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Internet Draft HTTP-based SNMP and CMIP Network Management Nov. 19, 1996 |
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HTTP-based SNMP and CMIP Network Management |
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Luca Deri |
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IBM Zurich Research Laboratory |
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lde@zurich.ibm.com |
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November 19, 1996 |
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Status of this Memo |
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This document is an Internet-Draft. Internet-Drafts are working |
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documents of the Internet Engineering Task Force (IETF), its areas, |
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and its working groups. Note that other groups may also distribute |
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working documents as Internet-Drafts. |
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Internet-Drafts are draft documents valid for a maximum of six months |
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and may be updated, replaced, or obsoleted by other documents at any |
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time. It is inappropriate to use Internet-Drafts as reference material |
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or to cite them other than as ''work in progress.'' |
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To learn the current status of any Internet-Draft, please check the |
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''1id-abstracts.txt'' listing contained in the Internet-Drafts Shadow |
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Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), |
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munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or |
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ftp.isi.edu (US West Coast). |
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1. Abstract |
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This document describes the application of the HyperText Transfer |
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Protocol (HTTP) [HTTP] for the purpose of SNMP [SNMP] and CMIP [CMIP] |
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management. It shows how SNMP and CMIP resources can be managed by |
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using the standard HTTP protocol by defining a mapping between |
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SNMP/CMIP protocols and HTTP. The mapping is very simple and based on |
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strings which can easily be handled by any programming and scripting |
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language. This will allow light and simple HTTP-based applications to |
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be created, since they have not to include any management service like |
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encoding/decoding nor to handle complex data types. |
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This document does not cover management of HTTP [Hazewinkel]. |
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2. World Wide Web and Network Management |
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The World Wide Webarchitecture is depicted below: |
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------> |
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HTTP client HTTP HTTP Server |
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<------ |
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Figure 1: World Wide Web architecture |
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HTTP servers provide information which can be retrieved by WWW |
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browsers using the HTTP protocol. The HTTP protocol is a simple, |
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stateless information retrieval protocol based on TCP/IP. The |
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retrieved information can be specified in several formats including |
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graphics, text, binary and HTML (Hyper Text Markup Language) [HTML]. |
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Expires May 19, 1997 [Page 1] |
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Internet Draft HTTP-based SNMP and CMIP Network Management Nov. 19, 1996 |
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In order to manage network resources using HTTP it is necessary to |
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have an application which speaks both HTTP and SNMP/CMIP. This can be |
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achieved in two ways by: |
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1. extending standard HTTP servers |
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2. creating a proxy application which allows to issue SNMP/CMIP |
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protocol requests using HTTP. |
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The first solution has the following advantages: |
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1. it is relatively easy to implement since the HTTP server |
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transparently handles the HTTP protocol |
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2. existing character-based network management applications can |
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easily become Web-aware since it is straightforward to enrich |
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the textual output with HTML tags. |
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The second solution requires the implementation of the HTTP protocol |
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but it offers better performance. In fact, HTTP servers usually offer |
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standard interfaces such as CGI (Common Gateway Interface) which |
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allows external applications to be executed when a certain URL [URL] |
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(Uniform Resource Locator: a physical address of an object which is |
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retrievable using network protocols such as HTTP) is requested. Since |
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launching applications requires some system resources, the performance |
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is degraded proportionally to the complexity of the CGI application |
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that has to be executed. Apart from offering a better performance, |
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this second solution allows network events (SNMP traps and CMIP |
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notifications) to be handled without the need to rely on another |
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application. This is because the proxy can receive network events and |
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store them. In the case of a CGI-based solution, an external |
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application has to receive the network events which can then be |
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retrieved through a CGI application. |
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In both cases, users communicate with an HTTP application regardless |
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of the nature of this application, either HTTP server extended with |
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CGI applications or proxy. |
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3. URL Convention for SNMP/CMIP Management |
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In order to manage network resources using HTTP, a mapping between |
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management operations and URLs has to be defined. The proposed mapping |
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is compliant with the standard URL syntax and therefore it can be |
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handled by conventional HTTP servers and WWW browsers. The URL is |
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composed of 5 elements, |
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http://<host>/<protocol>/<operation>/<context>?<parameters>, where: |
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1. <host> identifies the host where the HTTP server runs; |
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2. <protocol> specifies the protocol used; |
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3. <operation> specifies the protocol operation; |
