNext (as well as Get and GetBulk) requests | with respect to party moe by the relevant access control policy (Table 10), the request is accepted. Because the local database records the proxied party for party moe as curly, the request is satisfied by its translation into a corresponding | SNMPv2 GetNext | request directed from party moe to party curly. This new communication is authenticated using the private Expires June 6, 1993 [Page 31] Draft SNMPv2 Administrative Model Dec 92 authentication key "GHIJKL0123456789" and transmitted to party curly at the IP address 1.2.3.6. When this new request is received by the party curly, the originator of the message is verified as being the party moe by using local knowledge (see Table 9) of the private authentication key "GHIJKL0123456789." Because party moe is authorized to issue GetNext (as well as Get and GetBulk) | requests with respect to party curly by the relevant access | control policy (Table 10), the request is accepted. Because the local database records the proxied party for party curly as noProxy, the GetNext request is satisfied by local mechanisms. A SNMPv2 Response | message representing the results of the query is then generated by party curly. This response communication is authenticated as to origin and integrity using the private authentication key "MNOPQR0123456789" and transmitted to party moe at IP address 1.2.3.5 (the source address for the corresponding request). When this response is received by party moe, the originator of the message is verified as being the party curly by using local knowledge (see Table 9) of the private authentication key "MNOPQR0123456789." Because party curly is authorized to | issue Response communications | with respect to party moe by the relevant access control policy (Table 10), the response is not rejected. Instead, it is translated into a response to the original GetNext request from party larry. This response is authenticated as to origin and integrity using the private authentication key "GHIJKL0123456789" and is transmitted to the party larry at IP address 1.2.3.4 (the source address for the original request). When this response is received by the party larry, the originator of the message is verified as being the party moe by using local knowledge (see Table 7) of the private authentication key "GHIJKL0123456789." Because party moe is authorized to issue Response communications with respect to | party larry by the | relevant access control policy (Table 10), the response is accepted, and the interrogation is complete. Expires June 6, 1993 [Page 32] Draft SNMPv2 Administrative Model Dec 92 3.4. Public Key Configuration This section presents an example configuration predicated upon a hypothetical security protocol. This hypothetical protocol would be based on asymmetric (public key) cryptography as a means for providing data origin authentication (but not protection against disclosure). This example illustrates the consistency of the administrative model with public key technology, and the extension of the example to support protection against disclosure should be apparent. Identity ollie stan (agent) (manager) Domain snmpUDPDomain snmpUDPDomain | Address 1.2.3.4, 161 1.2.3.5, 2004 Proxied Party noProxy noProxy Auth Prot pkAuthProtocol pkAuthProtocol Auth Priv Key "0123456789ABCDEF" "" Auth Pub Key "" "ghijkl0123456789" Auth Clock 0 0 Auth Lifetime 500 500 - Priv Prot noPriv noPriv Priv Priv Key "" "" Priv Pub Key "" "" Table 11: Party Information for Public Key Agent The example configuration comprises a single SNMPv2 agent that | interacts with a single SNMPv2 management station. | Tables 11 and 12 present information about SNMPv2 parties that | is by the agent and | manager, respectively, while Table 5 presents information about the local access policy that is known to both manager and agent. Expires June 6, 1993 [Page 33] Draft SNMPv2 Administrative Model Dec 92 Identity ollie stan (agent) (manager) Domain snmpUDPDomain snmpUDPDomain | Address 1.2.3.4, 161 1.2.3.5, 2004 Proxied Party noProxy noProxy Auth Prot pkAuthProtocol pkAuthProtocol Auth Priv Key "" "GHIJKL0123456789" Auth Pub Key "0123456789abcdef" "" Auth Clock 0 0 Auth Lifetime 500 500 - Priv Prot noPriv noPriv Priv Priv Key "" "" Priv Pub Key "" "" Table 12: Party Information for Public Key Management Station As represented in Table 11, the example agent party operates at UDP port 161 at IP address 1.2.3.4 using the party identity ollie; the example manager operates at UDP port 2004 at IP address 1.2.3.5 using the identity stan. Both ollie and stan authenticate all messages that they generate as to origin and integrity by using the hypothetical SNMPv2 authentication | protocol pkAuthProtocol and their distinct, | private authentication keys. Although these private authentication key values ("0123456789ABCDEF" and "GHIJKL0123456789") are presented here for expository purposes, knowledge of