Cisco IronPort AsyncOS 7.5 for Email Configuration Guide
AppendixB Assigning Network and IP Addresses
The Cisco IronPort appliance must always be able to identify a unique interface
over which a packet will be delivered. To make this decision, the Cisco IronPort
appliance uses a combination of the packet’s destination IP address, and the
network and IP address settings of its Ethernet interfaces. The following table
summarizes the preceding examples:
Strategies for Connecting Your Cisco IronPort
Keep these things in mind when connecting your Cisco IronPort appliance:
Administrative traffic (CLI, web interface, log delivery) traffic is usually
small compared to email traffic.
If two Ethernet interfaces are connected to the same network switch, but end
up talking to a single interface on another host downstream, or are connected
to a network hub where all data are echoed to all ports, no advantage is gained
by using two interfaces.
SMTP conversations over an interface operating at 1000Base-T will be
slightly faster than ones over the same interfaces operating at 100Base-T, but
only under ideal conditions.
There is no point in optimizing connections to your network if there is a
bottleneck in some other part of your delivery network. Bottlenecks most
often occur in the connection to the Internet and further upstream at your
The number of Cisco IronPort appliance interfaces that you choose to connect and
how you address them should be dictated by the complexity of your underlying
network. It is not necessary to connect multiple interfaces if your network
topology or data volumes do not call for it. It is also possible to keep the
connection simple at first as you familiarize yourself with the gateway and then
increase the connectivity as volume and network topology require it.
Same Physical Interface
Different Physical Interface