Cisco Cisco Email Security Appliance C170 Guia Do Utilizador
B-2
Cisco IronPort AsyncOS 7.6 for Email Configuration Guide
OL-25136-01
Appendix B Assigning Network and IP Addresses
An IP address identifies a physical interface on any given network. A physical Ethernet interface can
have more than one IP address for which it accepts packets. An Ethernet interface that has more than one
IP address can send packets over that interface with any one of the IP addresses as the source address in
the packet. This property is used in implementing Virtual Gateway technology.
have more than one IP address for which it accepts packets. An Ethernet interface that has more than one
IP address can send packets over that interface with any one of the IP addresses as the source address in
the packet. This property is used in implementing Virtual Gateway technology.
The purpose of a netmask is to divide an IP address into a network address and a host address. The
network address can be thought of as the network part (the bits matching the netmask) of the IP address.
The host address is the remaining bits of the IP address. The number of bits in a four octet address that
are significant are sometimes expressed in CIDR (Classless Inter-Domain Routing) style. This is a slash
followed by the number of bits (1-32).
network address can be thought of as the network part (the bits matching the netmask) of the IP address.
The host address is the remaining bits of the IP address. The number of bits in a four octet address that
are significant are sometimes expressed in CIDR (Classless Inter-Domain Routing) style. This is a slash
followed by the number of bits (1-32).
A netmask can be expressed in this way by simply counting the ones in binary, so
255.255.255.0
becomes “
/24
” and
255.255.240.0
becomes “
/20
”.
Sample Interface Configurations
This section shows sample interface configurations based on some typical networks. The example will
use two interfaces called Int1 and Int2. In the case of the Cisco IronPort appliance, these interface names
can represent any two interfaces out of the three Cisco IronPort interfaces (Management, Data1, Data2).
use two interfaces called Int1 and Int2. In the case of the Cisco IronPort appliance, these interface names
can represent any two interfaces out of the three Cisco IronPort interfaces (Management, Data1, Data2).
Network 1:
Separate interfaces must appear to be on separate networks.
Data addressed to
192.168.1.X
(where X is any number 1-255, except for your own address, 10 in this
case) will go out on Int1. Anything addressed to
192.168.0.X
will go out on Int2. Any packet headed
for some other address not in these formats, most likely out on a WAN or the Internet, will be sent to the
default gateway which must itself be on one of these networks. The default gateway will then forward
the packet on.
default gateway which must itself be on one of these networks. The default gateway will then forward
the packet on.
Network 2:
The network addresses (network parts of the IP addresses) of two different interfaces cannot be the same.
This situation presents a conflict in that two different Ethernet interfaces have the same network address.
If a packet from the Cisco IronPort appliance is sent to
If a packet from the Cisco IronPort appliance is sent to
192.168.1.11
, there is no way to decide which
Ethernet interface should be used to deliver the packet. If the two Ethernet interfaces are connected to
two separate physical networks, the packet may be delivered to the incorrect network and never find its
destination. The Cisco IronPort appliance will not allow you to configure your network with conflicts.
two separate physical networks, the packet may be delivered to the incorrect network and never find its
destination. The Cisco IronPort appliance will not allow you to configure your network with conflicts.
You can connect two Ethernet interfaces to the same physical network, but you must construct IP
addresses and netmasks to allow the Cisco IronPort appliance to select a unique delivery interface.
addresses and netmasks to allow the Cisco IronPort appliance to select a unique delivery interface.
Interface
IP address
netmask
net address
Int1
192.168.1.10
255.255.255.0
192.168.1.0/24
Int2
192.168.0.10
255.255.255.0
192.168.0.0/24
Ethernet Interface
IP address
netmask
net address
Int1
192.168.1.10
255.255.0.0
192.168.0.0/16
Int2
192.168.0.10
255.255.0.0
192.168.0.0/16