ZyXEL Communications MES3500-24F User Manual

Chapter 8 Basic Setting

MES3500-24/24F User’s Guide

VLAN also increases network performance by limiting broadcasts to a smaller and more 
manageable logical broadcast domain. In traditional switched environments, all broadcast packets 
go to each and every individual port. With VLAN, all broadcasts are confined to a specific broadcast 
domain. 

Note: VLAN is unidirectional; it only governs outgoing traffic.

See 

 for information on port-based and 802.1Q tagged VLANs. 

To block traffic between two specific ports within the Switch, you can use port isolation or private 
VLAN (see 

 for more information). However, it does not work across 

multiple switches. For example, broadcast traffic from isolated ports on a switch (say B) can be 
forwarded to all ports on other switches (A and C), including the isolated ports.

Smart isolation allows you to prevent isolated ports on different switches from transmitting traffic 
to each other. After you enable RSTP/MRSTP and smart isolation on the Switch, the designated 
port(s) will be added to the isolated port list. In the following example, switch A is the root bridge. 
Switch B’s root port 7 connects to switch A and switch B’s designated port 8 connects to switch C. 
Traffic from isolated ports on switch B can only be sent through non-isolated port 1 or root port 7 to 
switch A. This prevents isolated ports on switch B sending traffic through designated port 8 to 
switch C. Traffic received on designated port 8 from switch C will not be forwarded to any other 
isolated ports on switch B. 

Isolated ports: 2~6
Root port: 7
Designated port: 8

Isolated ports: 2~6
Root port: 7
Designated port: 8

Before Smart Isolation:

Isolated ports: 2~6, 8
Root port: 7
Designated port: 8

After Smart Isolation: