RFCs in HTML Format


RFC 1592

                   Simple Network Management Protocol
                     Distributed Protocol Interface
                              Version 2.0

Table of Contents
     1. INTRODUCTION  . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1  Motivation  . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2  Summary of Changes  . . . . . . . . . . . . . . . . . . . .  4
     2. THEORY OF OPERATION . . . . . . . . . . . . . . . . . . . . .  5
     2.1  Connection Establishment and Termination  . . . . . . . . .  5
     2.2  Registration  . . . . . . . . . . . . . . . . . . . . . . .  6
     2.3  Normal Operation  . . . . . . . . . . . . . . . . . . . . .  6
     2.4  DPI Architecture  . . . . . . . . . . . . . . . . . . . . .  6
     3. SNMP DPI PROTOCOL . . . . . . . . . . . . . . . . . . . . .   10
     3.1  Connection Establishment  . . . . . . . . . . . . . . . .   10
     3.1.1  SNMP PDU to GET the Agent's DPI port  . . . . . . . . .   11
     3.1.2  SNMP PDU Containing the RESPONSE to the GET   . . . . .   13
     3.2  SNMP DPI Packet Formats   . . . . . . . . . . . . . . . .   15
     3.2.1  DPI Packet Header   . . . . . . . . . . . . . . . . . .   15
     3.2.2  OPEN  . . . . . . . . . . . . . . . . . . . . . . . . .   16
     3.2.3  CLOSE   . . . . . . . . . . . . . . . . . . . . . . . .   18
     3.2.4  ARE_YOU_THERE   . . . . . . . . . . . . . . . . . . . .   19
     3.2.5  REGISTER  . . . . . . . . . . . . . . . . . . . . . . .   20
     3.2.6  UNREGISTER  . . . . . . . . . . . . . . . . . . . . . .   22
     3.2.7  GET   . . . . . . . . . . . . . . . . . . . . . . . . .   23
     3.2.8  GETNEXT   . . . . . . . . . . . . . . . . . . . . . . .   24
     3.2.9  GETBULK   . . . . . . . . . . . . . . . . . . . . . . .   25
     3.2.10  SET, COMMIT and UNDO   . . . . . . . . . . . . . . . .   26
     3.2.11  RESPONSE   . . . . . . . . . . . . . . . . . . . . . .   29
     3.2.12  TRAP   . . . . . . . . . . . . . . . . . . . . . . . .   31
     3.3  Constants and Values  . . . . . . . . . . . . . . . . . .   33



Wijnen, Carpenter, Curran, Sehgal & Waters                      [Page 1]

RFC 1592 SNMP-DPI March 1994 3.3.1 Protocol Version and Release Values . . . . . . . . . 33 3.3.2 Packet Type Values . . . . . . . . . . . . . . . . . . 34 3.3.3 Variable Type Values . . . . . . . . . . . . . . . . . 35 3.3.4 Value Representation . . . . . . . . . . . . . . . . . 36 3.3.5 Character set selection . . . . . . . . . . . . . . . 36 3.3.6 Error Code Values for SNMP DPI RESPONSE packets . . . 37 3.3.7 UNREGISTER Reason Codes . . . . . . . . . . . . . . . 40 3.3.8 CLOSE Reason Codes . . . . . . . . . . . . . . . . . . 41 4. DPI 2.0 MIB DEFINITION . . . . . . . . . . . . . . . . . . 41 5. SUBAGENT CONSIDERATIONS . . . . . . . . . . . . . . . . . . 42 5.1 DPI API . . . . . . . . . . . . . . . . . . . . . . . . 43 5.2 Overview of Request Processing . . . . . . . . . . . . . 44 5.2.1 GET Processing . . . . . . . . . . . . . . . . . . . . 44 5.2.2 SET Processing . . . . . . . . . . . . . . . . . . . . 44 5.2.3 GETNEXT Processing . . . . . . . . . . . . . . . . . . 46 5.2.4 GETBULK Processing . . . . . . . . . . . . . . . . . . 47 5.2.5 OPEN Request . . . . . . . . . . . . . . . . . . . . . 48 5.2.6 CLOSE Request . . . . . . . . . . . . . . . . . . . . 49 5.2.7 REGISTER Request . . . . . . . . . . . . . . . . . . . 49 5.2.8 UNREGISTER Request . . . . . . . . . . . . . . . . . . 50 5.2.9 TRAP Request . . . . . . . . . . . . . . . . . . . . . 51 5.2.10 ARE_YOU_THERE request . . . . . . . . . . . . . . . . 51 5.2.11 How to query the DPI port. . . . . . . . . . . . . . 51 6. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . 51 7. SECURITY CONSIDERATIONS . . . . . . . . . . . . . . . . . . 52 8. AUTHORS' ADDRESSES . . . . . . . . . . . . . . . . . . . . 53 9. SAMPLE SOURCES FOR ANONYMOUS FTP . . . . . . . . . . . . . 54 1. INTRODUCTION This RFC describes version 2.0 of a protocol that International Business Machines Corporation (IBM) has been implementing in most of its SNMP agents to allow dynamic extension of supported MIBs. Bell Northern Research (BNR) has also implemented a version of this protocol in some of its SNMP agents for the same reason. The Simple Network Management Protocol (SNMP [1]) Distributed Protocol Interface (DPI) is an extension to SNMP agents that permits end-users to dynamically add, delete or replace management variables in the local Management Information Base without requiring recompilation of the SNMP agent. This is achieved by writing a so- called sub-agent that communicates with the agent via the SNMP-DPI. For the author of a sub-agent, the SNMP-DPI eliminates the need to know the details of ASN.1 [2] or SNMP PDU (Protocol Data Unit) encoding/decoding [1, 3]. Versions 1.0 and 1.1 of this protocol have been in use within IBM Wijnen, Carpenter, Curran, Sehgal & Waters [Page 2]
