Cisco Nexus 3548 - SPAN and ERSPAN Sampling

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
•
The span-threshold least value has been updated from 0 to 2. When you set the span-threshold to a lowest
value of 2, the SPAN buffer occupied is 528. When you use the negate command no hardware profile
buffer span-threshold 2, the span-threshold value is 208. The default value is lesser then the least value
of span-threshold.
•
When a source interface in a SPAN session is operationally down, then that SPAN session will not go
operationally down. This behavior does not impact any functionality.
•
SPAN filtering supports only 16 filters. These filters can be a combination of VLAN-based, IP-based,
and MAC-based filters.
•
When a SPAN session is configured with a multicast router port being the source port, the destination
port sees all the multicast traffic even when there is no traffic that is actually being forwarded to the
source port. This is due to a current limitation of the multicast/SPAN implementation.
•
SPAN filtering is applicable for all the traffic of the switch except the SPAN source interface traffic.
•
You can configure only one IP-based, one MAC-based and one VLAN-based filter per SPAN session.
•
The number of filters is further restricted by the number of SPAN sessions and the type of source as
follows:
◦
A maximum of 8 MAC-based, 8 IP-based or 8 VLAN-based filters can be configured.
◦
A maximum of 4 IP-based, 4 MAC-based or 4 VLAN-based filters can be attached to all
interface-based SPAN sessions.
◦
A maximum of 8 IP-based, 8 MAC-based or 8 VLAN-based filters can be attached to all
VLAN-based SPAN sessions.
•
Filters can be used only in the ingress direction. This is not configurable.
•
A SPAN session must be up to for filters to work.
•
You cannot configure filters on ERSPAN-dst sessions.
•
You cannot configure filters on Warp SPAN sessions.
SPAN and ERSPAN Sampling
Cisco NX-OS Release 6.0(2)A4(1) supports sampling of source packets for each SPAN or ERSPAN session.
Monitoring only a sample number of source packets helps reduce SPAN or ERSPAN bandwidth. This sample
is defined by a range that you can configure. For example, if you configure the range as 2, 1 out of every 2
source packets will be spanned. Similarly, if you configure the range as 1023, 1 out of every 1023 packets
will be spanned. This method provides an accurate count of SPAN or ERSPAN source packets, but it does
not include any time-related information about the spanned packets.
Cisco Nexus 3548 Switch NX-OS System Management Configuration Guide, Release 6.x
144
Configuring SPAN
SPAN and ERSPAN Sampling