Chapter 7. How to Graph Your Network

Table of Contents
Creating a Device
Creating the Graphs

At this point, you probably realize that graphing is Cacti's greatest strength. Cacti has many powerful features that provide complex graphing and data acquisition, some which have a slight learning curve. Do not let that stop you however, because graphing your network is incredibly simple.

The next two sections will outline the two basic steps which are typically required to create graphs for most devices.

Creating a Device

The first step to creating graphs for your network is adding a device for each network device that you want to create graphs for. A device specifies important details such as the network hostname, SNMP parameters, and host type.

To manage devices within Cacti, click on the Devices menu item. Clicking Add will bring up a new device form. The first two fields, Description and Hostname are the only two fields that require your input beyond the defaults. If your host type is defined under the host template dropdown, be sure to select it here. You can always choose "Generic SNMP-enabled Host" if you are just graphing traffic or "None" if you are unsure. It is important to remember that the host template you choose will not lock you into any particular configuration, it will just provide more intelligent defaults for that type of host.

Figure 7-1. Adding a New Device

The field definitions are as follows

Table 7-1. Device Field Definitions

DescriptionThis description will show up in the first column of the device list. You may refer to it e.g. in graph titles
HostnameEither an IP address or a hostname. The hostname will be resolved using the standard host resolving mechanisms, e.g. Dynamic Name Services (DNS)
Host TemplateA Host Template is a container for a list of graph templates that will be related to this host.
NotesNew with cacti 0.8.7. Add notes to a host to add arbitrary text.
Disable HostExclude this host from being polled. This is of particular value, if a device is no longer available, but should be kept e.g. as a reference.
Availability/Reachability Options 
Downed Device Detection

NONE: Deactivate downed host detection

PING and SNMP: perform both tests

SNMP: verify SNMP check on OID .1 and .1.3

ICMP: perform a ping test, see below

Ping Method

Available only for "PING and SNMP" or "PING"

ICMP: perform ICMP tests. Requires permissions

UDP: perform a UDP test

TCP: perform a TCP test

Ping Port

Available only for UDP/TCP PING test types.

Please define the port to be tested here. Make sure, that no firewall intercepts the tests

Ping Timeout ValueAfter this time, the test fails. Measured in units of milliseconds
Ping Retry CountThe number of times Cacti will attempt to ping a host before failing.
SNMP Options 
SNMP Version

Version 1: Use SNMP Version 1. Be aware, that 64bit counters are not supported in this SNMP version

Version 2: Referred to as SNMP V2c in most SNMP documentations

Version 3: SNMP V3, supporting authentication and encryption

SNMP CommunitySNMP read community for this device.
SNMP PortEnter the UDP port number to use for SNMP (default is 161).
SNMP TimeoutThe maximum number of milliseconds Cacti will wait for an SNMP response (does not work with php-snmp support).
Maximum OID's Per Get Request

This is a performance feature. Specifies the number of OID's that can be obtained in a single SNMP Get request.

NOTE: This feature only works when using Spine

NOTE: Some devices do not support values > 1

Security Options for SNMP V3 
SNMP UsernameThe username of an SNMP V3 createUser statement or equivalent
SNMP PasswordThe authpassphrase of an SNMP V3 createUser statement or equivalent
SNMP Auth ProtocolThe authentication type of an SNMP V3 createUser statement or equivalent. Select either MD5 or SHA. This entry defaults to MD5.
SNMP Privacy PassphraseThe privacy passphrase of an SNMP V3 createUser statement or equivalent.
SNMP Privacy ProtocolThe privacy protocol of an SNMP V3 createUser statement or equivalent. Select either DES or AES. This entry defaults to DES.
SNMP ContextWhen using the View-Based Access Control Model (VACM), it is possible to specify an SNMP Context when mapping a community name to a security name with a com2sec directive, with the group directive and the access directive. This allows for defining special access models. If using such a parameter with your target's SNMP configuration, specify the context name to be used to access that target here.

After saving your new device, you should be redirected back to the same edit form with some additional information. If you configured SNMP for this host by providing a valid community string, you should see various statistics listed at the top of the page. If you see "SNMP error" instead, this indicates an SNMP problem between Cacti and your device.

Towards the bottom of the page there will be two addition boxes, Associated Data Queries, and Associated Graph Templates. If you selected a host template on the previous page, there will probably be a few items in each box. If there is nothing listed in either box, you will need to associate at least one data query or graph template with your new device or you will not be able to create graphs in the next step. If no available graph template or data query applies to your device, you can check the Cacti templates repository or create your own if nothing currently exists.

A Word About SNMP

The SNMP version that you choose can have a great effect on how SNMP works for you in Cacti. Version 1 should be used for everything unless you have reason to choose otherwise. If you plan on utilizing (and your device supports) high-speed (64-bit) counters, you must select version 2. Starting with Cacti 0.8.7, version 3 is fully implemented.

The way in which Cacti retrieves SNMP information from a host has an effect on which SNMP-related options are supported. Currently there are three types of SNMP retrieval methods in Cacti and are outlined below.

