Concept Guide

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:
Table 73. 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 trac if max
rate limit value is congured 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. The
packet analyzer is connected to the 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.
Port Monitoring 723