Cisco Cisco Email Security Appliance C690 User Guide

VLANs can be used to segment networks for security purposes, to ease administration, or increase 
bandwidth. VLANs appear as dynamic “Data Ports” labeled in the format of: “VLAN DDDD” where the 
“DDDD” is the ID and is an integer up to 4 digits long (VLAN 2, or VLAN 4094 for example). AsyncOS 
supports up to 30 VLANs. Duplicate VLAN IDs are not allowed on your appliance.

A physical port does not need an IP address configured in order to be in a VLAN. The physical port on 
which a VLAN is created can have an IP that will receive non-VLAN traffic, so you can have both VLAN 
and non-VLAN traffic on the same interface.

VLANs can be created on all “Data” and “Management” ports, including fiber optic data ports available 
on some appliance models.

VLANs can be used with NIC pairing (available on paired NICs) and with Direct Server Return (DSR). 

 illustrates a use case showing how two mail servers unable to communicate directly due to 

VLAN limitations can send mail through the Email Security appliance. The blue line shows mail coming 
from the sales network (VLAN1) to the appliance. The appliance will process the mail as normal and 
then, upon delivery, tag the packets with the destination VLAN information (red line).