RFC 1592 SNMP-DPI March 1994 since 1989 and is included in the SNMP agents for VM, MVS and OS/2. Version 1.2 of this protocol has been in use within BNR since 1992. 1.1 MOTIVATION The Simple Network Management Protocol [1] defines a protocol that permits operations on a collection of variables. This set of variables is called the Management Information Base (MIB) and a core set of variables has previously been defined [4, 5]; however, the design of the MIB makes provision for extension of this core set. Thus, an enterprise or individual can define variables of their own which represent information of use to them. An example of a potentially interesting variable which is not in the core MIB would be CPU utilization (percent busy). Unfortunately, conventional SNMP agent implementations provide no means for an end-user to make available new variables. Besides this, today there are many MIBs that people want to implement on a system. Without a capability for sub-agents, this requires all the MIBs to be implemented in one big monolithic agent, which is in many cases undesirable. The SNMP DPI addresses these issues by providing a light-weight mechanism by which a process can register the existence of a MIB variable or a MIB sub-tree with the SNMP agent. Requests for the variable(s) that are received by the SNMP agent are passed to the process acting as a sub-agent. The sub-agent then returns an appropriate answer to the SNMP agent. The SNMP agent eventually packages an SNMP response packet and sends the answer back to the remote network management station that initiated the request. Remote network management stations have no knowledge that the SNMP agent calls on other processes to obtain an answer. As far as they can tell, there is only one network management application (agent) running on the host. At the San Diego IETF (March 1992) a BOF was held on multiplexing SNMP agent's requirements. Both the SMUX [6] and DPI [7] protocols were discussed, as well as other unpublished approaches. There was also discussion regarding a need for a standard for multiplexing SNMP agents or sub-agent support. At the end of the BOF, however, there was not enough support for defining a standard. This was due, at least partially, to a few well known SNMP authors who stated that the proxy and party support for SNMPv2 (SMP at the time) would solve the problem. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 3]
RFC 1592 SNMP-DPI March 1994 Nevertheless, questions continue to be raised about sub-agent support (both in SNMP and SNMP2 mail lists) in spite of both SNMPv2 [8] being on the standard's track and SMUX being changed to a historic RFC. Furthermore, within IBM and BNR we continue to see a substantial and expanding use of the DPI protocol. with positive results. Therefore, we believe that there is a place for a sub-agent protocol and we again offer this new version as an experimental protocol. We encourage people to try it and send us feedback. Depending on that feedback, we may decide to try to get onto the standards track at a later time. During discussions about sub-agent interfaces at the San Diego BOF it also became clear that we should reduce the focus on the API for the sub-agent programmers. This RFC, therefore, specifies only the protocol to distribute SNMP requests from the main SNMP agent to the sub-agents. Programmers can build one or more Programming APIs on top of that protocol as needed, and sample API code is available from the authors of this document. 1.2 SUMMARY OF CHANGES The following changes have been made since the initial definition of SNMP-DPI [7]. Some of these resulted from comparing the SMUX [6] and DPI [7] protocols. o Documentation changes to cleanup and be more specific in some areas. Among other things, this includes: - Defining that integers are in network byte order - Defining the character set used for strings - Defining how DisplayStrings are handled. - Including DPI20 MIB definition. o Removal of the Programming API from the document. o Addition of new DPI packet types: - SNMP_DPI_OPEN for a sub-agent to open a "connection" with the DPI SNMP capable agent. The sub-agent must now identify itself and optionally provide a "password" for the connection. - SNMP_DPI_CLOSE for the agent or sub-agent to close the connection in a graceful way. - SNMP_DPI_ARE_YOU_THERE for the sub-agent to verify that the agent still knows about the sub-agent. - SNMP_DPI_UNREGISTER for the agent or sub-agent to terminate the registration of a MIB variable or MIB sub-tree. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 4]
RFC 1592 SNMP-DPI March 1994 - SNMP_DPI_COMMIT which instructs the sub-agent to actually commit a previous SNMP_DPI_SET request. This, together with the UNDO, allows DPI sub-agents to be compliant with SNMP in the sense that we can now handle the "as if simultaneous" requirement. - SNMP_DPI_UNDO which instructs the sub-agent to UNDO a SET or COMMIT if such is needed. o Changes to DPI packets: - Multiple varBinds can now be exchanged in one DPI packet (for GET, GETNEXT, SET, TRAP). The sub-agent can specify the maximum it wants to handle per packet. - The packet headers now contain a packet-ID (similar to SNMP request ID in SNMP PDU). This allows to match RESPONSE packets to REQUESTS, which is important for UDP based DPI-connections. - The SNMP_DPI_REGISTER packet has new fields for time_out and for requested priority. - The SNMP_DPI_TRAP packet allows to specify an enterprise OID. In addition, the generic and specific trap types are now 4 octets, so that we can pass the types correctly. - In general, the packets have a more consistent layout. o The agent now sends a RESPONSE to a REGISTER request o Addition of SNMPv2 error codes and value types. 