private keys is not normally afforded to human beings and is confined to those portions of the protocol implementation that require it. In most respects, the interaction between manager and agent in this configuration is almost identical to that in the example of the minimal, secure SNMPv2 agent described above. | The most significant difference is that neither SNMPv2 party | in the public key configuration | has knowledge of the private key by which the other party authenticates its transmissions. Instead, for each received | authenticated SNMPv2 communication, the identity of the | originator is | verified by applying an asymmetric cryptographic algorithm to the received message together with the public authentication key for the originating party. Thus, in this configuration, the agent knows the manager's public key ("ghijkl0123456789") Expires June 6, 1993 [Page 34] Draft SNMPv2 Administrative Model Dec 92 but not its private key ("GHIJKL0123456789"); similarly, the manager knows the agent's public key ("0123456789abcdef") but not its private key ("0123456789ABCDEF"). For simplicity, privacy protocols are not addressed in this example configuration, although their use would be necessary to the secure, automated distribution of secret keys. 3.5. MIB View Configurations This section describes a convention for the definition of MIB views and, using that convention, presents example configurations of MIB views for SNMPv2 parties. | A MIB view is defined by a collection of view subtrees (see Section 2.6), and any MIB view may be represented in this way. | Because MIB view definitions may, in certain cases, comprise a very large number of view subtrees, a convention for abbreviating MIB view definitions is desirable. The convention adopted in [4] supports abbreviation of MIB | view | definitions in terms of families of view subtrees that are either included in or excluded from the definition of the relevant MIB view. By this convention, a table locally | maintained by each SNMPv2 entity defines the MIB view | associated with each SNMPv2 party realized by that | entity. Each entry in the table represents a family of view subtrees that (according to the type of that entry) is either | included in or excluded from the MIB view of some SNMPv2 | party. | Each table entry represents a subtree family as a pairing of an OBJECT IDENTIFIER value (called the family name) together with a bitstring value (called the family mask). The family mask indicates which subidentifiers of the associated family name are significant to the definition of the represented subtree family. For each possible MIB object instance, that instance belongs to the view subtree family represented by a particular table entry if o the OBJECT IDENTIFIER name of that MIB object instance comprises at least as many subidentifiers as does the family name for said table entry, and Expires June 6, 1993 [Page 35] Draft SNMPv2 Administrative Model Dec 92 o each subidentifier in the name of said MIB object instance matches the corresponding subidentifier of the relevant family name whenever the corresponding bit of the associated family mask is non-zero. The appearance of a MIB object instance in the MIB view for a particular | SNMPv2 party is related to the membership of that | instance | in the subtree families associated with that party in local table entries: o If a MIB object instance belongs to none of the relevant subtree families, then that instance is not in the MIB | view for the relevant SNMPv2 party. | o If a MIB object instance belongs to the subtree family represented by exactly one of the relevant table entries, then that instance is included in, or excluded from, the | relevant MIB view according to the type of that entry. | o If a MIB object instance belongs to the subtree families represented by more than one of the relevant table entries, then that instance is included in, or excluded | from, the relevant MIB view according to the type of | the single such table entry for which, first, the associated family name comprises the greatest number of subidentifiers, and, second, the associated family name is lexicographically greatest. The subtree family represented by a table entry for which the associated family mask is all ones corresponds to the single view subtree identified by the family name for that entry. Because the convention of [4] provides for implicit extension | of family mask | values with ones, the subtree family represented by a table entry with a family mask of zero length always corresponds to a single view subtree. Party Identity Type Family Name Family Mask | lucy included internet ''H | Table 13: View Definition for Minimal Agent Expires June 6, 1993 [Page 36] Draft SNMPv2 Administrative Model Dec 92 Using this convention for abbreviating MIB view definitions, some of the most common definitions of MIB views may be conveniently expressed. For example, Table 13 illustrates the