3Com 3032 Configuration Manual page 161

Sub-Interface
Configure Sub-Interface
Any packet reaching the null interface will be dropped, which provides another
method for packet filtering: Just sending unnecessary network traffic to Null0
interface, so that there is no need to configure ACL.
For example: Use static routing configuration command
192.101.0.0 255.255.0.0 null 0
segment 192.101.0.0.
2 Configure operating parameters of the interface
is the only command which can be configured on the Null
ip unreachables
interface. It indicates that the router will reply the ICMP unreachable packet when
it receives packets sent to the Null interface.
Please perform the following configurations in Null interface view.
Table 189 Configure/Remove the sending of ICMP unreachable packet
Operation
Configure the sending of ICMP unreachable packet
Remove the sending of ICMP unreachable packet
The 3Com Router comes up with the concept of "sub-interface" and allows users
to configure multiple sub-interfaces on one physical interfaces on the 3Com
Router series, making it very flexible for configuration.
Sub-interfaces refer to the multiple logical virtual interfaces configured on one
physical interface. These virtual interfaces share the physical layer parameters of
the physical interface, meanwhile, they can be configured with their own link layer
parameters and network layer parameters. Therefore, the multiple virtual
interfaces corresponding to one physical are called "sub-interfaces".
In the 3Com Router series, the physical interfaces supporting sub-interface
features include:
Ethernet interface: When the sub-interface of Ethernet has not been
configured with VLAN id, the sub-interface can only support IPX network
protocol. After configured with VLAN id, it will be able to support both IPX and
IP protocols.
WAN interface which link layer protocol is frame relay: Its sub-interface can
support IP and IPX network protocols.
WAN interface which link layer protocol is X.25: Its sub-interface can support IP
and IPX network protocols.
According to different physical interfaces, sub-interface configuration includes:
Configure sub-interfaces of Ethernet interface
Configure sub-interfaces of WAN interface which link layer protocol is frame
relay
Configure sub-interfaces of WAN interface which link layer protocol is X.25
ip route-static
will drop all the packets sent to network
Command
ip unreachables
undo ip unreachables
Sub-Interface 157