• LLDP on Tap ports

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As of EOS 4.14.0F for Arista 7150 line of switches and EOS 4.20.1F for Arista 7500/7280 lines of switches, users of the tap aggregation features can benefit from visibility gained from LLDP on tap ports. Neighbor information will now be processed by the CPU and made available via the EOS CLI. Allows the tap aggregation administrator to view neighbor information for verification and troubleshooting.

This article details the use of LLDP neighbor information on tap ports in tap aggregation exclusive mode. Show LLDP commands work in Tap Aggregation Exlcusive mode as they do in normal switching mode, no configuration is required for 7150 line of switches, but for 7500/7280 lines of switches, a global configuration, ‘protocol lldp trap’, is needed to enable trapping LLDP packets to CPU. Since tap ports can only receive traffic, they will not send LLDP information to their neighbors.

Note: The LLDP packets are processed by the CPU of the tap aggregation device to provide neighbor information for the convenience described above. On 7150 lines of switches, the LLDP packets are also passed from the tap to tool ports. This allows the information to also be useful by the tool servers attached to tool ports as well.  However, on 7500/7280 lines of switches, there is a limitation that when CPU trap LLDP packets is turned on, tool ports can no longer receive LLDP packets. 


Command examples

In this example, note interface ethernet 17 is a tap mode interface, and ethernet 1 & 2 are tool mode interfaces.

7150s#show interfaces status

Port       Name              Status       Vlan        Duplex  Speed Type
Et1                          connected    tool          full    10G 10GBASE-CR
Et2                          connected    tool          full    10G 10GBASE-CR
Et17                         connected    tap           full    40G 10GBASE-SR

Next, we issue the show lldp neighbor command. Note that we see neighbor device ID 7050S attached via its interface ethernet 48.

7150s#show lldp neighbor
Last table change time   : 0:01:02 ago
Number of table inserts  : 9
Number of table deletes  : 7
Number of table drops    : 0
Number of table age-outs : 4

Port       Neighbor Device ID             Neighbor Port ID           TTL
Et17       7050S                          Ethernet48                 30

On 7500/7280, there is a global configuration under tap aggregation mode to enable/disable receiving LLDP packets on tap/tool ports.

(config-tap-agg)# protocol lldp trap 
(config-tap-agg)# no|default protocol lldp trap 



With the addition of LLDP packet processing, the tap aggregation switch can now leverage neighbor information on the aggregation switch itself. This gives the operator the ability to verify connectivity that exists matches what is expected during setup and troubleshooting. On 7150 line of switches, the LLDP packets are also passed from tap to tool ports, providing the ability for tools attached to benefit from this information as well, but for 7500/7280 lines of switches, when CPU trap for LLDP packets is turned on, tool ports can no longer receive LLDP packets.


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