2. THEORY OF OPERATION 2.1 CONNECTION ESTABLISHMENT AND TERMINATION Communication between the SNMP Agent and its clients (sub-agents) takes place via a communication mechanism. The communication type can be either a logical stream connection (via TCP, for instance) or an unreliable datagram connection (UDP, for instance). It should be noted that other stream oriented transport communication mechanisms can also be used. For example, the VM SNMP agent allows DPI connections over IUCV (Inter-User Communications Vehicle) [9, 10]. Other than the connection establishment procedure, the protocol used is identical in these environments. In Unix the number of processes is limited by the number of file- descriptors that can be opened. Since each TCP socket represents a file-descriptor, restricting SNMP-DPI protocol to TCP only connections would limit the number of sub-agents an agent could support. As a result, the some SNMP-DPI agents support both TCP and UDP socket type communication mechanisms for the SNMP-DPI protocol. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 5]
RFC 1592 SNMP-DPI March 1994 Please note that in the following portion of this text the SNMP-DPI agent is referred simply as the agent. Once the transport connection has been set up, the sub-agent must also initialize the logical connection with the agent. To do so it issues an OPEN request to the agent in which the sub-agent uniquely identifies itself and passes some other parameters to the agent, such as, the maximum number of varBinds per interaction it is prepared to handle, and the timeout the agent should use when waiting for a response from the sub-agent. When the sub-agent prepares to stop or cease operations, it first issues a CLOSE to shut down the logical connection with the agent, and then closes the transport connection. 2.2 REGISTRATION A sub-agent supports a collection of MIB variables or object identifiers (object IDs) that constitute its MIB (sub)tree. Each of these object IDs consists of a group ID and an instance ID. The group ID is the root of the sub-agent's MIB tree that it supports and the point of registration to the agent's MIB tree. The instance ID is the piece of the Object Identifier that follows the group ID (registration point), so it is not an instance in the terms of the SNMP definition of an instance. Regardless of the transport mechanism used, after establishing a connection to the agent, the sub-agent registers a branch (group ID) to the Agent's MIB tree. With the registration request, the sub- agent passes some parameters, such as, requested priority and a timeout value for this specific sub-tree. The agent sends back a response to indicate success or failure of the registration request. 2.3 NORMAL OPERATION Once the sub-agent has set up both the physical and logical connection to the agent, and once it has successfully registered the sub-tree(s) of the MIB(s) that it supports, it waits for requests from the SNMP agent or generates traps as required. 2.4 DPI ARCHITECTURE These are the requests that can be initiated by the SNMP agent: GET, GETNEXT, GETBULK, SET, COMMIT, UNDO, UNREGISTER, and CLOSE. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 6]
RFC 1592 SNMP-DPI March 1994 The first four of these correspond directly to SNMP requests that a network management station can make (By default a GETBULK request will be translated into multiple GETNEXT requests by the agent, but a sub-agent may request that the GETBULK be passed to it). The COMMIT, UNDO, UNREGISTER, ARE_YOU_THERE and CLOSE requests are specific SNMP-DPI requests. The sub-agent normally responds to a request with a RESPONSE packet. The CLOSE request is an exception for which the sub-agent only closes the physical connection. These are the requests that can be initiated by a sub-agent: OPEN, REGISTER, TRAP, UNREGISTER, ARE_YOU_THERE and CLOSE. The agent responds to OPEN, REGISTER, UNREGISTER and ARE_YOU_THERE with a RESPONSE packet. The TRAP packet is just accepted and forwarded by the agent without returning any information to the sub- agent. The CLOSE packet is also just accepted by the agent upon which it closes the physical connection. See Figure 1 for an overview of the DPI packet flow. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 7]
RFC 1592 SNMP-DPI March 1994 ------------------------------------------------------------------- *---------------------------------* | | | SNMP Network | | Management Station | | | |---------------------------------| | SNMP Protocol | *---------------------------------* A | Get A | | GetNext | GetResponse Trap | | GetBulk | | | Set | | V | *------------------------------* *-------------------* | SNMP Protocol | | DPI Interface | |------------------------------| Response | *--------------| | | |<----------->| | | | | | | | | | SNMP Agent | | | | | | | | Get,GetNext | | | | | | (GetBulk) | | Client | | | | Set,Commit | | | | A *-----------+-> | Undo | | | | | | Get/Set | |------------>| | or | | Trap| | info | | | | | | | | | SNMP | | | | |-----+-----+-------* | | trap | | SNMP | | | V | | DPI |<------------| | Sub-Agent | | | | | | | | | Statically Linked | | | | | | | Instrumentation | | | | | | | (like MIB II) | | | | | | | | | | close | | | | A | | | unregister | | | |-------+-----------| | |<----------->| | | | V | | | | | | | | | | | | | | | | | AreYouThere | | | | TCP/IP layers | | | open | | | | Kernel | | | register | | | | | | |<------------| | | *------------------------------* *-------------------* ------------------------------------------------------------------- Figure 1. SNMP DPI overview Wijnen, Carpenter, Curran, Sehgal & Waters [Page 8]