MIB view definitions required for a minimal SNMPv2 entity that | locally realizes a single SNMPv2 party for which the | associated MIB view embraces all instances of all MIB objects | defined within the SNMPv2 Network Management Framework. | The represented table has a single entry. The SNMPv2 party | (lucy) for which that entry defines the MIB view is identified in the first column. The type of that entry (included) | signifies that any | MIB object instance belonging to the subtree family represented by that entry may appear in the MIB view for party lucy. The family name for that entry is internet, and the zero-length family mask value signifies that the relevant subtree family corresponds to the single view subtree rooted at that node. Another example of MIB view definition (see Table 14) is that of a SNMPv2 entity that locally realizes multiple SNMPv2 | parties with | distinct MIB views. The MIB view associated with the party lucy comprises all instances of all MIB objects defined within the SNMPv2 Network Management Framework, except those | pertaining to the administration of SNMPv2 parties. | In contrast, the MIB view attributed to the party ricky contains only MIB object instances defined in the system group of the internet-standard MIB together with those object | instances by which SNMPv2 parties are administered. | Party Identity Type Family Name Family Mask | lucy included internet ''H | lucy excluded snmpParties ''H | ricky included system ''H | ricky included snmpParties ''H | Table 14: View Definition for Multiple Parties A more complicated example of MIB view configuration illustrates the abbreviation of related collections of view subtrees by view subtree families (see Table 15). In this example, the MIB view associated with party lucy includes all Expires June 6, 1993 [Page 37] Draft SNMPv2 Administrative Model Dec 92 object instances in the system group of the internet-standard MIB together with some information related to the second network interface attached to the managed device. However, this interface-related information does not include the speed of the interface. The family mask value 'FFA0'H in the second | table entry signifies that a MIB | object instance belongs to the relevant subtree family if the initial prefix of its name places it within the ifEntry portion of the registration hierarchy and if the eleventh subidentifier of its name is 2. The MIB object instance representing the speed of the second network interface belongs to the subtree families represented by both the second and third entries of the table, but that particular instance is excluded from the MIB view for party lucy because the lexicographically greater of the relevant family names appears in the table entry with type excluded. | The MIB view for party ricky is also defined in this example. The MIB view attributed to the party ricky includes all object instances in the icmp group of the internet-standard MIB, together with all information relevant to the fifth network interface attached to the managed device. In addition, the MIB view attributed to party ricky includes the number of octets received on the fourth attached network interface. Party Identity Type Family Name Family Mask | lucy included system ''H | lucy included { ifEntry 0 2 } 'FFA0'H | lucy excluded { ifSpeed 2 } ''H | ricky included icmp ''H | ricky included { ifEntry 0 5 } 'FFA0'H | ricky included { ifInOctets 4 } ''H | Table 15: More Elaborate View Definitions While, as suggested by the examples above, a wide range of MIB view configurations are efficiently supported by the abbreviated representation of [4], prudent MIB design can | sometimes further | reduce the size and complexity of the most likely MIB view definitions. On one hand, it is critical that mechanisms for MIB view configuration impose no absolute constraints either Expires June 6, 1993 [Page 38] Draft SNMPv2 Administrative Model Dec 92 upon the access policies of local administrations or upon the structure of MIB namespaces; on the other hand, where the most common access policies are known, the configuration costs of realizing those policies may be slightly reduced by assigning to distinct portions of the registration hierarchy those MIB objects for which local policies most frequently require distinct treatment. The relegation in [4] of | certain objects to a distinct arc in the MIB namespace is an example of this kind of optimization. 