ARP-Ping
ARP-Ping is classified as ARP-Ping IP or ARP-Ping MAC. ARP-Ping IP uses an ARP Request packet to detect whether an IP address to be configured for a device is in use. ARP-Ping MAC uses an ICMP Request packet to detect whether a MAC address to be configured for a device is in use.
ARP-Ping IP
ARP-Ping IP checks whether an IP address is used by another device on a LAN by sending an ARP packet.
Before configuring an IP address for a device, send an ARP Request packet to this IP address to check whether the IP address is in use.
The ping command can also check whether an IP address is used by other devices on the network. However, if the routing device or host that uses the IP address is enabled with the firewall function and the firewall is forbidden to respond to ping packets, the device may consider the IP address to be available. To resolve this problem, use the ARP-Ping IP feature. ARP packets are Layer 2 protocol packets and can pass through a firewall that does not respond to ping packets in most situations.
ARP-Ping IP sends ARP Request packets. ARP-Ping IP is implemented as follows:
After an IP address is specified for a device using the arp-ping ip command, the device sends an ARP Request packet and starts a timer to wait for an ARP Reply packet.
If the routing device or host in the LAN detects that the destination IP address in the received ARP Request packet is the same as the local IP address, the device or host sends an ARP Reply packet.
The sender performs either of the following operations depending on whether the ARP Reply packet is received:
- If the sender receives an ARP Reply packet, the sender compares the source IP address carried in the ARP Reply packet with the IP address specified in the arp-ping ip command. If the two IP addresses are the same, the MAC address corresponding to the specified IP address is displayed on the sender and the timer stops. If the IP addresses are different, the sender discards the ARP Reply packet and displays a message indicating that the IP address is idle.
- If the ARP Reply packet times out, the sender displays a message indicating that the IP address is idle.
ARP-Ping MAC
ARP-Ping MAC checks whether a MAC address is used by another device on a LAN by sending an ICMP Request (Echo Request) packet.
ARP-Ping MAC is implemented as follows:
After a MAC address is specified for a device using the arp-ping mac command, the device sends an ICMP Request packet and starts a timer to wait for an ICMP Reply packet.
After receiving the ICMP Request packet, the device on the LAN replies with an ICMP Reply (Echo Reply) packet.
The sender performs either of the following operations depending on whether the ICMP Reply packet is received:
- If the sender receives an ICMP Reply packet, the sender compares the source MAC address carried in the ICMP Reply packet with the MAC address specified in the arp-ping mac command. If the two MAC addresses are the same, the sender displays the source IP address of the ICMP Reply packet and displays a message indicating that the MAC address is in use, and the timer stops. If no source MAC addresses carried in the received ICMP Reply packets is the same as the specified MAC address, the sender discards these ICMP Reply packets and displays a message indicating that the MAC address is idle.
- If the ICMP Reply packet times out, the sender displays a message indicating that the MAC address is idle.