Install Guide

The port monitoring or mirroring function when applied to VLT devices works as expected except with some restrictions. You
can configure RPM or ERPM monitoring between two VLT peers. As VLT devices are seen as a single device in the network,
when a fail over occurs, the source or destination port on one of the VLT peers becomes inactive causing the monitoring session
to fail. As a result, Dell EMC Networking OS does not allow local Port mirroring based monitoring to be configured between VLT
peers. However, you can create local Port mirroring monitoring sessions separately on individual devices that are a part of the
VLT configuration.
NOTE: For more information on configuring VLT, see Configuring VLT on page 919.
VLT Non-fail over Scenario
Consider a scenario where port monitoring is configured to mirror traffic on a VLT device's port or LAG to a destination port on
some other device (TOR) on the network. When there is no fail over to the VLT peer, the VLTi link (ICL LAG) also receives the
mirrored traffic as the VLTi link is added as an implicit member of the RPM vlan. As a result, the mirrored traffic also reaches the
peer VLT device effecting VLTi link's bandwidth usage.
To mitigate this issue, the L2 VLT egress mask drops the duplicate packets that egress out of the VLT port. If the LAG status of
the peer VLT device is OPER-UP, then the other VLT peer blocks the transmission of packets received through VLTi to its port
or LAG. As a result, the destination port on the device to which the packet analyzer is connected does not receive duplicate
mirrored packets.
VLT Fail-over Scenario
Consider a scenario where port monitoring is configured to mirror traffic on the source port or LAG of a VLT device to a
destination port on an other device on the network. A fail-over occurs when the primary VLT device fails causing the secondary
VLT device to take over. At the time of failover, the mirrored packets are dropped for some time. This time period is equivalent
to the gracious VLT failover recovery time.
RPM over VLT Scenarios
This section describes the restrictions that apply when you configure RPM in a VLT set up. Consider a simple VLT setup where
two VLT peers are connected using VLTi and a top-of-rack switch is connected to both the VLT peers using VLT LAGs in a ring
topology. In this setup, the following table describes the possible restrictions that apply when RPM is used to mirror traffic:
Table 76. RPM over VLT Scenarios
Scenario RPM Restriction Recommended Solution
Mirroring an Orphan Port on a VLT LAG
— In this scenario, the orphan port
on a VLT device is mirrored to the
VLT LAG that connects a top-of-rack
(TOR) switch to the VLT device. The
packet analyzer is connected to the TOR
switch.
The bandwidth of the VLTi link is
unnecessarily used by mirrored traffic if
max rate limit value is configured in the
RPM mirror session.
Use ERPM session instead of RPM.
Mirroring an ICL LAG to Orphan Port —
In this scenario, the ICL LAG is mirrored
to any orphan port on the same VLT
device. The packet analyzer is connected
to the local VLT device through the
orphan port.
No restrictions apply. If the packet analyzer is directly
connected to the VLT device, use local
Port mirroring session instead of RPM.
Mirroring an ICL LAG to the VLT LAG —
In this scenario, the ICL LAG is mirrored
to the VLT LAG on the same VLT device.
Packet analyzer is connected to the
TOR.
No restrictions apply. None.
Mirroring VLT LAG to Orphan Port — In
this scenario, the VLT LAG is mirrored to
an orphan port on the same VLT device.
No restrictions apply. If the packet analyzer is directly
connected to the VLT device, use local
Port mirroring session instead of RPM.
660 Port Monitoring