RFC 1592 SNMP-DPI March 1994 Remarks for Figure 1: o The SNMP agent communicates with the SNMP manager via the standard SNMP protocol. o The SNMP agent communicates with some statically linked-in instrumentation (potentially for the MIB II), which in turn talks to the TCP/IP layers and kernel (operating system) in an implementation-dependent manner. o An SNMP sub-agent, running as a separate process (potentially on another machine), can set up a connection with the agent. The sub-agent has an option to communicate with the SNMP agent through UDP or TCP sockets, or even through other mechanisms. o Once the connection is established, the sub-agent issues a DPI OPEN and one or more REGISTER requests to register one or more MIB sub-trees with the SNMP agent. o The SNMP agent responds to DPI OPEN and REGISTER requests with a RESPONSE packet, indicating success or failure. o The SNMP agent will decode SNMP packets. If such a packet contains a Get or GetNext request for an object in a sub-tree registered by a sub-agent, it sends a corresponding DPI packet to the sub-agent. If the request is for a GetBulk, then the agent translates it into multiple DPI GETNEXT packets and sends those to the sub-agent. However, the sub-agent can request (in the REGISTER packet) that a GETBULK be passed to the sub-agent. If the request is for a Set, then the agent uses a 2-phase commit scheme and sends the sub-agent a sequence of SET/COMMIT, SET/UNDO or SET/COMMIT/UNDO DPI packets. o The SNMP sub-agent sends responses back via a RESPONSE packet. o The SNMP agent then encodes the reply into an SNMP packet and sends it back to the requesting SNMP manager. o If the sub-agent wants to report an important state change, it sends a DPI TRAP packet to the SNMP agent which will encode it into an SNMP trap packet and send it to the manager(s). o If the sub-agent wants to stop operations, it sends a DPI UNREGISTER and a DPI CLOSE packet to the agent. The agent sends a response to an UNREGISTER request. o There is no RESPONSE to a CLOSE, the agent just closes the DPI connection. A CLOSE implies an UNREGISTER for all registrations that exist for the DPI connection being CLOSED. o An agent can send DPI UNREGISTER (if a higher priority registration comes in or for other reasons) to the sub-agent, the sub-agent then responds with a DPI RESPONSE packet. o An agent can also (for whatever reason) send a DPI CLOSE to indicate it is terminating the DPI connection. o A sub-agent can send an ARE_YOU_THERE to verify that the "connection" is still open. If so, the agent sends a RESPONSE with no error, otherwise, it may send a RESPONSE with an error Wijnen, Carpenter, Curran, Sehgal & Waters [Page 9]
RFC 1592 SNMP-DPI March 1994 indication, or not react at all. 3. SNMP DPI PROTOCOL This section describes the actual protocol used between the SNMP agent and sub-agents. 3.1 CONNECTION ESTABLISHMENT In a TCP/IP environment, the SNMP agent listens on an arbitrary TCP/UDP port for a connection request from a sub-agent. It is important to realize that a well-known port is not used: every invocation of the SNMP agent will potentially result in a different TCP/UDP port being used. A sub-agent needs to determine this port number to establish a connection. The sub-agent learns the port number from the agent by sending it one conventional SNMP get-request PDU. The port numbers are maintained by the SNMP agent as the objects whose identifiers are: 1.3.6.1.4.1.2.2.1.1.0 dpiPort.0 (old DPI 1.x form) 1.3.6.1.4.1.2.2.1.1.1.0 dpiPortForTCP.0 1.3.6.1.4.1.2.2.1.1.2.0 dpiPortForUDP.0 These variables are registered under the IBM enterprise-specific tree. See 4, "DPI 2.0 MIB definition" for more information. The SNMP agent replies with a conventional SNMP response PDU that contains the port number to be used. This response is examined by the sub-agent and the port number is extracted. The sub-agent then establishes the connection to the specified port. On the surface, this procedure appears to mean that the sub-agent must be able to create and parse SNMP packets, but this is not the case. A DPI Application Programming Interface (API) normally provides a library routine, query_DPI_port(), which can be used to generate and parse the required SNMP packets. This very small routine (under 100 lines of C), does not greatly increase the size of any sub-agent. NOTE: Since this RFC does not define an API, the actual code of and interface to a query_DPI_port() type of function depends on the implementation. For completeness, byte-by-byte descriptions of the packets to be generated by an SNMP DPI API routine query_DPI_port() are provided below. This is probably of little interest to most readers and reading the source of a query_DPI_port() function provides much of Wijnen, Carpenter, Curran, Sehgal & Waters [Page 10]
RFC 1592 SNMP-DPI March 1994 the same information. 3.1.1 SNMP PDU TO GET THE AGENT'S DPI PORT As noted, before a TCP/UDP connection to the SNMP agent can be made, the sub-agent must learn which port that the agent is listening on. To do so, it can issue an SNMP GET for the variable dpiPortForTCP.0 (1.3.6.1.4.1.2.2.1.1.1.0) or variable dpiPortForUDP.0 (1.3.6.1.4.1.2.2.1.1.2.0). The SNMP PDU can be constructed as shown below. This PDU must be sent to UDP port 161 on the host where the agent runs (probably the same host where the sub-agent runs). The (SNMPv1) packet shown below is for the TCP port. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 11]
