In-Line Installation

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This section describes the Allegro Network Multimeter In-Line installation.



Allegro recommends a separate Tap, a Packet Broker or Mirror Port for productive network links. Please use the In-Line only if the failure of a link does not cause problems.

What is the In-Line mode?

The In-Line mode allows the Allegro to work as a transparent Bridge. Pairs of network ports form a group where all received traffic is forwarded immediately to the other port of the pair. It is the default configuration of the Allegro Network Multimeter that 2 port pairs build a transparent Bridge.

How should the In-Line mode be used?

The Allegro can be installed between 2 network devices. As an example, the Allegro can be installed between a Switch and an Access Point. The In-Line mode is designed for links where the downtime of a link is not critical and where a delay and jitter of a few microseconds is acceptable. See #Limitations for more details.

How do I configure the In-Line mode?

The In-Line mode can be configured at SettingsGlobal settingsPacket processing mode. The interfaces can be configured to Bridge mode or Sink mode. The Bridge mode will enable packet forwarding to the Ethernet pair ports.

Bridge mode.png

Allegro Devices Bridge Pairs

Devices with built-in network ports

The Allegro 200, 500, 1000, 1200, 3000 and 3200 have built-in physical network ports which run by default in Bridge mode.

Device Picture Monitoring Ports Bridge Pairs Pair Description
Allegro 200 Allegro-200 back cut.jpg 2 1 Ports 1 and 2 establish one Bridge for the In-Line mode.
Allegro 500 Allegro-500 back cut.jpg
Allegro-500 front cut.jpg
4 2 Port pairs 1,2 and 3,4 establish two Bridges for the In-Line mode.
Allegro 1000
Allegro 3000
Allegro-1000 front cut.jpg 7 3 Port pairs 2,3, 4,5 and 6,7 establish in total 3 Bridges for the In-Line mode. The pair are the upper and lower Ethernet ports. Port 1 will receive traffic in Sink mode since there is no corresponding Bridge port.
Allegro 1200
Allegro 3200
Allegro-1200-front cut.jpg 7 3 Port pairs 2,3, 4,5 and 6,7 establish in total 3 Bridges for the In-Line mode. The pair are the upper and lower Ethernet ports. Port 1 will receive traffic in Sink mode since there is no corresponding Bridge port.
Allegro x300
Allegro x500
none none The Allegro x300 and x500 series do not have built-in network ports; see section expansion cards below.

Expansion card options

Port expansion cards

Various 1G-100G Base-T and Base-X port expansion cards, featuring RJ45, SFP+, SFP28, QSFP and QSFP28 connection options. All Allegros with network card expansion slots support the In-Line mode by default. All expansion cards have either 2 or 4 network ports. Each card forms 1 or 2 Bridges. On expansion cards with 4 ports, the two left and the two right ports are the Bridge pairs.

Bypass Fail-over cards

The bypass cards for the Allegro Network Multimeter deliver an optical fail-over when the software bypass is not active. The bypass will be enabled when Bridge mode is active and triggered when the Allegro firmware is not running due to power off/loss, during the firmware upgrade process and/or most other instances of software/hardware failure.

PoE provisioning cards

Power over Ethernet bypass is not supported by the Allegro. A PoE expansion card can be installed to support PoE. Alternatively a PoE injector can be used if PoE is required.

nanosecond time stamping cards

SFP+ 2-port extension cards with (GPS based) nanosecond timestamp support (100M/1G/10G)


Link setup

The Allegro negotiates every port of a Bridge pair independently. This can lead to a link speed mismatch. As an example, an installation between a 1GBit/s Switch port and a 100 MBit/s VoIP telephone will lead by default to a speed mismatch. The Allegro will show a warning if there is a speed mismatch. You can check if there is a mismatch at Interface stats.

Interface speed mismatch.png

Delay and jitter

Traffic forwarding is handled in software. This incurs a minor delay and jitter. The average delay and jitter is below 1 microsecond and does not have a measurable impact on most networks. The worst case jitter is below 50 microseconds. You can check average and worst case jitter at System infoInfoLoad.

Loop duration.png

Packet limitations

The software bypass does NOT forward :

  • Packets with an MTU above 9000 bytes
  • FcoE ( Fibre Channel over Ethernet ) packets ( ethertype 0x8906 )
  • Ethernet flow control and pause frames ( ethertype 0x8808 )

Performance limitations

The software bypass can forward several million packets per second depending on the Allegro model. If packet loss on the bridge is not accepable for multi-million packets per second, please use a Tap or similar.