Cisco Nexus 5000 Series Release Notes for Release 5.0(3)N2(2) (June 2011)

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Cisco Nexus 5000 Series and Cisco Nexus 2000 Series Release Notes, for Cisco NX-OS Release 5.0(3)N2(2) and Release 5.0(3)N2(1)
Limitations
SPAN Limitations on Fabric Extender Ports
The SPAN limitations on Fabric Extender ports are as follows:
• On a Cisco Nexus 5000 Series switch, if the SPAN source is a FEX port then the frames will always
be tagged when leaving the SPAN destination.
• On a Cisco Nexus 5010 switch or a Nexus 5020 switch, if the SPAN source is an access port on a
switch port or FEX port, the spanned frames at the SPAN destination will be tagged.
• On a Cisco Nexus 5010 switch or a Nexus 5020 switch, if the span source is an access port on a
switch port or FEX port, the spanned frames at the SPAN destination will be tagged.
• On a Cisco Nexus 5500 Platform switch, if the SPAN source is on an access port on the switch port,
then the frames will not be tagged when leaving the SPAN destination.
• 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.
• When a FEX port is configured as both SPAN rx-source and tx-source, the broadcast, non-IGMP
Layer-2 multicast, and unknown unicast frames originating from that port may be seen twice on the
SPAN destination, once on the ingress and once on the egress path. On the egress path, the frames
are filtered by the FEX to prevent them from going out on the same port on which they were
received. For example, if FEX port 100/1/1 is configured on VLAN 11 and is also configured as
SPAN rx-source and tx-source and a broadcast frame is received on that port, the SPAN destination
recognizes two copies of the frame, even though the frame is not sent back on port 100/1/1.
• A FEX port cannot be configured as a SPAN destination. Only a switch port can be configured and
used as a SPAN destination.