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Check a Network Response

Three modes are available distinguished by the Address field formats detailed below. As networking is inherently unreliable the setting of an alert may be further conditioned on having met the test criteria on up to 8 consecutive evaluations.

Ping Request / Connection Test

An address which merely identifies a host (sans-protocol) causes either a ping request or a simple socket-level test for a listening process;

{Host}[:{Port}]

Host: The IP address, host name or FQDN of the target. Required.

Port (TCP): Either ICMP (Ping) or the TCP port number to connect on. The default is; ICMP.

An alert may then be set or cleared based on whether the request was answered.

Document Request

An address prefixed with the http:// or https:// protocols attempts retrieval of a document (GET);

http[s]://[{Username}.{Password}@]{Host}[:{Port}][/{Path}][?{Query}]

Username.Password: The credentials required to access a resource protected by basic HTTP authentication. Note that the delimiter is a period rather than the more usual colon. Optional.

Host: The IP address, host name or FQDN of the server that hosts the document. Required.

Port (TCP): The TCP port number to connect on. The defaults are; 80 (HTTP) and 443 (HTTPS).

Path: The location of the resource on the server.

Query: A query string which further identifies the desired resource.

A successful request will return up to the first 32KB of the document. Given a supported text encoding this may then be evaluated for a Literal Fragment, with a Regular Expression or in a Numeric Comparison.

SNMP Query

An address prefixed with snmp:// or snmpv2:// is interpreted as an SNMP device query;

snmp[v2]://[{Community}@]{Host}[:{Port}]/{OID}[/(Enumerate)]

Community: A password which grants read-access to this device. The default is; public

Host: The IP address, host name or FQDN of the device. Required.

Port (UDP): The UDP port number to query on. The default is; 161

OID: The Object Identifier targeted by your query. Essentially this identifies a node in the hierarchy of SNMP values maintained by the device. The default is; 1.3.6.1.2.1.1.1.0 (iso.org.dod.internet.mgmt.mib-2.system.sysDescr.value)

(Enumerate) [/]: Rather than attempting to retrieve a single value from the identified node a trailing forward-slash instructs the query to enumerate all values below the node (with each returned on a separate line). Useful when dealing with tabular data and examining capabilities.

A successful query returns 1 or more lines of text which may then be evaluated for a Literal Fragment, with a Regular Expression or in a Numeric Comparison.

A query may be tested (or the values returned by a given device examined) using the SNMP Query utility (in Options > General).

Determining the OIDs supported by a device can sometimes be a difficult proposition as MIBs are initially released as a dense text document from which the dot-delimited numeric paths must be extracted. We've found the following sites useful in this regard; mibDepot, Circitor, SimpleWeb.

11 August 2016