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4. <context> specifies the context to use, if any; |
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5. <parameters> contain the operation parameters, if any. |
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Expires May 19, 1997 [Page 2] |
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Internet Draft HTTP-based SNMP and CMIP Network Management Nov. 19, 1996 |
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Although this mapping is quite general and can be used for instance with |
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protocols like SQL, our interest focuses on SNMP and CMIP: |
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1. SNMPv1 |
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<protocol>: SNMP |
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<operation>: GET, GETNEXT, SET, WALK, TRAP(used to retrieve traps) |
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<context>: object identifier which identifies the MIB attribute |
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<parameters>: additional operation-dependent values (for instance the value |
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to be used for the SET) |
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2. CMIP |
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<protocol>: CMIP |
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<operation>: GET, SET, CREATE, DELETE, ACTION, EVR (used to retrieve |
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event reports) |
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<context>: Agent AE-Title/managed object instance |
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<parameters>: additional operation-dependent values (for instance the value |
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to be used for the SET) |
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Since this mapping is supposed to be used not only by software |
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applications (for instance CGI scripts) but also by human operators |
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from within their WWW browsers, it is very important to have a clean |
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and simple syntax. All the ASN.1 values have to be expressed in string |
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format and binary values (BER) are not allowed since they cannot be |
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handled by humans. The object identifiers contained inside the URL can |
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be both in numeric and symbolic form. |
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ASN.1 values for SNMP are fairly simple hence their conversion to |
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string is straightforward: |
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+------------------------------------------------------------------+ |
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| INTEGER | '1996' | |
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+------------------------------------------------------------------+ |
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| OCTET STRING | 'Luca' | |
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+------------------------------------------------------------------+ |
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| OBJECT IDENTIFIER | '1.3.6.1.2' or 'mgmt' | |
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+------------------------------------------------------------------+ |
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| IpAddress | '9.4.33.33' or 'kis.zurich.ibm.com' | |
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+------------------------------------------------------------------+ |
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| Counter32 | '4294967294' | |
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+------------------------------------------------------------------+ |
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| Gauge32 | '3265532231' | |
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+------------------------------------------------------------------+ |
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| TimeTicks | '2645533545' | |
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+------------------------------------------------------------------+ |
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| Opaque | '<BER-encoded data>' | |
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+------------------------------------------------------------------+ |
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In the case of CMIP, ASN.1 values can be very complex hence it is |
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necessary to identify a mapping from ASN.1 to strings and |
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vice-versa. For this purpose, a mapping such as the one defined in |
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[CMIPRun] can be used. |
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The following examples show how to use the mapping between SNMP/CMIP |
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and URL. Supposing we have an HTTP server (or the proxy) running on |
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host kis.zurich.ibm.com: |
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1. SNMP |
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get the value of sysDescr.0 contained in the SNMP agent running |
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on host bal.zurich.ibm.com: |
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http://kis.zurich.ibm.com/SNMP/GET/sysDescr.0?Host=bal.zurich.ibm. |
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com&Community=public |
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Example 1: SNMP Request |
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Expires May 19, 1997 [Page 3] |
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Internet Draft HTTP-based SNMP and CMIP Network Management Nov. 19, 1996 |
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2. CMIP |
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set the administrativeState attribute to 'enabled' of the managed |
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object instance systemId=(name IBM) contained on the agent whose |
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AE-title is abc: |
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http://kis.zurich.ibm.com/CMIP/SET/abc/systemId=(name+IBM)?administrative |
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State=enabled&timeout=30 |
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Example 2: CMIP Request |
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In the case CGI is used, the HTTP server has to be configured in such |
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a way that it recognises the protocol name and then starts CGI |
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applications whose names correspond to the value of <operation>. For |
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the previous examples, a possible configuration file for an HTTP |
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server is: |
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ScriptAlias /CMIP/ /usr/local/httpd/CMIP-bin/ |
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ScriptAlias /SNMP/ /usr/local/httpd/SNMP-bin/ |
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Figure 2: Sample HTTP configuration for CGI applications |
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where on every -bin directory the CGI applications are contained. For |
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instance, in the Example 1., inside the directory |
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/usr/local/httpd/SNMP-bin/ there is a CGI application called GET. |
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4. SNMP/CMIP requests over HTTP |
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Once the mapping between SNMP/CMIP and URLs is defined, it is now |
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necessary to specify what the format of the information returned by |
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the HTTP protocol is. Supposing the URL shown in the Example 1 is |
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selected, an HTTP client will send the following data to the HTTP |
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server running on kis.zurich.ibm.com: |
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GET SNMP/GET/sysDescr.0?Host=bal.zurich.ibm.com&Community=public HTTP/1.0 |
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[empty line] |
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Figure 3: Data sent by an HTTP client in order to issue |
