Remote Network Monitoring (RMON)*

*Mani Subramanian “Network Management: Principles and practice”, Addison-Wesley, 2000.

Outline

Basic Conceptso RMON Goalso Control of Remote Monitorso Multiple Managerso Table Management

Statistics group History group Host and hostTopN groups Matrix group Alarm group Filter and packet Capture group

Basic Concepts

Extends the SNMP functionality without changing the protocol

Allows the monitoring of remote networks (inter-network management)

MAC-layer (layer 2 in OSI) monitoring

Defines a Remote MONitoring (RMON) MIB that supplements MIB-IIo with MIB-II, the manager can obtain information on

individual devices onlyo with RMON MIB, the manager can obtain information

on the LAN as a whole

Basic Concepts

called network monitors, analyzers or probes A monitor generally can produce summary

information on o error statistics, e.g., counts # of collisions on a LANo Performance statistics: #packets delivered per

second, packet size distribution, etc.

A monitor also can store packets for later analysis

A Monitor may also filter data to limit the # packets counted or captured o filter based on packet type or characteristics (e.g.,

packets with certain source address, erroneous packets)

Basic Concepts

A Monitor is required per subnetwork o A monitor could either be a standalone device whose

only job is monitoring and traffic analysis o or it could also be a device with other functionalities

(e.g., router, server)

A monitor usually communicates with one (or more) central MS

RMON essentially is a definition of a MIBo Standard monitoring functions and interfaces for

communication between SNMP consoles and remote monitors

RMON Goals Monitoring subnetwork-wide behavior while

reducing the burden on agents and managerso Monitors and analyzes locally and relays data

Continuous off-line monitoring in the presence of failureso RMON should collect fault, performance, and configuration

information continuously even when it is not being polled save communication cost

o This information may be retrieved later by a manager

Proactive monitoring o Continuously runs diagnostics and store network

performance even in the absence of failureso Upon a failure, notify the manager and provide him with

useful info to be able to diagnose the fault

RMON Goals

Provide value-added datao Perform analysis on collected data, thus

relieving the MS from this responsibility

Support multiple managerso Multiple managers improves reliability, provides

diversity in network management, etc.o A monitor should be configured to deal with

more than a manager simultaneously

Network with RMONs

BridgeBridge

RouterRouter

RouterRouter

RouterRouter

RouterRouter

FDDI backbone

Token Ring LAN

Router withRMON probe

Management consolewith RMON probe

Central Site

Local management console withRMON probe

PC with RMON probe

PC withRMON probe

Ethernet

Ethernet

Ethernet

Control of RMON- Configuration

RMON is configured for data collection:o RMON MIB contains a

number of functional groups

Each group may contain one or more “control tables” and one or more “data tables”

o Control tables (read-write) contain parameters describing data in data tables (read-only)

A NMS sets appropriate control parameters to configure RMON to collect the desired data: The parameters are set by

adding a new row to the “control table” or by modifying an existing row

As information is collected, data is stored in rows of the corresponding “data table”

Control of RMON- Configuration Functions performed by a

monitor are defined and implemented in terms of table rowso Control table may

contain objects that specify the “source of data” to be collected, the “type of data”, the “collection timing”, etc.

o Associated with a single control row are one ore more rows in one or more data tables

To modify a particular data collection function:

o it is necessary first to invalidate the control rowo this causes the deletion of that row and the deletion of all associated rows in data tableso NMS can create a new control row with the modified parameters

NOTE: when a row of a control table is deleted, associated rows in data tables are also deleted.

Multiple Managers RMON probe may be subject to management

from multiple MSs

Potential conflict and unwanted resultso Simultaneous requests for resources could exceed the

capability of the monitoro Monitor resources could be captured by a MS for a

long time, preventing other MSs from accessing desired information

o Resources could be assigned to a MS that crashes without releasing resources

Avoidance and resolution features are required

o Ownership label: identifies the owner of a particular row of the control table and associated function

Multiple Managers RMON suggests that ownership label contains one or

more of:o IP address, management station name, network manager’s

name, location or phone number

The ownership label can be used in the following wayso A MS may recognize resources it owns and no longer needso A network operator can identify the MS that owns a

particular resource and negotiate its releaseo A network operator may have the authority unilaterally to

free resourceso A MS after experiencing failure or re-initialization can

recognize resources it had reserved in the past and free those it no longer needs

NOTE: o A row in a control table should only then be altered by its

owner and read by other MSs.

