Chapter 40 ZULD
GS2220 Series User’s Guide
354
C HAPTER 40
ZULD
40.1 ZULD O ve rvie w
A unidirectional link is a connection where the link is up on both ends, but only one end can receive
packets. This may happen if OAM was initially enabled but then disabled, there are mis-configured
transmitting or receiving lines or the hardware is malfunctioning. Zyxel Unidirectional Link Detection
(ZULD) is a layer-2 protocol that can detect and disable these physical one-way links before they cause
loops or communication malfunction.
In the figure below, S1–A is a bidirectional link as both ends can send packets to each other. S1–B is
unidirectional as B cannot send packets to S1 (although the S1–B link is up). Similarly, S2–S1 is
unidirectional as S1 cannot send packets to S2 (although the S1–S2 link is up).
Fig ure 267 ZULD Overview
40.1.1 Wha t You C a n Do
• Use the ZULD Sta tus screen (
Section 40.2 on page 355) to see details on ZULD.
• Use the ZULD Co nfig ura tio n screen (
Section 40.3 on page 356) to enable ZULD on a port, configure a
mode and set the probe time.
40.1.2 Wha t You Ne e d to Kno w
• ZULD must be enabled on the Switch and the ports in order to detect unidirectional links by monitoring
OAMPDUs.
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