3Com 4007, Implementation Manual, Page: 360 / 684

360 C
HAPTER
16: IP R
OUTING
If you define multiple interfaces for an IP VLAN, you cannot subsequently
modify that IP VLAN to supply Layer 3 address information. If only one
routing interface is defined for the IP VLAN, then you can supply Layer 3
address information as long as it matches the Layer 3 information
specified for the routing interface. This latter procedure is not
recommended, since it makes the IP VLAN a network-based VLAN.
If you continue to use network-based VLANs for this release, you are
limited to defining only
one IP routing interface for that VLAN. When you
define an IP routing interface for a static VLAN already configured, the
module will not allow you to select a network-based IP VLAN that already
has a routing interface defined for it.
Media Access Control
(MAC) Address
The MAC address refers to a physical hardware address. On a LAN, the
MAC address is the unique hardware number of your device. The MAC
address on an Ethernet LAN is the same as your Ethernet address.
Network-Layer
Address
The network-layer address refers to a logical address that applies to a
specific protocol. A network-layer address exists at Layer 3 of the
OSI reference model.
IP Addresses IP addresses are 32-bit addresses that consist of a network part (the
address of the network where the host is located) and a host part (the
address of the host on that network).
Figure 33 IP Address: Network Part and Host Part
IP addresses differ from Ethernet and Fiber Distributed Data Interface
(FDDI) MAC addresses, which are unique hardware-configured 48-bit
addresses. A central agency assigns the network part of the IP address,
and you assign the host part. All devices that are connected to the same
network share the same network part (also called the
prefix ).
IP Address
network host
32 bits
The boundary between network
and host parts depends on the
class of IP network.