SNMP (Simple Network Management Protocol)

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