Multiple Managers

Resource sharing to improve efficiencyo If a certain management function has been defined by

some MS, another MS can share its usage by observing the associated “read-only” data rows (see EntryStatus definition)

o However, the MS that owns this control row may modify or delete the row at any time (and hence the associated data rows)

Monitor’s default functionso These are monitoring functions owned by the monitor

itselfo By convention, such ownership labels start with

“monitor”o A MS can make use of such resources in a read-only

fashion

Indicates the status of the row

Indicates the owner of a row in control table

Table Management The RMON specification includes a set of textual

conventions and procedural rules for row addition and deletion

Textual conventions: 2 new data types

OwnerString ::= DisplayStringEntryStatus ::= INTEGER {

valid (1),createRequest (2),underCreation (3),invalid (4)

}State Enume

-ration Description

valid 1 Row exists and is active. It is fully configured and perational createRequest 2 Create a new row by creating this object underCreation 3 Row is not fully active invalid 4 Delete the row by disassociating the mapping of this entry

Control Tablerm1ControlTable OBJECT-TYPE SYNTAX SEQUENCE OF RM1ControlEntry Access not-accessible STATUS mandatory DESCRIPTION "A control Table." ::= {ex1 1}

rm1ControlEntry OBJECT-TYPE SYNTAX RM1ControlEntry Access not-accessible STATUS mandatory DESCRIPTION "defines a parameter that controls a set of data table entries." INDEX {rm1ControlIndex} ::= {rm1ControlTable 1}

rm1ControlIndex OBJECT-TYPE SYNTAX INTEGER Access read-only STATUS mandatory DESCRIPTION "the value of this object uniquely identifies this rm1Control Entry" ::= {rm1ControlEntry 1}

RM1ControlEntry ::= SEQUENCE { rm1ControlIndex INTEGER rm1ControlParameter Counter rm1ControlOwner OwnerString rm1ControlStatus RowStatus }

rm1ControlParameter OBJECT-TYPE SYNTAX INTEGER Access read-write STATUS mandatory DESCRIPTION "the value of this object characterizes data rows associated with this entry" ::= {rm1ControlEntry 2}

rm1ControlOwner OBJECT-TYPE SYNTAX OwnerString Access read-write STATUS mandatory DESCRIPTION "the entity that configured this entry" ::= {rm1ControlEntry 3}

rm1ControlStatus OBJECT-TYPE SYNTAX EntryStatus Access read-write STATUS mandatory DESCRIPTION "the status of this rm1Control entry” ::= {rm1ControlEntry 4}

Data Table

rm1DataTable OBJECT-TYPE SYNTAX SEQUENCE OF RM1DataEntry Access not-accessible STATUS mandatory DESCRIPTION "A data Table." ::= {ex1 2}

rm1DataEntry OBJECT-TYPE SYNTAX RM1DataEntry Access not-accessible STATUS mandatory DESCRIPTION "A single data table entry." INDEX {rm1DataControlIndex, rm1DataIndex} ::= {rm1DataTable 1}

RM1DataEntry ::= SEQUENCE { rm1DataControlIndex INTEGER rm1DataIndex INTEGER rm1DataValue Counter}

rm1DataControlIndex OBJECT-TYPE SYNTAX INTEGER Access read-only STATUS mandatory DESCRIPTION "the control set of which this entry is a part. The control set identified by a value of this index in the same control set identified by the same value of rm1ControlIndex " ::= {rm1DataEntry 1}

rm1DataIndex OBJECT-TYPE SYNTAX INTEGER Access read-only STATUS mandatory DESCRIPTION "An index that uniquely identifies a particular entry among all data entries associated with the same rm1ControlEntry" ::= {rm1DataEntry 2}

rm1DataValue OBJECT-TYPE SYNTAX Counter Access read-only STATUS mandatory DESCRIPTION "the value reported by this entry" ::= {rm1DataEntry 3}

Control and Data Table- Examplerm1ControlTable

1 5 monitor valid (1)

2 26 manager alpha valid (1)

3 19 manager beta valid (1)

1 46

1 96

2 85

3 77

4 27

5 92

1 86

2 26

rmlControlIndex rmlControlParameter rmlControlOwner rmlControlStatus

rm1DataTable

rmlDataControlIndex rmlDataIndex rmlDataValue

1

2

2

2

2

2

3

3

Row Addition and deletion A MS uses SNMP messages to add

a row into an RMON tableo SetRequest-PDU message will

contain a list of object identifiers for all columns in the table

When a monitor receives a request

o it must check whether there are any restrictions defined in the RMON MIB (object is not currently supported by the MIB)

o or any implementation specific restrictions (e.g., lack of resources)

