ERSPAN Installation

This section describes the ERSPAN installation for the Allegro Network Multimeter. ERSPAN is the abbreviation for Encapsulated Remote Switch Port Analyzer. It is switch feature that encapsulates traffic into an IP/GRE tunnel.

General

What is the ERSPAN mode

The Allegro Network Multimeter works in the mirror port mode as a traffic receiving device that . It will NOT send any traffic on the measurement Ethernet ports.

How should the ERSPAN mode be used

The ERSPAN quality depends on the switch performance and the bandwidth and latency between the switch and the Allegro.

The data plane ports of the Allegro should be connected in the mirror port mode to one or multiple mirror ports on a switch. The management port of the Allegro shall be connected to a regular switch port or to the out-of-band management switch.

See #Limitations for more details.

Where can I configure the Mirror Port Mode

Please refer to you switch manual how to set up a switch port as mirror port.

The Mirror Port Mode for the Allegro can be configured at Settings → Global Settings → Packet processing mode. The Interfaces can be configured to Bridge Mode or Sink Mode. The Sink Mode will disable the packet forwarding and sending on the Ethernet ports. Please switch to Sink Mode and save the settings at the bottom of the page

Data Plane Ports of Allegro Network Multimeters

Devices with built-in Network Ports

The Allegro 200, 500, 1000, 1200, 3000 and 3200 have built-in physical network ports.

Device	Picture	Number of Monitoring Ports	Remarks
Allegro 200		2
Allegro 500		4
Allegro 1000 Allegro 3000		7	Can be extended by extension cards.
Allegro 1200 Allegro 3200		7	Can be extended by extension cards.
Allegro x300 Allegro x500		none	The Allegro x300 and x500 series do not have built-in network ports, see section extension cards below.

Devices with port extension cards

All Allegros with network card extension slots support the Mirror Port Mode. All extension cards have either 2 or 4 network ports.

Bypass extension cards

The bypass cards for the Allegro Network Multimeter deliver a fail-over when the software bypass is not active in Bridge Mode ( see In-Line Installation for more details ). The bypass is deactivated when the When the Mirror Port Mode / Sink Mode is active.

Grouping of multiple Links ( Trunk vs. separate links )

By default, the Allegro processes all incoming traffic as one big pipe and it does not use the port as an criteria to separate links. If you have connected separate links at the Allegro, please use the virtual link grouping feature to specify which ports belong together.

This feature can also be used to forward multiple links with a packet broker to one Allegro port with VLANs as a separation.

Limitations

Switch Limitations

Please be aware that the Allegro Network Multimeter can only analyze packets that have been forwarded by the switch port. Please also be aware that the exact packet timing and ordering depends on the switch implementation. Allegro recommends the installation of a TAP to prevent any switch side effects.