Cisco Nexus 5000 Series and Cisco Nexus 2000 Series Release Notes, for Cisco NX-OS Release 5.0(2)N1(1) and NX-OS Release 5.0(2)N2(1) OL-22747-02, December 2010)

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Cisco Nexus 5000 Series and Cisco Nexus 2000 Series Release Notes, for Cisco NX-OS Release 5.0(2)N1(1) and NX-OS Release 5.0(2)N2(1)
OL-22747-02
Limitations
The correct VLAN tag is applied on the frame as it goes out the SPAN destination. The only
exception is if frames ingress on a SPAN source port on an invalid VLAN. In this case, vlan 0 is
applied on a spanned frame.
• Spanned FCoE frames do not preserve original SMAC and DMAC fields. The Ethernet header gets
modified as the frame is spanned to the destination. The modified header fields are displayed when
monitored on the SPAN destination.
• The CoS value in spanned FCoE frames on the Ethernet SPAN destination port does not match with
the CoS value in the SPAN FCoE source frame. The CoS value on the captured SPAN FCoE frame
should be ignored.
• The class-fcoe cannot be removed even if Fibre Channel is not enabled on a switch.
• If a port drains traffic at a rate less than 100 Kbps, it is errdisabled in 10 seconds to avoid buffer
exhaustion. However, if the drain rate is larger than 100 Kbps, the port may not be consistently
errdisabled within 10 seconds which exhaust ingress buffers and discard frames. Use the shut
command to disable the slow-draining port.
• The multicast storm control functionality in the Cisco Nexus 5000 Series does not distinguish
between IP, non-IP, registered, or unregistered multicast traffic. All multicast traffic is subject to a
single-multicast storm control policer when configured.
SPAN Limitations on Fabric Extender Ports
This section describes the SPAN limitations on Fabric Extender ports.
• Ports on a FEX can be configured as a tx-source in one session only.
If two ports on the same FEX are enabled to be tx-source, the ports need to be in the same session.
If you configure a FEX port as a tx-source and another port belonging to the same FEX is already
configured as a tx-source on a different SPAN session, then a error is displayed on the CLI.
In the following example, Interface Ethernet100/1/1 on a FEX 100 is already configured as a
tx-source on SPAN session-1:
swor28(config-monitor)# show running-config monitor
version 4.0(1a)N2(1)
monitor session 1
source interface Ethernet100/1/1 tx
destination interface Ethernet1/37
no shut
If you add an interface Ethernet100/1/2 as a tx-source to a different SPAN session (session-2) the
the following error is displayed:
swor28(config)# monitor session 2
swor28(config-monitor)# source interface ethernet 100/1/2 tx
ERROR: Eth100/1/2: Ports on a fex can be tx source in one session only
swor28(config-monitor)#
• When a FEX port is configured as a tx-source, the multicast traffic on all VLANs for which the
tx-source port is a member, is spanned. The FEX port sends out only multicast packets that are not
filtered by IGMP snooping. For example, if FEX ports 100/1/1-12 are configured on VLAN 11 and
the switch port 1/5 sends multicast traffic on VLAN 11 in a multicast group, and hosts connected to
FEX ports 100/1/3-12 are interested in receiving that multicast traffic (through IGMP), then that
multicast traffic goes out on FEX ports 100/1/3-12, but not on 100/1/1-2.
If you configure SPAN Tx on port 100/1/1, although the multicast traffic does not egress out of port
100/1/1, the SPAN destination does receive that multicast traffic, which is due to a design limitation.