If row addition is not possibleo GetResponse-PDU with

badValue error is returned

Multiple managers attempt for row addition

o multiple requests to create a row with same parameters, including index parameters conflict

o Conflict arbitration is required

o Only the first request is awarded

Row Deletiono is achieved by (the owner)

setting the status object for that row to “invalid”

Row Modificationo is achieved by first

invalidating the row and then adding the row with new object instance values

RMON MIBrmon (mib-2 16)

statistics (1)

history (2)

alarm (3)

host (4)

hostTopN (5)

matrix (6)

filter (7)

capture (8)

event (9)

tokenRing (10)

Each group is used to store data and statistics derived from data collected by the monitor

A monitor may have more than one physical interface and hence may be connected to more than one sub-network

10 groups

agenta

agentb

RMONprobe

agentc

agente

agentd

Interface 1

Interface 2

SubnetworkX

SubnetworkY

Statistics Group

Basic statistics for each monitored subnetwork

A “single” table with one entry for each interface

Variety of counts for each subnetwork, such as: bytes, packets, errors, frame sizes, etc.

Provides useful information about the load on a subnetwork and its health (counts collisions, etc..)

agenta

agentb

RMONprobe

agentc

agente

agentd

Interface 1

Interface 2

SubnetworkX

SubnetworkY

History Group

Sampling function for one or more of the interfaces of the monitor historyControlTable:

specifies the interface and details of the sampling function

etherHistoryTable: records data

historyControlTable defines a set of samples at a particular sampling interval for a particular interface

historyControlIndex identifies a row in the control table

historyControlDataSource identifies interface or subnetwork that is source of data

historyControlBucketsRequestedrequested # sampling intervals over which data is saved in the data table (default value = 50)

historyControlBucketsGranted actual # sampling intervals over which data will be saved

historyControlInterval interval in seconds over which data is sampled (default value = 1800 seconds (30 minutes))

History GrouphistoryControl-

IndexhistoryControl-

DataSourcehistoryControl-BucketsGranted

historyControl-Interval

1

2

K

D1

D2

DK BK

B2

B1 I1

I2

IK

histroyControlTable

1

1

1

1

2

2

2

x+1

x+2

x+3

x+B1

y+1

y+2

y+B2

etherHistoryTable

etherHistoryIndex etherHistorySampleIndex

History Group etherHistoryTable

o etherHistoryIndex: the history of which this entry is part (index)

o etherHistorySampleIndex: identifies the particular sample among all samples associated with the same row in control table

Table contains also some useful counterso etherStatsOctets: # of

received octets of datao etherStatsPkts: # of

received packets, etc…

Subnetwork utilization:o : medium data rate (bps)o T: sampling interval (seconds)o Pkts = [ etherStatsPkts ]2 -

[ etherStatsPkts ]1

o Octets = [etherStatsOctets]2 - [ etherStatsOctets ]1

o = utilization

T

(1) (2)

Pkts(96+64) + (Octets8) = T

NOTE: 64-bit preamble, and 96-bit IFG

History Group For a given subnetwork,

historyControlDataSource, more than one sampling process is allowed at different sampling period historyControlInterval

o Sampling over short period (e.g. 30s) enables the monitor to detect sudden changes in traffic pattern

o Sampling over long periods (e.g., 30 minutes) enables a monitor to observe the steady state behavior of certain interface

After each sampling interval, the monitor adds a new row to the etherHistoryTable with the same etherHistoryIndex When the # rows of a history becomes equal to

historyControlBucketsGranted, as each new row is added, the oldest row associated with this history is deleted. “circular buffer”

History Group

historyControl-Index

historyControl-DataSource

historyControl-BucketsGranted

historyControl-Interval

1 D1 B1 I1

histroyControlTable

1

1

x+1

x+2

2 y+1

etherHistoryTableetherHistorySampleIndexetherHistoryIndex

1 x+3 A new sample added

2 D2 B2 I2

A new interface or subnetwork

2

2

y+2

y+B2

History Group

historyControl-Index

historyControl-DataSource

historyControl-BucketsGranted

historyControl-Interval

1 D1 B1 I1

histroyControlTable

1

1

x+1

x+2

2 y+2

etherHistoryTableetherHistorySampleIndexetherHistoryIndex

1 x+3 A new sample added

2 D2 B2 I2

A new interface or subnetwork

2

2

y+3

y+B2+1

Oldest entry (sample) is deleted

host and hostTopN Groups host Group

o Gather statistics about specific hosts on the LANo hostInPkts, hostOutPkts, etc..

