Skip to main content
Sign Out

Welcome to Dell

My Account
  • Place orders quickly and easily
  • View orders and track your shipping status
  • Enjoy members-only rewards and discounts
  • Create and access a list of your products
  • Manage your Dell EMC sites, products, and product-level contacts using Company Administration.
Sign In Create an Account Dell Financial Services Premier Sign In Partner Program Sign In
Contact Us

Your Dell.com Carts

Dell Configuration Guide for the S4048–ON System 9.14.2.4

PDF

Port Monitoring on VLT

Devices on which VLT is configured 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 traffic traversing on a port to be sent to another port so that the traffic can be analyzed. The port to which traffic is sent for analysis is called the mirroring port. This port is connect to a port analyzer, which performs the traffic analysis function.

Depending up on the location of the port to which the port analyzer is connected, port monitoring is classified into three categories: local Port mirroring, remote port mirroring (RPM), and encapsulated remote port mirroring (ERPM).

In VLT RPM, Dell EMC Networking OS supports only 3 Mirror-to-Port (MTPs) in hardware.

By default, 2 MTPs are used for ICL lag in VLT. The remaining one MTP is used to mirror only in one direction, either rx or tx.

NOTE For more information on port monitoring, see Port Monitoring.

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.

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 1. RPM over VLT Scenarioslocal Port mirroring Restrictions
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. 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.
Mirroring using Intermediate VLT device — In this scenario, the VLT device acts as the intermediate device in remote mirroring. The TOR switch contains the source-RPM configurations that enable mirroring of the VLT lag (of the TOR switch) to any orphan port in the VLT device. The packet analyzer is connected through the VLT device, but not directly to the VLT device. No restrictions apply None.
Mirroring Orphan Ports across VLT Devices — In this scenario, an orphan port on the primary VLT device is mirrored to another orphan port on the secondary VLT device through the ICL LAG. The port analyzer is connected to the secondary VLT device. No restrictions apply to the RPM session. The following example shows the configuration on the primary VLT device:source orphan port destination remote vlan direction rx/tx/both.The following example shows the configuration on the secondary VLT device:source remote vlan destination orphan port. None.
Mirroring VLT LAG across VLT Peers — In this scenario, the VLT LAG on the primary VLT peer is mirrored to an orphan port on the secondary VLT peer through the ICL LAG. The packet analyzer is connected to the secondary VLT peer. No restrictions apply to the RPM session. The following example shows the configuration on the primary VLT device:source VLT LAG destination remote vlan direction rx/tx/both.The following example shows the configuration on the secondary VLT device:source remote vlan destination orphan port. None
Mirroring member port of ICL LAG to Orphan Port of peer vlt device— In this scenario, a member port of the ICL LAG or a member port of the VLT LAG is mirrored to an orphan port on the peer VLT device. The packet analyzer is connected to the peer VLT device. The bandwidth of the VLTi link is unnecessarily used by mirrored traffic if max rate limit value is configured in the RPM mirror session. None.
Mirroring member port of ICL LAG to VLT LAG — In this scenario, a member port of the ICL LAG is mirrored to the VLT LAG on the same VLT device. The packet analyzer is connected to the TOR switch. No restrictions apply. The bandwidth of the VLTi link is unnecessarily used by mirrored traffic if max rate limit value is configured in the RPM mirror session. If you want to mirror traffic in the TOR locally, use local Port mirroring session instead of RPM.
Mirroring with a VLAN as source and destination — If the members of the source and destination VLANs are same in a single monitoring session. No restrictions apply. None.
Mirroring with an interface or LAG as source and destination --- If the source and destination interface or LAG of a monitor session are same. No restrictions apply. None.

Rate this content

Accurate
Useful
Easy to understand
Was this article helpful?
0/3000 characters
  Please provide ratings (1-5 stars).
  Please provide ratings (1-5 stars).
  Please provide ratings (1-5 stars).
  Please select whether the article was helpful or not.
  Comments cannot contain these special characters: <>()\