RFC 1592 SNMP-DPI March 1994 +-----------------------------------------------------------------+ | Table 1 (Page 1 of 2). SNMP GET PDU for dpiPortForTCP.0 | +---------------+----------------+--------------------------------+ | OFFSET | VALUE | FIELD | +---------------+----------------+--------------------------------+ | 0 | 0x30 | ASN.1 header | +---------------+----------------+--------------------------------+ | 1 | 37 + len | PDU_length, see formula below | +---------------+----------------+--------------------------------+ | 2 | 0x02 0x01 0x00 | SNMP version: | | | | (integer,length=1,value=0) | +---------------+----------------+--------------------------------+ | 5 | 0x04 | community name (string) | +---------------+----------------+--------------------------------+ | 6 | len | length of community name | +---------------+----------------+--------------------------------+ | 7 | community name | varies | +---------------+----------------+--------------------------------+ | 7 + len | 0xa0 0x1c | SNMP GET request: | | | | request_type=0xa0,length=0x1c | +---------------+----------------+--------------------------------+ | 7 + len + 2 | 0x02 0x01 0x01 | SNMP request ID: | | | | integer,length=1,ID=1 | +---------------+----------------+--------------------------------+ | 7 + len + 5 | 0x02 0x01 0x00 | SNMP error status: | | | | integer,length=1,error=0 | +---------------+----------------+--------------------------------+ | 7 + len + 8 | 0x02 0x01 0x00 | SNMP index: | | | | integer,length=1,index=0 | +---------------+----------------+--------------------------------+ | 7 + len + 11 | 0x30 0x11 | varBind list, length=0x11 | +---------------+----------------+--------------------------------+ | 7 + len + 13 | 0x30 0x0f | varBind, length=0x0f | +---------------+----------------+--------------------------------+ | 7 + len + 15 | 0x06 0x0b | Object ID, length=0x0b | +---------------+----------------+--------------------------------+ Wijnen, Carpenter, Curran, Sehgal & Waters [Page 12]
RFC 1592 SNMP-DPI March 1994 +-----------------------------------------------------------------+ | Table 1 (Page 2 of 2). SNMP GET PDU for dpiPortForTCP.0 | +---------------+----------------+--------------------------------+ | OFFSET | VALUE | FIELD | +---------------+----------------+--------------------------------+ | 7 + len + 17 | 0x2b 0x06 0x01 | Object-ID: | | | 0x04 0x01 0x02 | 1.3.6.1.4.1.2.2.1.1.1 | | | 0x02 0x01 0x01 | Object-instance: 0 | | | 0x01 0x00 | | +---------------+----------------+--------------------------------+ | 7 + len + 28 | 0x05 0x00 | null value, length=0 | +---------------+----------------+--------------------------------+ | NOTE: Formula to calculate "PDU_length": | | | | PDU_length = length of version field and string tag (4 bytes)| | + length of community length field (1 byte) | | + length of community name (depends...) | | + length of SNMP GET request (32 bytes) | | | | = 37 + length of community name | +-----------------------------------------------------------------+ 3.1.2 SNMP PDU CONTAINING THE RESPONSE TO THE GET Assuming that no errors occurred, the port is returned in the last few octets of the received packet. In the simple case, where the port number will be between 1024 and 16,385, the format of the packet is shown below. Note: In practice, the port number can be any positive number in the range from 1 through 65,535. A port number of 0 means that the agent does not have a dpiPort defined for the requested protocol. So the actual port value maybe in the last 1, 2 or 3 octets. The sample implementation code shows how to handle the response to cover all those cases, including error conditions. Note: The (SNMPv1) packet shown below is for the TCP port. +-----------------------------------------------------------------+ | Table 2 (Page 1 of 3). SNMP RESPONSE PDU for dpiPortForTCP.0 | +---------------+----------------+--------------------------------+ | OFFSET | VALUE | FIELD | +---------------+----------------+--------------------------------+ | 0 | 0x30 | ASN.1 header | +---------------+----------------+--------------------------------+ | 1 | 39 + len | length, see formula below | +---------------+----------------+--------------------------------+ Wijnen, Carpenter, Curran, Sehgal & Waters [Page 13]
RFC 1592 SNMP-DPI March 1994 +-----------------------------------------------------------------+ | Table 2 (Page 2 of 3). SNMP RESPONSE PDU for dpiPortForTCP.0 | +---------------+----------------+--------------------------------+ | OFFSET | VALUE | FIELD | +---------------+----------------+--------------------------------+ | 2 | 0x02 0x01 0x00 | version | | | | (integer,length=1,value=0) | +---------------+----------------+--------------------------------+ | 5 | 0x04 | community name (string) | +---------------+----------------+--------------------------------+ | 6 | len | length of community name | +---------------+----------------+--------------------------------+ | 7 | community name | | +---------------+----------------+--------------------------------+ | 7 + len | 0xa2 0x1e | SNMP RESPONSE: | | | | request_type=0xa2,length=0x1e | +---------------+----------------+--------------------------------+ | 7 + len + 2 | 0x02 0x01 0x01 | SNMP request ID: | | | | integer,length=1,ID=1 | +---------------+----------------+--------------------------------+ | 7 + len + 5 | 0x02 0x01 0x00 | SNMP error status: | | | | integer,length=1,error=0 | +---------------+----------------+--------------------------------+ | 7 + len + 8 | 0x02 0x01 0x00 | SNMP index: | | | | integer,length=1,index=0 | +---------------+----------------+--------------------------------+ | 7 + len + 11 | 0x30 0x13 | varBind list, length=0x13 | +---------------+----------------+--------------------------------+ | 7 + len + 13 | 0x30 0x11 | varBind, length=0x11 | +---------------+----------------+--------------------------------+ | 7 + len + 15 | 0x06 0x0b | Object ID, length=0x0b | +---------------+----------------+--------------------------------+ | 7 + len + 17 | 0x2b 0x06 0x01 | Object-ID: | | | 0x04 0x01 0x02 | 1.3.6.1.4.1.2.2.1.1.1 | | | 0x02 0x01 0x01 | Object-instance: 0 | | | 0x01 0x00 | | +---------------+----------------+--------------------------------+ | 7 + len + 28 | 0x02 0x02 | integer, length=2 | +---------------+----------------+--------------------------------+ | 7 + len + 30 | MSB LSB | port number (MSB, LSB) | +---------------+----------------+--------------------------------+ Wijnen, Carpenter, Curran, Sehgal & Waters [Page 14]
RFC 1592 SNMP-DPI March 1994 +-----------------------------------------------------------------+ | Table 2 (Page 3 of 3). SNMP RESPONSE PDU for dpiPortForTCP.0 | +---------------+----------------+--------------------------------+ | NOTE: Formula to calculate "PDU_length": | | | | PDU_length = length of version field and string tag (4 bytes)| | + length of community length field (1 byte) | | + length of community name (depends...) | | + length of SNMP RESPONSE (34 bytes) | | | | = 39 + length of community name | +-----------------------------------------------------------------+ 3.2 SNMP DPI PACKET FORMATS Each request to, or response from, the agent or sub-agent is constructed as a "packet" and is written to the stream. Each packet is prefaced with the length of the data remaining in the packet. The length is stored in network byte order, the most significant byte (MSB) first, least significant byte (LSB) last. If we consider a stream connection (like TCP), the receiving side will read the packet by doing something similar to: unsigned char len_bfr[2]; unsigned char *bfr; int len; read(fd,len_bfr,2); len = len_bfr[0] * 256 + len_bfr[1]; bfr = malloc(len); read(fd,bfr,len); Note: The above example makes no provisions for error handling or a read returning less than the requested amount of data,and it is not intended to be used literally. 3.2.1 DPI PACKET HEADER The first part of every packet identifies the application protocol being used as well as some version information. The protocol major version is intended to indicate, in broad terms, what version of the protocol is used. The protocol minor version is intended to identify major incompatible versions of the protocol. The protocol release is intended to indicate incremental modifications to the protocol. The constants that are valid for these fields are defined in Table 15. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 15]
RFC 1592 SNMP-DPI March 1994 The next field, present in all packets, is the packet ID. It contains packet identification that can help an agent or sub-agent match responses with request. This is useful with UDP connections over which packets can be lost. The packet ID is a monotonically increasing unsigned 16-bit integer which wraps at its maximum value. The next field, present in all packets, is the packet type. It indicates what kind of packet we're dealing with (OPEN, REGISTER, GET, GETNEXT, GETBULK, SET, COMMIT, UNDO, TRAP, RESPONSE, UNREGISTER, or CLOSE). The permitted values for this field are defined in Table 16 +-----------------------------------------------------------------+ | Table 3. SNMP DPI packet header. Present in all packets. | +------------+----------------------------------------------------+ | OFFSET | FIELD | +------------+----------------------------------------------------+ | 0 | packet length to follow (MSB to LSB) | +------------+----------------------------------------------------+ | 2 | protocol major version | +------------+----------------------------------------------------+ | 3 | protocol minor version | +------------+----------------------------------------------------+ | 4 | protocol release | +------------+----------------------------------------------------+ | 5 | packet id (MSB to LSB) | +------------+----------------------------------------------------+ | 7 | packet type | +------------+----------------------------------------------------+ From this point onwards, the contents of the packet are defined by the protocol being used. The remainder of this section describes: o Layout of packets for the SNMP DPI protocol, version 2.0. o Constants as defined with this version of the protocol. 3.2.2 OPEN In order for a sub-agent to communicate with a DPI capable SNMP agent, it must first send an SNMP DPI OPEN request to the agent to setup the "connection" with that agent. Such a packet contains the standard SNMP DPI header plus OPEN specific data. This data consists of: Wijnen, Carpenter, Curran, Sehgal & Waters [Page 16]