o By observing s-d MAC addresses in monitored packets, a monitor can discover new attached hosts on the LAN

hostTopN Groupo To maintain statistics about the set of hosts on one

subnetwork that top a list based on some parametero List of the 10 hosts that transmitted the most data

during a particular dayo List of nodes ordered according to errors they’ve sent

in the last hour

Matrix Group Record information about

traffic between pairs of hosts on a subnetwork

o error and utilization, e.g. traffic amount, number of errors

Information is stored in the form of a matrix so the operator can

retrieve information for any pair of network addresses, e.g., to find which devices are making the most use of a server

matrixControlTable:o matrixControlIndex integer

uniquely identifies a row.o matrixControlDataSourceInterface

that is source of traffico matrixControlTableSize # of rows

in data table (matrixSDTable) associated with this row

matrixSDTable: o store statistics on traffic from a

source to multiple destinationso matrixSDSourceAddress: MAC

address of sourceo matrixSDDestAddress: MAC

address of destinationo matrixSDPckts: # packets

transmitted from s- to d-o matrixSDOctets: # octets in

packets transmitted from s- to d-

alarm Group Measuring network performance consists of identifying

abnormal conditions by the monitor and issuing alarms accordingly:

o e.g., if there are more than 200 CRC errors (the threshold) in any 5-minute period (the sampling interval), an alarm is generated and sent to the central console.

Alarm group contains a single table alarmTable, each entry:o a variable to be monitored (alarmVariable)

o INTEGER, counter, gauge, TimeTickso A sampling interval (alarmInterval)o most recent sampled value (alarmValue)o Threshold parameters

o alarmRisingThreshold, and alarmFallingThresholdo alarmStartupAlarm

o alarm is generated when a row becomes active and 1st sampled value risingThreshold, or fallingThreshold or both

alarm GroupMode of operation:

Rising threshold (RT) and Falling threshold (FT) are defined RT is crossed when current sampled value is greater than

RT and value of last sampling interval was less than threshold

FT is crossed when current sampled value is less than FT and value of last sampling interval was greater than threshold

absoluteValue and deltaValue (difference of 2 successive intervals). Counter use deltaValue

Fluctuations not counted! Avoid generating excessive alarms

Time

Sampled Object value

Rising threshold

Fallingthreshold

filter Group Observing only “selected

packets” on a particular interface Data filter

o Screen observed packets based on a bit pattern that a portion of the packet matches (or fails to match)

Status filtero Screen observed packets

based on their status (e.g., valid, CRC errors, etc.)

Example: screen those packets on some interface with certain source MAC address!

The monitor may capture packets that pass the filter or simply record statistics based on such packets

Both filters can be combined to form a complex test to be applied to incoming packets

o filter test example: we wish to accept all Ethernet packets with destination address 0xA5 and that do not have a source address of 0xBB!

capture Group

event Group Supports definition of

events (problems, symptoms of problems)

o An event is triggered by a condition located elsewhere in the MIB

o E.g., monitoring a variable that crossed a rising threshold would cause an event to be generated

Controls the generation and notification of events

An event may cause an SNMP trap message to be issued by the monitor

eventTable: eventDescritpion: textual

description of the event eventType: none(1), log(2), snmp-

trap (3) log-and-trap(4) log: an entry is added to the

logTable for this event snmp-trap: an SNMP trap is

sent to a MS eventCommunity: identifies the

communities of MSs to receive the SNMP trap, etc.

logTable: logTime: value of sysUpTime

when this log entry was created logDescription: description of the

event that activated this entry (implementation-dependent)

logEventIndex: the event that generated this log entry

RMON2

FDDIBackbone Network

Remote Token Ring LANNMS

Router Bridge

Token Ring

Probe

Ethernet

Probe

Local LAN

Router with

RMON

Router

Remote FDDI LAN

FDDI Probe

Enable probes to look beyond LAN segments Analyze traffic passing through the router to determine the

ultimate source and destination Monitor application level traffic (e-mails, file transfer,

WWW, etc.)