Segment Links into Groups

Allegro Network Multimeter feature: virtual link groups

In this blog post you will learn important details about the Allegro Network Multimeter 'Virtual link groups' feature and how it can be used to segment a network quickly and conveniently for easy analysis.

By default, the Allegro Network Multimeter processes all combined packets, which is no problem even with Link Aggregation Control Protocol (LACP). For analysis, it does not matter which interface the packet comes from. To view several different networks separately, traffic can be grouped into virtual links. Since Release 2.4 it is possible to configure the Allegro Network Multimeter to separately view up to 100 links.

The "Virtual link groups" feature can be found in the Dashboard under "Settings" → "Virtual Link Groups". A detailed configuration guide can be found in the Product Wiki.

Feature Virtual link groups
Feature virtual link groups in the Allegro Dashboard

When segmenting the links, keep in mind that each packet will be part of a single link group only. To avoid double allocation of packets, the packet will always be assigned to the first matching group only. If overlapping links should be grouped, the "IP Groups" module can be used.

If the Allegro Network Multimeter is looking at more than one link at a time, the analysis will treat each link separately. For example, if a packet is present multiple times but on different links, it is not a retransmission. Only if this happens twice on the same link is it one.

Examples for virtual link groups
Examples for virtual link groups

What is meant by a link for this feature? There are currently four types of configuration:

  • Interface port: all interfaces belong to the group
  • MPLS tags: MPLS links are segmented and viewed
  • VLAN tags: virtual networks can be viewed completely separately
  • ERSPAN ID: GRE tunnels can be segmented and viewed separately

Specifically, the last two points are interesting in connection with Packet Brokers. You can route all existing links, via an aggregated link, to an Allegro Network Multimeter and add a VLAN tag per tapped link. This makes it possible to separate the physical links via the VLAN tag.

The 'Virtual link groups' function is available in all Allegro Network Multimeters. This means that you can measure with the Allegro 500 before and after the router if you have two mirror ports. This feature also works with the larger devices like the Allegro x510 Series.

This feature is useful for different use cases:

Examples of use for device under test:

  • Measure the path behind or in front of a router simultaneously.
  • View multiple mirror ports with packet duplication by switching or routing.
  • Two separate connections to be considered separately.

Concrete application example:

One mirror port has been set up as the link group 'Mirror Switch' and two ports have been set up to install the Allegro Network Multimeter inline in a PC network port. These are configured as separate link groups. On the Allegro Network Multimeter Dashboard you can then see that both the mirror port and the two PC ports have traffic. Here you can see in more detail which traffic is generated by each group.

Overview of the network traffic of individual groups
Overview of the network traffic of individual groups

The traffic between the different groups is handled in a logically separated manner. This can be seen, among other things, by the IP addresses that were accessed. If you look at them for the concrete PC, there are far less IP-addresses visible than at the mirror-port. So you can easily view several links in parallel.

Comparison of IP addresses between mirror switch and PC
Comparison of IP addresses between mirror switch and PC

For more information on this topic, please watch the video (in German with English subtitles) or visit our Product Wiki.

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