• DANZ Tap Aggregation – Basic settings – Before you start

 
 
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Several Arista switches support DANZ feature set for Tap Aggregation. The tap aggregation mode is a mere configuration (1-2 lines) that transform a high performance L2/L3 switch into a Tap Aggregator (NPB). This mode require certain considerations:

1) Tap aggregation – How to selecting the exclusive mode

That tap aggregation mode is exclusive to part of a switch of the whole switch. Parts of the switch that are excluded from the Tap Aggregation mode can work either in fully L2/L3 forwarding mode (normal switching mode), or in simple hub mode. The options available vary per platforms, as per the below list. For the latest options available, verify your manual or the DANZ TOI (Transfer of Information), as additional options would be added.

  • 7150S
    • Tap Aggregation mode applies to the whole switch
    • Some ports can be excluded to learn PTP
    • Some ports can be excluded and work in hub mode (for passthrough)
    • No L2/L3 forwarding possible.
  • 7500E
    • Tap Aggregation mode has a line card granularity
    • Some ports can be excluded to learn PTP
  • 7280SE
    • Tap Aggregation mode applies to the whole switch
    • Some ports can be excluded to learn PTP

 

The Tap aggregation exclusive mode and port exclusion should be considered before starting implementing Tap Aggregation, a switch or line card in Tap Aggregation mode is unable to perform Layer2/Layer3 learning/lookups, hence prevention conventional bridging and routing on those ports.

 

3) Undesired protocols

 

In Tap Agggregation mode, any protocols usually required in a bridged or routed network would not be desired anymore. For example: Spanning-Tree BPDU, LACP, and  IGMP snooping are not used anymore and would be even be undesired, possibly seen as noise over your original traffic if there were present.

 

Spanning-Tree

You should disable Spanning-Tree:

switch(config)#spanning-tree mode none

 

IGMP Snooping

You should disable IGMP snooping:

switch(config)#no ip igmp snooping

 

LACP

For any load-balancing requirement, port-channel are employed in static mode with a variety of load-sharing mechanisms : dynamic, symmetric, custom, etc. Whether used to distribute traffic to multiple or a single device, in no case should the port-channel be configured in dynamic mode (“auto” or “desired”) as firstly the remote tool/analyzer is unlikely to be able to established an LACP port-channel. Secondly, the original traffic might already contain some LACP frames, which would compromise the port-channel sustainability. Both the Arista tap aggregator and the remote device (tool/analyzer) should be configured for static Port-channel (mode “on”)

 

QoS

By default, every traffic is de-prioritized to the same universal class 0 as the purpose of the Tap Aggregator is to forward traffic as it arrives. This behaviour and the non-blocking hardware capabilities of the Arista switches guarantee in-sequence even at full performance, any to any port.

 

 

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