Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual page 302

Configuring UDE and UDLR
UDE Configuration Guidelines
When configuring UDE, follow these guidelines:
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Configuring Hardware-Based UDE
There are no software configuration procedures required to support hardware-based UDE. Install a
unidirectional transceiver to implement hardware-based UDE.
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
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STP cannot prevent Layer 2 loops in topologies that include unidirectional links.
Send-only ports always transition to the STP forwarding state, because send-only ports never receive
BPDUs.
Receive-only ports cannot send BPDUs.
Unidirectional ports do not support any features or protocols that require negotiation with the port
at the other end of the link, including these:
Speed and duplex mode autonegotiation
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Link negotiation
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IEEE 802.3Z flow control
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Dynamic trunking protocol (DTP)
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You must manually configure the parameters that are typically controlled by Layer 2 protocols.
A topology that includes unidirectional links only supports the VLAN Trunking Protocol (VTP)
when the VTP server can send VTP frames to all switches in the VTP domain.
Disable VTP pruning on switches that have send-only ports, because VTP pruning depends on a
bidirectional exchange of information.
Unidirectional EtherChannels cannot support PAgP or LACP. To create a unidirectional
EtherChannel, you must configure the EtherChannel "on" mode.
You can configure software-based UDE on the physical ports in an EtherChannel. You cannot
configure software-based UDE on any nonphysical interfaces (for example, port-channel
interfaces).
When you implement hardware-based UDE on a port or configure software-based UDE on a port,
UDLD is automatically disabled on the port.
CDP sends CDP frames from send-only ports and receives CDP frames from receive-only ports,
which means that the switch on the send-only side of a unidirectional link never receives CDP
information.
SPAN does not restrict configuration of unidirectional ports as sources or destinations.
– Send-only ports can be SPAN destinations.
Receive-only ports can be SPAN sources.
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Unidirectional ports do not support IEEE 802.1X port-based authentication.
IGMP snooping does not support topologies where there are unidirectional links between the switch
and the hosts that are receiving multicast traffic.
Configure UDLR with UDE to support communication over unidirectional links between IGMP
snooping on the switch and a multicast router.
Unidirectional links do not support ARP.
Chapter 20 Configuring UDE and UDLR
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