In-Line Installation

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

General

DISCLAIMER

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 problem.

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.

Where can I configure the In-Line Mode

The In-Line Mode can be configured at Settings → Global Settings → Packet processing mode. The Interfaces can be configured to Bridge Mode or Sink Mode. The Bridge Mode will enable the packet forwarding to the pair ethernet port.

Bridge Pairs of Allegro Devices

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		2	1	Port 1 and 2 build one the bridge for the In-Line Mode.
Allegro 500		4	2	The port pairs 1,2 and 3,4 build the two bridges for the In-Line Mode.
Allegro 1000 Allegro 3000		7	3	The port pairs 2,3, 4,5 and 6,7 build in total 3 bridges for the In-Line Mode. The pair is the upper and lower ethernet port. The port 1 will receive traffic in sink mode as there no corresponding bridge port.
Allegro 1200 Allegro 3200		7	3	The port pairs 2,3, 4,5 and 6,7 build in total 3 bridges for the In-Line Mode. The pair is the upper and lower ethernet port. The port 1 will receive traffic in sink mode as there 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 extension cards below.

Devices with port extension cards

All Allegros with network card extension slots support the In-Line Mode by default. All extension cards have either 2 or 4 network ports. Each card forms 1 or 2 brides. On extension cards with 4 ports, the two left and the two right port as the bride pair.

Bypass extension cards

The bypass cards for the Allegro Network Multimeter deliver a fail-over when the software bypass is not active. The bypass will be enabled when the bridge mode is active when the Allegro Firmware is not running due power off, firmware upgrade process or most situations of software or hardware failure.

PoE extension cards

Power over Ethernet bypass is not supported by the Allegro. A PoE extension card can be installed to support PoE. The usage of a PoE injector is recommended if PoE is required.

Limitations

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 of there is a speed mismatch. You can check if there is a mismatch at Interface Stats.

Delay and Jitter

The traffic forwarding is done in software. This implies a delay and jitter. The average delay and jitter is below 1 microsecond and does not have ameasurable impact on most networks. The worst case jitter is below 50 microseconds. You can check your average and worst cast jitter at System Info → Info → Load.

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. If a packet loss on the bridge is not accepable for multi-million packets per second, please use a tap or similar.