Chapter 44 ZULD
XGS4600 Series User’s Guide
422
CHAPTER 44
ZULD
44.1 ZULD Overview
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).
Figure 338 ZULD Overview
44.1.1 What You Can Do
• Use the ZULD Status screen (Section 44.2 on page 423) to see details on ZULD.
• Use the ZULD Configuration screen (Section 44.3 on page 425) to enable ZULD on a port, configure a
mode and set the probe time.
44.1.2 What You Need to Know
• ZULD must be enabled on the Switch and the ports in order to detect unidirectional links by monitoring
OAMPDUs.
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