Table 7-2. SNMP Retrieval Types

TypeDescriptionSupported OptionsPlaces Used
External SNMPCalls the net-snmp snmpwalk and snmpget binaries that are installed on your system.All SNMP optionsWeb interface and PHP poller (poller.php)
Internal SNMP (php-snmp)Uses PHP's SNMP functions which are linked against net-snmp or ucd-snmp at compile time.Version 1 Only (Community and Port)Web interface and PHP poller (poller.php)
Spine SNMPLinks directly against net-snmp or ucd-snmp and calls the API directly.All SNMP optionsC-Based Poller (Spine)

SNMP V3 Options Explained

SNMP supports authentication and encryption features when using SNMP protocol version 3 known as View-Based Access Control Model (VACM). This requires, that the target device in question supports and is configured for SNMP V3 use. In general, configuration of V3 options is target type dependant. The following is cited from man snmpd.conf concerning user definitions

[   SNMPv3 Users
       createUser [-e ENGINEID] username (MD5|SHA) authpassphrase [DES|AES] [privpassphrase]

              MD5 and SHA are the authentication types to use.  DES and AES are the privacy
              protocols  to  use. If  the  privacy  passphrase  is not specified, it is assumed
              to be the same as the authentication passphrase.  Note that the users created will
              be useless unless they are also added  to  the  VACM access control tables
              described above.

              SHA  authentication  and DES/AES privacy require OpenSSL to be installed and the
              agent to be built with OpenSSL support.  MD5 authentication may be used without

              Warning: the minimum pass phrase length is 8 characters.]

VACM directives are explained from man snmpd.conf as follows

[   VACM Configuration
       The full flexibility of the VACM is available using four configuration directives -
       com2sec, group,  view and access.  These provide direct configuration of the underlying
       VACM tables.

              map  an  SNMPv1 or SNMPv2c community string to a security name - either from a
              particular range of source addresses, or globally ("default").  A restricted
              source can either be a specific  hostname (or  address),  or  a  subnet -
              represented as IP/MASK (e.g., or IP/BITS
              (e.g., or the IPv6 equivalents.

              The same community string can be specified in several separate directives
              (presumably with different  source  tokens), and the first source/community
              combination that matches the incoming request will be selected.  Various
              source/community combinations can also map to the same security name.

              If a CONTEXT is specified (using -Cn), the community string will be mapped
              to a security  name  in the named SNMPv3 context. Otherwise the default
              context ("") will be used.

       group GROUP {v1|v2c|usm} SECNAME
              maps  a  security name (in the specified security model) into a named group.
              Several group directives can specify the same group name, allowing a single
              access setting to apply to several  users and/or community strings.

              Note  that  groups must be set up for the two community-based models separately -
              a single com2sec (or equivalent) directive will typically be accompanied by two
              group directives.

       view VNAME TYPE OID [MASK]
              defines a named "view" - a subset of the overall OID tree. This is most commonly
              a single subtree, but  several view directives can be given with the same view
              name, to build up a more complex collection of OIDs.  TYPE is either included
              or excluded, which can again define a more complex view (e.g by excluding certain
              sensitive objects from an otherwise accessible subtree).

              MASK is a list of hex octets (separated by "." or ":")
              with the set bits indicating which subidentifiers in the view OID to match against.
              This can be used to define a view covering a particular row  (or  rows) in a table.
              If not specified, this defaults to matching the OID exactly (all bits set), thus
              defining a simple OID subtree.

       access GROUP CONTEXT {any|v1|v2c|usm} LEVEL PREFX READ WRITE NOTIFY
              maps from a group of users/communities (with a particular security model
              and  minimum  security level, and in a specific context) to one of three views,
              depending on the request being processed.

              LEVEL is one of noauth, auth, or priv.  PREFX specifies how CONTEXT should be
              matched against  the context  of  the  incoming  request, either exact or prefix.
              READ, WRITE and NOTIFY specifies the view to be used for GET*, SET and
              TRAP/INFORM requests (althought the NOTIFY view is not currently used).  For
              v1 or v2c access, LEVEL will need to be noauth.]

As an example, following definitions in the snmpd configuration create a set of definitions for use with SNMP V3

# sample configuration for SNMP V3

# create an SNMP V3 user with an authpassphrase and a privacy passphrase
##         username   authProto  authpassphrase  privProto  privpassphrase
##         --------   ---------  --------------  ---------  --------------
createUser gandalf    MD5        myauthpass      DES        myprivpass

# Second, map the security name into a group name:
##    groupName    securityModel  securityName
##    ---------    -------------  ------------
group groupv3      usm            gandalf

# Third, create a view for us to let the group have rights to:
##          incl/excl  subtree   mask
##          ---------  -------   ----
view    all included   .iso      80

# Fourth, create the access for that group without context
##                context sec.model sec.level prefix read   write  notif
##                ------- --------- --------- ------ ----   -----  -----
access groupv3    ""      any       auth      exact  all    all    all

When adding this stuff to your snmp configuration, please remember to restart the agent. Verify this setting using

shell>snmpwalk -v 3 -a MD5 -A myauthpass -x DES \
-X myprivpass -u gandalf -l authpriv localhost interface
IF-MIB::ifNumber.0 = INTEGER: 3
IF-MIB::ifIndex.1 = INTEGER: 1
IF-MIB::ifIndex.2 = INTEGER: 2
IF-MIB::ifIndex.3 = INTEGER: 3
IF-MIB::ifDescr.1 = STRING: lo
IF-MIB::ifDescr.2 = STRING: irda0
IF-MIB::ifDescr.3 = STRING: eth0
IF-MIB::ifType.1 = INTEGER: softwareLoopback(24)
IF-MIB::ifType.2 = INTEGER: other(1)
IF-MIB::ifType.3 = INTEGER: ethernetCsmacd(6)