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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 23 Configuring UDE and UDLR
Configuring UDE and UDLR
UDE Configuration Guidelines
When configuring UDE, follow these guidelines:
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UDE is supported on the Supervisor Engine 720. UDE is not supported on the Supervisor Engine 2.
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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.
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Unidirectional ports do not support any features or protocols that require negotiation with the port
at the other end of the link, including these:
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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)
You must manually configure the parameters that are typically controlled by Layer 2 protocols.
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A topology that includes unidirectional links only supports the VLAN Trunking Protocol (VTP)
when the VTP server can send VTP frames to all routers in the VTP domain.
•
Disable VTP pruning on routers 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.
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CDP sends CDP frames from send-only ports and receives CDP frames from receive-only ports,
which means that the router on the send-only side of a unidirectional link never receives CDP
information.
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SPAN does not restrict configuration of unidirectional ports as sources or destinations.
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Send-only ports can be SPAN destinations.
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Receive-only ports can be SPAN sources.
•
Unidirectional ports do not support IEEE 802.1X port-based authentication.
•
IGMP snooping does not support topologies where there are unidirectional links between the router
and the hosts that are receiving multicast traffic.
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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.
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.