User's Manual

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multiple subnets that connect the same physical network.
If two subnets in one network are physically separated by another network In this case, you can take the
address of the network as the subordinate IP address. Therefore, two subnets in a logical network that are
physically separated, therefore, are logically connected together.
Note:
If you configure a subordinate IP address for a routing SWITCH in a network segment, you need to do this for
other routing SWITCH in the same network segment.
Run the following command in interface configuration mode to configure multiple IP addresses on the network
interface.
Command Purpose
ip address ip-address mask secondary
Configures multiple IP addresses on the network
interface.
Note:
When the IP routing protocol is used to send the route update information, subordinate IP addresses may be
treated in different ways.
51.3.3 Configuring Address Resolution
IP can realize functions such as IP address resolution control. The following sections show how to configure
address resolution:
(1) Creating Address Resolution
An IP device may have two addresses: local address (local network segment or device uniquely identified by
LAN) and network address (representing the network where the device is located). The local address is the
address of the link layer because the local address is contained in the message header at the link layer, and
is read and used by devices at the link layer. The professionals always call it as the MAC address. This is
because the MAC sub layer in the link layer is used to process addresses.
For example, if you want your host to communicate with a device on Ethernet, you must know the 48-bit MAC
address of the device or the local address of the link layer. The process on how to obtain the local address of
the link layer from the IP address is called as Address Resolution Protocol (ARP). The process on how to
obtain the IP address from the local address of the link layer is called as Reverse Address Resolution (RARP).
Our system adopts address resolution in two types: ARP and proxy ARP. The ARP and proxy ARP are defined
in RFC 860 and 1027 respectively.
ARP is used to map IP addresses to media or MAC address. When the IP address is known, ARP will find the
corresponding MAC address. When the MAC address is known, the mapping relationship between IP address
and MAC address is saved in ARP cache for rapid access. The IP message is then packaged in the message
at the link layer and at last is sent to the network.
Defining a static ARP cache
ARP and other address resolution protocols provide a dynamic mapping between IP address and MAC address.