1. SNMP (Simple Network Management Protocol) Jon Sevy Geometric and Intelligent Computing Laboratory Department of Mathematics and Computer Science Drexel University http://gicl.mcs.drexel.edu

2. SNMP Overview Define mechanism for remote management of network devices (routers, bridges, etc.) Fundamental principle: all device management done by simple variable value manipulation Approach: –standard means for specifying quantities recognized by devices –protocol for requesting, returning, notifying of changes of values

3. SNMP Message Protocol Messages use UDP, ports 161 (requests/responses) and 162 (notifications) Message types: –GetRequest: request values of variables from device –GetNextRequest: request value of variable following the one supplied –GetResponse: return values –SetRequest: instruct device to set values of variables –Trap: from device - notify monitor / manager of value change

4. SNMP Communities Define “communities” specifying access to specific variable sets (read-write, read only, none) Supply community name as “password” in each message –unencrypted in version of SNMP still widely used!!

5. SNMP Message Encoding Encode message as byte stream using ASN.1 BER (Abstract Syntax Notation 1 Basic Encoding Rules) Quantites encoded as Type,Length,Value triples Types –Subset of basic ASN.1 types used in SNMP: integer, octet string, object identifier (“variable name”), sequence –SNMP-defined types: gauge, counter, IP address, etc. Values –weirdly encoded!! (see ASN.1 specs)

6. SNMP SMI (Structure of Management Information) Variables recognized by device supplied in MIB (Management Information Base) –text file giving variables and data structures defined using ASN.1 –standard variable sets often provided as RFC’s –device-specific sets provided by vendors Management stations parse MIB’s to determine variables available for management –obtain both data structure and management information

7. Example portion of MIB (from RFC 1213) -- the Interfaces group -- Implementation of the Interfaces group is mandatory for -- all systems. ifNumber OBJECT-TYPE SYNTAX INTEGER ACCESS read-only STATUS mandatory DESCRIPTION "The number of network interfaces (regardless of their current state) present on this system." ::= { interfaces 1 }

8. ASN.1 Object Identifiers Variables identified by globally unique strings of digits –ex: 1.3.6.1.4.1.3.5.1.1 –name space is hierarchical; tree on next slide in above, 1 stands for iso, 3 stands for org, 6 stands for dod, 1 stands for internet, 4 stands for private, etc. Variable names are aliases for digit strings (within MIB) –From previous page: ifNumber ::= { interfaces 1 } –interfaces was previously defined in MIB as 1.3.6.1.2.1.2, so ifNumber = 1.3.6.1.2.1.2.1

9. Partial ASN.1 Object Identifier Tree (from: ASN.1 Complete, J. Larmouth, Open Systems Solutions, 1999)

10. Application: GICL SNMP Monitor Java-based SNMP application –Query devices for available MIB variables –Set desired variable values Current status –retrieve and display all values from device –automatically build data structures to hold retrieved values Future work –incorporate MIB information via MIB parser –auto-generate GUI display –implement device discovery

11. References Internet Standards 15, 16 and 17 ASN.1 Complete, J. Larmouth, Open Systems Solutions, 1999 (available online) SNMP : a guide to network management, S. Feit, McGraw-Hill, 1995