Characteristics of Destination Ports
Each local SPAN session must have a destination port (also called a monitoring port) that receives a copy of
traffic from the source ports or VLANs. A destination port has these characteristics:
• Can be any physical port. Source Ethernet and FCoE ports cannot be destination ports.
• Cannot be a source port.
• Cannot be a port channel.
• Does not participate in spanning tree while the SPAN session is active.
• Is excluded from the source list and is not monitored if it belongs to a source VLAN of any SPAN session.
• Receives copies of sent and received traffic for all monitored source ports.
• The same destination interface cannot be used for multiple SPAN sessions. However, an interface can
act as a destination for a SPAN and an ERSPAN session.
SPAN and ERSPAN Filtering
A SPAN or ERSPAN session can be used to monitor all the traffic on all the source interfaces. This volume
of traffic can cause packet drops if there are congestions or if the destination bandwidth is not enough to
monitor all the traffic.
Cisco NX-OS Release 6.0(2)A4(1) provides the ability to filter out specific SPAN or ERSPAN traffic flows
that must be monitored. Filtering is achieved by creating a filter and attaching it to a SPAN or ERSPAN
session. Only the packets that match the filter are mirrored.
Filtering can be of the following types:
• MAC-based
• IP-based
• VLAN-based
Guidelines and Limitations for SPAN and ERSPAN Filtering
SPAN and ERSPAN filtering have the following guidelines and limitations:
• Cisco Nexus 3500 Series switches drop the SPAN copies while spanning an interface in the rx direction
and another interface in the tx direction when the traffic starts. It happens due to the default SPAN
threshold limit being low and it cannot handle the burst traffic for SPAN. Use the CLI command hardware
profile buffer span-threshold <xx> to increase the SPAN threshold.
Increasing the SPAN threshold affects the shared buffer allocation. It allocates
the SPAN buffers from the shared buffer pool.
Note
Cisco Nexus 3548 Switch NX-OS System Management Configuration Guide, Release 7.x
135
Configuring SPAN
Characteristics of Destination Ports
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