Cisco Cisco Nexus 5010 Switch Libro bianco

 

 

© 2014 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information. 

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Configuration 

SPAN-on-Drop uses the existing SPAN configuration in Cisco NX-OS Software. 

The configuration examples presented below use this scenario: A lot of ports are sending data to port 3/1. At some 

point, the buffers for port 3/1 start to fill up, leading to tail drops. To identify which application is experiencing loss, 

you can configure a SPAN-on-Drop session using port 3/1 as the source, send the SPAN data to a local or remote 

host running Wireshark, and then decode all the packets that were dropped. With this approach, you can easily 

debug drops and identify the application being degraded by congestion. 

This configuration creates a SPAN session with type SPAN-on-DROP. In the following example, the source 

interface, where congestion may be present, is port e3/1. The destination port is e3/2, which must be in switchport 

monitor mode. 

switch(config)# monitor session <session_number> type SPAN-on-DROP 

switch(config-SPAN-on-DROP)# source interface e3/1 

switch(config-SPAN-on-DROP)# destination interface e3/2 

This configuration creates a SPAN session with type SPAN-on-DROP-erspan. In the following example, the 

source interface, where congestion may be present, is port e3/1. The destination port is a remote host with IP 

address 100.1.1.2. 

switch(config)# monitor session <session_number> type SPAN-on-DROP-erspan 

switch(config-SPAN-on-DROP-erspan)# source interface e3/1 

switch(config-SPAN-on-DROP-erspan)# destination ip 100.1.1.2 

Note:   The destination port configuration and restrictions are the same as for a local SPAN session. Access 
control list (ACL)-based SPAN is not supported for SPAN-on-Drop sessions. Maximum transmission unit (MTU) 

truncation also is not supported with SPAN-on-Drop. 

To verify that the monitor session was correctly configured, use the command show monitor session 

<session_number>. 

Feature Guidelines 

Note the following guidelines when using the SPAN-on-Drop feature: 

● 

The feature works for unicast packets and not multicast because packet drops can be monitored on ingress 

only. For Multicast, packets are dropped at Egress in case of congestion. 

● 

The source interfaces can only be Ethernet, although they can be part of a PortChannel. Sources also can 

be a part of a SPAN-on-Drop session and a local SPAN session simultaneously. Fabric extender (HIF) 

interfaces are not supported as sources; however, fabric (NIF) interfaces are supported. Setting a fabric 

interface as a source allows SPAN-on-Drop to be enabled on all fabric extender ports associated with that 

fabric interface. 

● 

Only one SPAN-on-drop or SPAN-on-drop ERSPAN session can be active at a time. However, you can 

have multiple source ports and multiple destination ports. Source ports can be part of a SPAN-on-Drop 

session and a local SPAN session simultaneously.