SNMP

1
SNMP

• Where did it come from ?
• Internet Engineering Task Force
• Network Management Area
• SNMP V1
• MIB definitions
• SNMPV2

2
Syntax

• uses ASN.1 (Abstract Syntax Notation)
• binary encoding
• 02 01 06 is a 1 byte integer, value 6
• Primitive Types
• INTEGER, OCTECT STRING, OBJECT
  IDENTIFIER, NULL
• Constructor Types
• SEQUENCE ltprimitive-typegt ... ie. a
  record
• SEQUENCE OF ltprimitive-typegt ... ie. an
  array

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Syntax

• Defined Data Types
• IpAddress what you expect
• Counter non-negative integer that wraps
• Gauge non-negative integer that latches
• TimeTicks time in hundredths of seconds

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SNMP NAMES
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SNMP

• Management Information Base (MIB)
• "database"of network objects
• Groups
• System, Interfaces, Address Translation, IP,
  ICMP, TCP, UDP, EGP
• "Access" and "Status" attributes
• actual variables are "instances" of OIDs
• 1.3.6.1.2.1.1.1.0 sysDescr
• 1.3.6.1.2.1.2.1.1.10.3 ifInOctets for interface 3
• 1.3.6.1.2.1.4.21.1.7.130.56.0.0
• ipRouteNextHop for network 130.56.0.0

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SNMP

• The SNMP protocol itself
• allows inspection and alteration of MIB variables
• UDP Based
• not acknowledged transactions
• PUT, GET, GET-NEXT operators

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SNMPv1 Protocol continued...
get_request
get_response
port 161
get_next_request
port 161
get_response
Manager
Agent
set_request
port 161
get_response
trap
port 161
port 162
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SNMPv1 Packet Format
UDP Header
PDU Type
Request ID
Error Status
Error Index
Version
Community
name
value
name
...
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SNMP

• SNMP Traps
• unsolicited notification of events
• can include variable list
• ColdStart, WarmStart
• LinkUp, LinkDown
• Authentication Failure
• EGP Neighbour Loss
• Enterprise Specific

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Network Management Software

• SNMP Agents
• provided by all router vendors
• many expanded (enterprise) MIBs
• bridges, wiring concentrators, toasters

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Network Management Software

• Public Domain
• Application Programming Interfaces available from
  CMU and MIT
• include variety of applications

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Network Management Software

• Commercially
• many offerings, UNIX and PC based
• HP OpenView
• SunNet Manager
• Cabletron Spectrum
• MANY others

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Applications
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Receiving MTA
Sending MTA
Open TCP connection on port 25
220 id, ready, time
Hello name
250 id, Hello pleased to meet.
Mail From source_name_at_yahoo.com
250 source_name_at_yahoo.com Sender OK
RCPT To receiver_name_at_hotmail.com
250 receiver_name_at_hotmail.com Recipient OK
DATA
354 Mail goes here, end with a . line
.
.
250 Mail Accepted
QUIT
221 Delivering Mail
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(No Transcript)
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• Example of mail retrieval using POP

POP Mail Server / Local MTA
POP Client
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Network Address Translation (NAT)
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NAT