Udld - Zte ZXR10 5900E Product Description

Optional TLV contains basic management TVL set (such as port description TVL),
special TLV set organized by IEEE 802.1 and special TLV set organized by IEEE 802.3.
LLDPDU end TLV indicates the end of LLDPDU.

3.2.26 UDLD

UDLD is a L2 logic link detection protocol which can detect logic connection of Ethernet
link and verify physical connection. Different from physical connection detection, UDLD
detects based on neighbors. L1 devices are transparent to UDLD.
Firstly UDLD needs to establish neighbor relationships. When an Ethernet interface with
status of UP launches UDLD, the interface sends neighbor joining Hello message to its
adjacent device. The interface launching UDLD of the adjacent device sends back an
Echo message. Receiving an Echo message indicates that the device considers the two
devices are interconnected. It establishes neighbor relationship with the peer-end and
also sends an Echo message. Receiving this Echo message by the peer-end, neighbor
relationship on the two devices are both established.
After establishing neighbor relationship, they send Hello messages regularly to check
whether the link works well. The device updates the buffered neighbor information stored
at local and reset time for neighbor timeout. If no Hello detecting message is received
until neighbor aging time, the link is considered as abnormal. Corresponding processing
will be taken based on different work mode.
There are two work modes for UDLD: common mode and aggressive mode. In common
mode, an interface is Down only when protocol packets are received confirming link
single pass. No processing will be taken at the interface if no corresponding packets are
received or link single pass cannot be affirmed. In aggressive mode, the interface is
Down as long as two-way expedite link cannot be guaranteed. The common place of
these two modes is that alarm will be printed as long as normal link status cannot be
affirmed.
Generally speaking, UDLD makes interface Down in the following situations:

In common mode, sends Hello neighbor joining message, and receives Echo
message which indicates the neighbor of the peer-end is not itself.
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ZXR10 5900E Product Description
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