• Tap Aggregration Tip: Popping MPLS tags for Untagged or VLAN based Tools

 
 
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In Tap Aggregation scenarios common in WAN and Service Provider environments, MPLS tags are present.  Many of the analysis tools do not understand these tags and so the Arista DANZ feature set allows for these to be removed.  This functionality has been around since 4.15.0F however initially had the limitation that the traffic would always be sent out the Tool port with a VLAN tag.  However, some tools not only do not understand MPLS, but also VLAN tags, so this tip describes how to deal with both 802.1q and untagged scenarios.

Step 1:  Configure MPLS pop/strip on the Tap port:

(conf-if-Et1)#switchport tap mpls pop all

Step 2:  Determine if the Analysis Tool is capable of handling VLAN traffic or not.  

a) If not, and Untagged traffic must be sent, then nothing else needs to be configured.  Ethernet frames will be sent with Ethertype 0x8000 without any dot1q tags.

b) If VLAN tags are desired, then the identity tag can be defined on the tap port and enabled on the tool port:

(conf-if-Et1)#switchport tap identity X

where X is the VLAN tag desired, will default to 1 if not configured

(conf-if-Et2)#switchport tool switchport tool identity dot1q

Note that the VLAN tagging procedure can also be done via Traffic Steering policies instead of right on the Tap port – please consult the resources on EOS Central or Arista documentation.

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