RFC 1592 SNMP-DPI March 1994 o a timeout value (in seconds). This is a requested timeout value to be used for all requests for objects for which there is no timeout value specified for the sub-tree under which the object is registered. If you specify a zero timeout value, then the agent will use its own default timeout value. If you want a larger value than the default value, then you can specify it here. However, the agent may have a maximum value that you can never exceed. If you do ask for a larger timeout than that maximum, the agent will set it at the maximum it accepts. o the maximum number of varBinds per DPI packet that the sub-agent is prepared to handle. o Selected character set to be used for the representation of the OBJECT ID strings and DisplayStrings. The choices are the native character set (0) or the ASCII character set (1). See 3.3.5, "Character set selection" for more information in character set selection. An agent may choose to support only the native character set. o null terminated sub-agent ID, which is a unique ASN.1 OBJECT identifier, so in dotted ASN.1 notation. This string is represented in the selected character set. o null terminated sub-agent description, which is a DisplayString describing the sub-agent. This string is represented in the selected character set. This may be the null-string if there is no description. o optionally a password that the agent uses to validate the sub-agent. It depends on the agent implementation if a password is required. If no password is passed, the length must be specified as zero. The sub-agent must expect a response indicating success or failure. See Table 19 for the valid codes in a DPI RESPONSE to a DPI OPEN request. If the error_code in the RESPONSE is not SNMP_ERROR_DPI_noError, then the agent closes the connection. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 17]
RFC 1592 SNMP-DPI March 1994 +-----------------------------------------------------------------+ | Table 4. Layout SNMP DPI OPEN packet | +------------+----------------------------------------------------+ | OFFSET | FIELD | +------------+----------------------------------------------------+ | 0 | packet length to follow (MSB to LSB) | +------------+----------------------------------------------------+ | 2 | protocol major version | +------------+----------------------------------------------------+ | 3 | protocol minor version | +------------+----------------------------------------------------+ | 4 | protocol release | +------------+----------------------------------------------------+ | 5 | packet id (MSB to LSB) | +------------+----------------------------------------------------+ | 7 | packet type = SNMP_DPI_OPEN | +------------+----------------------------------------------------+ | 8 | requested overall timeout (seconds, MSB to LSB) | +------------+----------------------------------------------------+ | 10 | max varBinds per DPI packet (MSB to LSB) | +------------+----------------------------------------------------+ | 12 | Selected character set (0=Native, 1=ASCII) | +------------+----------------------------------------------------+ | 13 | null terminated sub-agent ID (OID) | +------------+----------------------------------------------------+ | 13+L1 | null terminated sub-agent Description | +------------+----------------------------------------------------+ | 13+L2 | password length (zero if no password, MSB to LSB) | +------------+----------------------------------------------------+ | 15+L2 | password (if any) | +------------+----------------------------------------------------+ | NOTE: | | | | o L1 = strlen(sub-agent ID) + 1 | | o L2 = L1 + strlen(sub-agent Description) + 1 | | o OID and Description strings use selected character set | +-----------------------------------------------------------------+ 3.2.3 CLOSE In order for a sub-agent to close the "connection" with the DPI capable SNMP agent, it must send an SNMP DPI CLOSE request to the agent. The agent will not send a response, but closes the physical connection and implicitly unregisters any sub-trees related to the connection. An agent may also send to the sub-agent an SNMP DPI CLOSE packet that contains the standard SNMP DPI header plus CLOSE specific data. This Wijnen, Carpenter, Curran, Sehgal & Waters [Page 18]
RFC 1592 SNMP-DPI March 1994 data consists of: o a reason code for closing. See Table 21 for a list of valid reason codes. +-----------------------------------------------------------------+ | Table 5. Layout SNMP DPI CLOSE packet | +------------+----------------------------------------------------+ | OFFSET | FIELD | +------------+----------------------------------------------------+ | 0 | packet length to follow (MSB to LSB) | +------------+----------------------------------------------------+ | 2 | protocol major version | +------------+----------------------------------------------------+ | 3 | protocol minor version | +------------+----------------------------------------------------+ | 4 | protocol release | +------------+----------------------------------------------------+ | 5 | packet id (MSB to LSB) | +------------+----------------------------------------------------+ | 7 | packet type = SNMP_DPI_CLOSE | +------------+----------------------------------------------------+ | 8 | reason code (1 octet) | +------------+----------------------------------------------------+ 3.2.4 ARE_YOU_THERE