Deployment Guide

Port Monitoring on VLT
Devices on which VLT is congured are seen as a single device in the network. You can apply port monitoring function on the VLT devices
in the network.
Port monitoring enables ingress or egress trac traversing on a port to be sent to another port so that the trac can be analyzed. The
port to which trac is sent for analysis is called the mirroring port. This port is connect to a port analyzer, which performs the trac
analysis function.
Depending up on the location of the port to which the port analyzer is connected, port monitoring is classied into three categories: local
Port mirroring, remote port mirroring (RPM), and encapsulated remote port mirroring (ERPM).
NOTE: For more information on port monitoring, see Conguring Port Monitoring.
The port monitoring or mirroring function when applied to VLT devices works as expected except with some restrictions. You can congure
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 Networking OS
does not allow local Port mirroring based monitoring to be congured between VLT peers. However, you can create local Port mirroring
monitoring sessions separately on individual devices that are a part of the VLT conguration.
NOTE: For more information on conguring VLT, see Conguring
VLT.
VLT Non-fail over Scenario
Consider a scenario where port monitoring is congured to mirror trac 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 trac as the
VLTi link is added as an implicit member of the RPM vlan. As a result, the mirrored trac also reaches the peer VLT device eecting 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 congured to mirror trac 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 congure 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 trac:
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Port Monitoring