Cisco 7604 User Manual

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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:
• UDE is supported on the Supervisor Engine 720. UDE is not supported on the Supervisor Engine 2.
• 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
– Link negotiation
– IEEE 802.3Z flow control
– Dynamic trunking protocol (DTP)
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 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.
• 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.
• 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.
• 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.
• 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.

Cisco 7604 Specifications

General

Brand	Cisco
Model	7604
Category	Network Router
Language	English