An ARE_YOU_THERE packet allows a sub-agent to determine if it still has a DPI connection with the agent. This packet is necessary because a sub-agent passively awaits requests from an agent and normally will not detect problems with an agent connection in a timely manner. (In contrast, an agent becomes aware of any sub-agent connection problem in a timely manner because it sets a timeout when sending request). A sub-agent can send a SNMP DPI ARE_YOU_THERE packet to an agent which will then return a RESPONSE with a zero error code and a a zero error index if the connection is healthy. Otherwise, the agent may return a RESPONSE with an error indication. If the connection is broken, the sub-agent will see no response at all. An ARE_YOU_THERE packet contains the standard SNMP DPI header with no additional data. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 19]
RFC 1592 SNMP-DPI March 1994
RFC 1592 SNMP-DPI March 1994 the sub-agent returns. 5.2.9 TRAP REQUEST A sub-agent can request that the SNMP agent generates a trap for it. The sub-agent must provide the desired values for the generic and specific parameters of the trap. It may optionally provide a set of one or more name/type/length/value tuples that will be included in the trap packet. Also, it may optionally specify an Enterprise ID (Object Identifier) for the trap to be generated. If a NULL value is specified for the Enterprise ID, then the agent will use the sub- agent Identifier (from the DPI OPEN packet) as the Enterprise ID to be sent with the trap. 5.2.10 ARE_YOU_THERE REQUEST A sub-agent can send an ARE_YOU_THERE packet to the agent. This may be useful to do if you have a DPI "connection" over an unreliable transport protocol (like UDP). If the "connection" is in a healthy state, the agent responds with a RESPONSE packet with SNMP_ERROR_DPI_noError. If the "connection" is not in a healthy state, the agent may respond with a RESPONSE packet with an error indication, but the agent might not react at all, so you would timeout while waiting for a response. 5.2.11 HOW TO QUERY THE DPI PORT. The DPI API implementations are encouraged to provide a facility that helps DPI sub-agent programmers to dynamically find the port that the agent is using for the TCP and/or UDP DPI port(s). A suggested name for such a function is: query_DPI_port(). 6. REFERENCES [1] Case, J., Fedor, M., Schoffstall M., and J. Davin, "Simple Network Management Protocol (SNMP)", STD 15, RFC 1157, SNMP Research, Performance Systems International, MIT Laboratory for Computer Science, May 1990. [2] Information processing systems - Open Systems Interconnection, "Specification of Abstract Syntax Notation One (ASN.1)", International Organization for Standardization, International Standard 8824, December 1987. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 51]
RFC 1592 SNMP-DPI March 1994 [3] Information processing systems - Open Systems Interconnection, "Specification of Basic Encoding Rules for Abstract Syntax Notation One (ASN.1)", International Organization for Standardization, International Standard 8825, December 1987. [4] McCloghrie, K., and M. Rose, "Management Information Base for Network Management of TCP/IP-based internets: MIB II", STD 17, RFC 1213, Hughes LAN Systems, Performance Systems International, March 1991. [5] Rose, M., and K. McCloghrie, "Structure and Identification of Management Information for TCP/IP-based internets", STD 16, RFC 1155, Performance Systems International, Hughes LAN Systems, May 1990 [6] Rose, M., "SNMP MUX Protocol and MIB", RFC 1227, Performance Systems International, RFC 1227, May 1991. [7] Carpenter G., and B. Wijnen, "SNMP-DPI, Simple Network Management Protocol Distributed Program Interface", RFC 1228, International Business Machines, Inc., May 1991. [8] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "SNMPv2 RFCs (RFC 1441 through RFC 1452)", SNMP Research Inc, Hughes LAN Systems, Dover Beach Consulting Inc, Carnegie Mellon University, Trusted Information Systems, April 1993. [9] International Business Machines, Inc., TCP/IP for VM: Programmer's Reference, SC31-6084-0, 1990. [10] International Business Machines, Inc., Virtual Machine System Facilities for Programming, Release 6, SC24-5288-01, 1988. 7. SECURITY CONSIDERATIONS Security issues are not discussed in this memo. Wijnen, Carpenter, Curran, Sehgal & Waters [Page 52]
RFC 1592 SNMP-DPI March 1994 8. AUTHORS' ADDRESSES Bert Wijnen IBM International Operations Watsonweg 2 1423 ND Uithoorn The Netherlands Phone: +31-2975-53316 Fax: +31-2975-62468 EMail: wijnen@vnet.ibm.com Geoffrey C. Carpenter IBM T.J. Watson Research Center P.O. Box 218 Yorktown Heights, NY 10598 USA Phone: +1-914-945-1970 EMail: gcc@watson.ibm.com Kim Curran Bell Northern Research Ltd. P.O. Box 3511 Station C Ottawa, Ontario K1Y 4HY Canada Phone: +1-613-763-5283 EMail: kcurran@bnr.ca Aditya Sehgal Bell Northern Research Ltd. P. O. Box 3511 Station C Ottawa, Ontario K1Y 4HY Canada Phone: +1-613-763-8821 EMail: asehgal@bnr.ca Wijnen, Carpenter, Curran, Sehgal & Waters [Page 53]
RFC 1592 SNMP-DPI March 1994 Glen Waters Bell Northern Research Ltd. P.O. Box 3511 Station C Ottawa, Ontario K1Y 4HY Canada Phone: +1-613-763-3933 EMail: gwaters@bnr.ca



Back to RFC index

 

Associates:

 



Sponsered-Sites:

Register domain name and transfer | Cheap webhosting service | Domain name registration

 

 

""