SNMP in RipEX

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2. SNMP in RipEX

RipEX SNMP protocols can be used to:

  • Read configuration parameters,

  • Read operation statistics (interfaces, …), and

  • Send traps/informs when set thresholds for monitored values are exceeded (TxLost [%], UCC, Temp, PWR, …)

For detailed description of individual values refer to section RipEX MIB below.

RipEX utilises SNMP versions SNMPv1, SNMPv2c (using a configurable community string for authentication, which is by default “public“) and SNMPv3 (using Security User name, Security levels, Authentication and Encryption mechanisms). SNMP uses UDP protocol for communication; delivery checks are implemented from version 2 onwards.

[Note]Note

The RipEX MIB module complies with Severity level 3 validation.

By default RipEX uses UDP port 161 (SNMP) for queries. The manager, which sends the query, dynamically chooses the source port. The use of destination port 161 is fixed. RipEX replies from port 161 to the port dynamically selected by the manager.

RipEX launches SNMP agent automatically on start-up if enabled. RipEX also sends alarm states (traps/informs) to the manager via the port 162 (SNMP TRAP/INFORM). Users can change this port number in RipEX for each destination (up to three). The notifications’ behaviour can be influenced (see Alarm management settings, RipEX manual, Adv. config.).

When using SNMP over radio channel we recommend setting RipEX to the Router mode. From the point of radio network, SNMP is typically a standalone application sharing the radio channel with others. Thus it causes collisions, which are automatically resolved by the radio channel protocol in the Flexible Router mode. The radio channel uses no protocol in the Bridge mode, meaning two competing applications can only be run at a great risk of collisions and with the knowledge that packets from both applications may be irretrievably lost.

[Note]Note

Since the firmware 1.6.x, Base Driven Protocol (BDP) has been introduced in the Router mode. SNMP can be, of course, used together with BDP. BDP’s mechanism ensures there is not a single collision on the radio channel.

2.1. Limitations

SNMP is primarily designed for Ethernet networks, where generally, bandwidth capacity is not an issue. By contrast, radio bandwidth capacity is very limited and RipEX mostly works over the radio channel. For this reason, special care is recommended while configuring NMS. If badly configured, NMS can take a significant portion of the network capacity or can even overload the network completely.

2.1.1. Bandwidth Consumption

  • SNMPv2c
    It is important to realise that the average size of a single request and response to a specific OID is approximately 184 Bytes each. The entire MIB for a single RipEX with one neighbouring RipEX is approximately 48 kilobytes. Based on the limitations and the MIB size, we recommend to query only carefully selected OIDs over the radio channel and not all possible data. Set SNMP query time intervals in your NMS as long as possible. The shortest recommended interval ranges from several minutes to tens of minutes.

  • SNMPv3
    With SNMPv3 it is more complicated to define bandwidth consumption because several security levels can be configured (NoAuthNoPriv, AuthNoPriv and AuthPriv). Each level requires different approach and number of packets. For each SNMP GET Request packet, SNMP Report is returned by RipEX (to get the current and unique EngineID, Engine Boots and Engine Time). The following steps are different upon the Security level configuration. For each level, there is an SNMP GET Request and SNMP Response.

  • NoAuthNoPriv:
    Both messages are sent in plain text. No authentication and no Encryption.

  • AuthNoPriv:
    The messages are authenticated, the packet size increases.

  • AuthPriv:
    The messages are authenticated and encrypted, the packet size is the highest.

To obtain any SNMP value using v3 consumes approximately two times more bandwidth compared to SNMPv2c. Keep this in mind in case of SNMP traffic over the Radio channel.

Wherever possible, use the RipEX Ethernet interface for SNMP communication to free up the radio channel.

[Note]Note

There are many Network Management Systems available on the market. Whichever you choose, keep in mind the described limitations. E.g. never use NMS, which can download only the entire remote device MIB and not single OIDs.

2.1.2. Bandwidth Efficiency Tip

If you wish to monitor many watched values (VSWR, Temperature, UCC, …) from remote stations connected over the radio channel and you have a star topology network, you can improve bandwidth efficiency by reading OID values only from the Master (Repeater) RipEX station.

The advantage of the above is that the watched values from remote stations are broadcast in regular intervals and saved in the Master (Repeater) RipEX. These values from neighbouring stations have their own OID’s and can be downloaded from the Master (Repeater) RipEX.

In the picture below – Master RipEX station periodically reads watched values from its neighbouring Slave stations. Whenever the NMS requests any value mentioned, the reply is sent only from the Master station (over Ethernet) saving radio bandwidth. SNMP uses radio link only for sending SNMP Traps from any Slave to the NMS.

[Note]Note

The diagram is simplified – there are no flows for SNMPv3 PDUs, neither Inform’s Acknowledgments.

NMS communication with Slave stations

Fig. 2.1: NMS communication with Slave stations

[Note]Note

In such a case, watched values from neighbouring stations are displayed as part of the Master (Repeater) station.

The OID of individual remote stations is based on the order in the Neighbours menu of RipEX web interface (i.e. 1st neighbour has the last OID digit set to 1, 2nd neighbour to 2, etc.). Due to its dynamic character, it may happen that the order might be changed each period (e.g. once a day), keep this in mind!

[Important]Important

To avoid this confusion, using Zabbix “dynamic indexes” is suggested. See the Section 3.2.3, “Reading Remote Watched Values” for more details about dynamic indexes and their usage with RipEX units.

2.2. RipEX SNMP Settings

SNMP agent is switched off by default. To enable it, go to the settings menu and click on the SNMP button.

[Important]Important

Thresholds for all SNMP traps/informs can be configured in the RipEX web interface, Settings → Alarm management. Since detailed description of RipEX SNMP settings can vary based on the current firmware, please kindly refer to the online Help accessible through the RipEX web interface or see the User manual, Chapter Settings
(https://www.racom.eu/eng/products/m/ripex/h-menu.html#settings).

2.3. RipEX Traps/informs Description

The traps/informs are sent whenever any of the following watched values are beyond their threshold ranges:

  • RSS (Received Signal Strength)

  • DQ (Data Quality)

  • TX Lost (The probability of a transmitted frame being lost)

  • UCC (Power voltage [V])

  • Temperature [C]

  • RF Power [W]

  • VSWR (Voltage Standing Wave Ratio, 1.0 = the best ratio, 1.0 – 1.8 = acceptable ratio, > 2.5 = indicates a serious problem in antenna or feeder)

  • Ethernet RX/TX Packets ratio (Ratio between received and sent packets over Ethernet)

  • COM1/2 RX/TX Packets ratio (Ratio between received and sent packets over COM ports)

  • HW Alarm input

  • Hot-Standby (SNMP trap containing active station identity – sent by the active station)

  • Backup paths system (Backup path state and Alternative path state changes)

  • Unit ready (the hardware alarm output or the SNMP trap indicates that the RipEX radio is ready to operate)