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the request shown in Example 1 |
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The HTTP response, returned by the HTTP server, is always positive |
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(HHTP wise) unless the requested URL cannot be found or if some other |
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problem arose (for instance authentication problems). In case the HTTP |
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response is positive, it will contain the SNMP response which can be |
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either positive or negative. The HTTP response contains a set of pairs |
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(<identifier>, <value>) separated with carriage return. In case the |
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SNMP response is negative, the last pair is (<empty line>, <error |
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code>) where <error code> contains the error code corresponding to the |
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SNMP request in numeric or string format (for instance "noSuchName" or |
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"2" as defined in the SNMP RFC). Identifiers are object identifiers, |
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usually in symbolic form, whereas values are strings encoded using the |
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encode scheme used by the HTTP protocol. Each line part of the HTTP |
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response is encoded using the URL encoding. This is necessary to avoid |
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that characters like '\n' or '\r', which may be part of the response, |
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interfere with the carriage return used to separate the |
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lines. Multipart MIME encoding can be used as well but it is much more |
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complicated than URL encoding. |
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Expires May 19, 1997 [Page 4] |
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Internet Draft HTTP-based SNMP and CMIP Network Management Nov. 19, 1996 |
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A positive response for the previous requests is the following: |
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HTTP/1.0 200 OK |
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Server: IBM ZRL Proxy Server |
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Date: Fri, 28 Jun 1996 12:30:16 GMT |
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Content-type: text/x-www-form-urlencoded |
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Content-length: 35 |
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sysDescr.0 |
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IBM+RISC+System%2F6000 |
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The proposed solution allows to return both a single response or to |
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return multiple responses encapsulated in a single HTTP response. In |
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the case of SNMP Walk for instance, the response contains multiple |
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pairs, one for each element of the MIB. HTTP responses can contain |
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additional fields, like the value type (for instance 'TimeTicks'), |
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which can be used by the client application (for instance the WWW |
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browser) to display the returned value properly. |
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Similar considerations can be done for CMIP. The only difference with |
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respect to SNMP is that CMIP scoped requests can return multiple CMIP |
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responses where each CMIP response contains multiple attributes |
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relative to a specific object instance. In this case CMIP responses |
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are separated with a (<empty line>, <empty line>). Please note that if |
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the first line of the HTTP response is an <empty line> when the |
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response is negative otherwise it is positive. Due to this there is |
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not ambiguity between (<empty line>, <empty line>) and (<empty line>, |
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<error code>) in case <error code> is empty. |
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5. Conclusion |
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The network management world can significantly benefit from the use of |
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the WWW. This document proposes a way to issue network management |
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requests using the HTTP protocol. Major characteristics of the |
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proposed solutions are: |
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* use of the standard HTTP protocol; |
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* use of symbolic strings which are handled efficiently by common tools |
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such as awk, sed, and perl and (almost) any programming language; |
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* ability to manage SNMP/CMIP resources located across firewalls using |
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the HTTP protocol. |
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This work puts the emphasis on the communication aspect rather the |
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programming aspect. In order to create systems manageable using HTTP, |
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it is necessary to specify the format of the request/response leaving |
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freedom to the developers to select the most appropriate way to issue |
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requests and to handle responses. |
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6. Acknowledgements |
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The author gratefully acknowledges Robert Akolk, Bela Ban, Benjamin |
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Reed and Bert Wijnen for all their comments and suggestions. |
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7. References |
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[CMIP] ISO/IEC, CCITT, "Information Technology-OSI, Common Management |
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Information Protocol (CMIP)-Part 1": Specification ISO/IEC 9596-1, |
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CCITT Recommendation X.711, 1991. |
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Expires May 19, 1997 [Page 5] |
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Internet Draft HTTP-based SNMP and CMIP Network Management Nov. 19, 1996 |
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[CMIPRun] Wade Allen, "An Alternate API for Representing ASN.1 |
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Values", CMIP Run! Magazine, Volume 2, Number 4, 4Q93. |
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[Hazewinkel] H. Hazewinkel, E. van Hengstum and A. Pras, "Definitions |
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of Managed Objects for HTTP", draft-hazewinkel-httpmib-00.txt, |
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University of Twente, April 1996. |
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[HTML] D. Raggett, "HyperText Markup Language Specification Version |
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3.0 (HTML)", Internet Draft, April 1995. |
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[HTTP] T. Berners-Lee, R. Fielding and H. Frystyk, "Hypertext Transfer |
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Protocol HTTP/1.0", RFC 1945, May 1996. |
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[SNMP] J. Case, M. Fedor, M. Schoffstall and C. Davin, "The Simple |
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Network Management Protocol (SNMP)", RFC 1157, May 1990. |
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[URL] T. Berners-Lee, "Uniform Resource Locators (URL)", Internet |
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Draft, March 1994. |
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Expires May 19, 1997 [Page 6] |
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