4. Compatibility Ideally, all management stations and agents would communicate | exclusively using the secure facilities described in this memo. In reality, many SNMP agents may implement only the | insecure SNMPv1 | mechanisms described in [1] for some time to come. New agent implementations should never implement both the | insecure mechanisms of [1] and the facilities described here. Rather, consistent with the SNMP philosophy, the burden of supporting both sorts of communication should fall entirely upon managers. Perhaps the best way to realize both old and new modes of communication is by the use of a SNMPv2 proxy | agent deployed locally on the same system | with a management station implementation. The management station implementation itself operates exclusively by using the newer, secure modes of communication, and the local proxy agent translates the requests of the manager into older, insecure modes as needed. - 5. Security Considerations It is important to note that, in the example configuration for native proxy operations presented in this memo, the use of symmetric cryptography does not securely prevent direct communication between the SNMPv2 management station and the | proxied SNMPv2 agent. | While secure isolation of the management station and the proxied agent can, according to the administrative model set forth in this memo, be realized using symmetric cryptography, the required configuration is more complex and is not Expires June 6, 1993 [Page 39] Draft SNMPv2 Administrative Model Dec 92 described in this memo. Rather, it is recommended that native proxy configurations that require secure isolation of management station from proxied agent be implemented using security protocols based on asymmetric (or "public key") cryptography. However, no SNMPv2 security protocols based on | asymmetric cryptography are currently defined. In order to participate in the administrative model set forth in this memo, SNMPv2 implementations must support local, non- | volatile storage | of the local party database. Accordingly, every attempt has been made to minimize the amount of non-volatile storage required. Expires June 6, 1993 [Page 40] Draft SNMPv2 Administrative Model Dec 92 6. Acknowledgements This document is based, almost entirely, on RFC 1351. + Expires June 6, 1993 [Page 41] Draft SNMPv2 Administrative Model Dec 92 7. References [1] J.D. Case, M.S. Fedor, M.L. Schoffstall, and J.R. Davin, | Simple Network Management Protocol. Request for Comments | 1157, (May, 1990). | [2] J.D. Case, K. McCloghrie, M.T. Rose, S.L. Waldbusser, | Protocol Operations for version 2 of the Simple Network | Management Protocol (SNMPv2). Internet-Draft, (December | 4, 1992). | [3] J.D. Case, K. McCloghrie, M.T. Rose, S.L. Waldbusser, | Structure of Management Information for version 2 of the | Simple Network Management Protocol (SNMPv2). Internet- | Draft, (December 4, 1992). | [4] K. McCloghrie, J.R. Davin, J.M. Galvin, Party MIB for | version 2 of the Simple Network Management Protocol | (SNMPv2). Internet-Draft, (December 6, 1992). | [5] J.D. Case, K. McCloghrie, M.T. Rose, S.L. Waldbusser, | Transport Mappings for version 2 of the Simple Network | Management Protocol (SNMPv2). Internet-Draft, (December | 4, 1992). | [6] J.M. Galvin, K. McCloghrie, J.R. Davin, Security | Protocols for version 2 of the Simple Network Management | Protocol (SNMPv2). Internet-Draft, (December 6, 1992). | Expires June 6, 1993 [Page 42] Draft SNMPv2 Administrative Model Dec 92 Table of Contents 1 Introduction .......................................... 2 1.1 A Note on Terminology ............................... 2 2 Elements of the Model ................................. 3 2.1 SNMPv2 Party ........................................ 3 2.2 SNMPv2 Entity ....................................... 6 2.3 SNMPv2 Management Station ........................... 7 2.4 SNMPv2 Agent ........................................ 7 2.5 View Subtree ........................................ 8 2.6 MIB View ............................................ 8 2.7 SNMPv2 Management Communication ..................... 9 2.8 SNMPv2 Authenticated Management Communication ....... 10 2.9 SNMPv2 Private Management Communication ............. 11 2.10 SNMPv2 Management Communication Class .............. 12 2.11 SNMPv2 Access Control Policy ....................... 12 2.12 SNMPv2 Proxy Party ................................. 14 2.13 Procedures ......................................... 16 2.13.1 Generating a Request ............................. 16 2.13.2 Processing a Received Communication .............. 17 2.13.3 Generating a Response ............................ 20 3 Application of the Model .............................. 20 3.1 Non-Secure Minimal Agent Configuration .............. 20 3.2 Secure Minimal Agent Configuration .................. 23 3.3 Proxy Configuration ................................. 25 3.3.1 Foreign Proxy Configuration ....................... 26 3.3.2 Native Proxy Configuration ........................ 30 3.4 Public Key Configuration ............................ 33 3.5 MIB View Configurations ............................. 35 4 Compatibility ......................................... 39 5 Security Considerations ............................... 39 6 Acknowledgements ...................................... 41 7 References ............................................ 42 Expires June 6, 1993 [Page 43]