SNMP Agent

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SNMP Agent
Mi-Jung Choi DPNM Lab. Dept. of Computer
Science and Engineering POSTECH, Pohang
Korea Tel [phone] Email
mjchoi_at_postech.ac.kr
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Contents

• Introduction SNMP agent, SNMP NM architecture
• AgentX
• Architecture
• AgentX Roles
• Advantages Disadvantages
• MIB File
• Back-end Process
• Get, Set operation
• Future work
• References

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Introduction

• SNMP (Simple Network Management Protocol) is
  Internet Network Management Framework which
  includes
• Management architecture
• Structure of management information
• Management protocol
• Related concepts
• IETF (Internet Engineering Task Force) makes SNMP
  standardization
• Protocol Architecture

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SNMP NM Architecture

• The manager resides in NMS (Network Management
  Station) while the agent resides in the managed
  Network Nodes
• The main manager requests the agent to perform
  Set and Get operations on the variables in the
  Management Information Base (MIB)

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AgentX

• Motivation of AgentX
• Need to dynamically extend the management objects
  within a node ? Rise to a variety of extensible
  agents
• The wide development of extensible SNMP agents,
  coupled with the lack of Internet Standards,
  makes it to difficult to field SNMP-manageable
  applications ? Specifying a standard protocol for
  agent extensibility (AgentX) provides the
  technical foundation solving these problems
• AgentX protocol messages appear similar in syntax
  and semantics to the SNMP, but the AgentX is not
  SNMP

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Architecture
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Architecture contd

• A Master agent
• Available on the standard transport address and
• Accepts SNMP protocol message
• A Set of Sub-agents
• Each subagents contains management instruction
• AgentX Protocol
• A Protocol between the Master agent and Subagents
• Permits subagents to connect to the master agent
• The master agent to multiplex received SNMP
  protocol messages amongst the subagents

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AgentX Roles

• Master agent
• Accepts AgentX session establishment requests
  from subagents.
• Accepts registration of MIB regions by subagents.
  
• Sends and accepts SNMP protocol messages on the
  agent's specified transport addresses.
• Sends and receives AgentX protocol messages to
  access management information, based on the
  current registry of MIB regions.
• Subagents
• Initiates AgentX sessions with the master agent.
• Registers MIB regions with the master agent.
• Instantiates managed objects.
• Binds OIDs within its registered MIB regions to
  actual variables.
• Performs management operations on variables.

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Advantages Disadvantage

• Advantages
• A general architectural division of labor between
  master agent and subagent The master agent is
  MIB ignorant and SNMP omniscient, while the
  subagent is SNMP ignorant and MIB omniscient (for
  the MIB variables it instantiates). That is,
  master agents, exclusively, are concerned with
  SNMP protocol operations and the translations to
  and from AgentX protocol operations needed to
  them out subagents are exclusively concerned
  with management instrumentation and neither
  should intrude on the other's territory.
• A standard protocol and "rules of engagement" to
  enable interoperability between management
  instrumentation and extensible agents. 3)
• Disadvantage
• Performance problem It is likely that the
  master agent and all subagents will reside on the
  same host, and in such cases AgentX is more a
  form of inter-process communication than a
  traditional communications protocol

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MIB-II File

• MIB-II Group
• System Information, Interface, Address
  Translation, IP, ICMP, TCP, UDP, EGP, SNMP
• Not support file system pHILE
• Read MIB Pares MIB ? Use Buffer

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Back-end Process

• Registration
• session agentx_open( 10, oid, "session 1"
  )
• reg agentx_register( session, 0, 0, 127, 7,
• agentx_newoid( 7, 1, 3, 6, 1, 2, 1, 4 ) )
• map agentx_mapget ( reg, 0, NULL, ip_get,
  ip_getn )
• agentx_mapset( map, ip_Forwarding, ip_Default,
  NULL, NULL)

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Backend Process Contd

• MIB definition
• ipForwarding OBJECT-TYPE
• SYNTAX INTEGER
• forwarding(1), --
  acting as a gateway
• not-forwarding(2) --
  NOT acting as a gateway
• ACCESS read-write
• STATUS mandatory
• Backend Process (Get operation)
• s s_socket(AF_INET, SOCK_STREAM, 0)
• varbind-gttype agentx_Integer
• s_ioctl(s, SIOCGIPFORWARDING,
  varbind-gtdata.int_data)
• s_close(s)

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Backend Process Contd

• Backend Process (Set operation)
• s s_socket(AF_INET, SOCK_STREAM, 0)
• varbind-gttype agentx_Integer
• s_ioctl(s, SIOCSIPFORWARDING,
  varbind-gtdata.int_data)
• s_close(s)
• Backend Process (Get table index)
• s_sioctl(s, SIOCFIPROUTETABLE, arg)
• for (i0 iltarg.leni)
• s_ioclt(s, SIOCGIPROUTEIFINDEX , routesi)
• varbind-gttype agentx_Integer
• varbind-gtdata_int_data routesi.ir_ifindex
• .

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Future Work

• RMON agent
• Insert delete table entry
• trap operation
• Define implement private MIB

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References

• William Stallings, SNMP, SNMPv2, SNMPv3 and RMON1
  and 2, Third eddition, Addison-Wesely, ISDN
  0-201-48534-6, 1999
• M. Daniele, B. Winnen, Agent Extensibility
  (AgentX) protocol, RFC 2257, January 1998
• AgentX at Carnegie Mellon Network Development
  http//www.net.cmu.edu/groups/netdev/agentx/
• IETF Agentx Working Group http//www.scguild.com/a
  gentx/
• pSOS manual TCP/TP for OpEN Users Guide