3Com 10014298 manual Enter Vlan interface, Configure the IP address for Vlan interface

70CHAPTER 4: NETWORK PROTOCOL OPERATION

Figure 19 IP Address Configuration Networking

Switch

Console cable

PC

1Enter VLAN interface 1.

[SW7750] interface vlan 1

2Configure the IP address for VLAN interface 1.

[SW7750-vlan-interface1]ip address 129.2.2.1 255.255.255.0

Troubleshooting an IP If the Ethernet Switch cannot ping a certain host on the LAN, proceed as follows:

Address Configuration

1Determine which VLAN includes the port connected to the host. Check whether the VLAN has been configured with the VLAN interface. Determine whether the IP address of the VLAN interface and the host are on the same network segment.

2If the configuration is correct, enable ARP debugging on the switch from user level, and check whether or not the switch can correctly send and receive ARP packets. If it can only send but not receive the ARP packets, there are probably errors at the Ethernet physical layer.

Configuring Address An IP address cannot be directly used for communication between network

Resolution Protocol devices, because devices can only identify MAC addresses. An IP address is the

(ARP)address of a host at the network layer. To send data packets through the network layer to the destination host, the physical address of the host is required. So the IP address must be resolved to a physical address.

When two hosts in Ethernet communicate, they must know each other’s MAC address. Every host maintains an IP-MAC address translation table, which is known as the ARP mapping table. A series of maps between IP addresses and MAC addresses of other hosts are stored in the ARP mapping table. When a dynamic ARP mapping entry is not in use for a long time, the host will remove it from the mapping table to save memory space and shorten the search interval.

Example: IP Address Resolution

Host A and Host B are on the same network segment. The IP address of Host A is IP_A and the IP address of Host B is IP_B. Host A wants to transmit packets to Host B. Host A checks its own ARP mapping table first to make sure that there are corresponding ARP entries of IP_B in the table. If the corresponding MAC address is found, Host A will use the MAC address in the ARP mapping table to encapsulate the IP packet in an Ethernet frame and send it to Host B. If the