ARP-Ping
- 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 can check whether an IP address is being used by another device on a LAN by sending ARP packets.
The ping command is similar. However, a switching device or host may be forbidden to respond to ping packets because of a firewall. In such a case, the ping command is unable to discover whether an IP address is already in use. The ARP-Ping IP feature resolves this problem by sending ARP Request packets that are not blocked by the firewall.
ARP-Ping IP is implemented as follows:
After an IP address is specified for a device (for example, Device_A) using the arp-ping ip command, Device_A sends an ARP Request packet and starts a timer to wait for an ARP Reply packet.
If a switching device or host in the LAN detects that the destination IP address in the received ARP Request packet is the same as its own IP address, the device sends an ARP Reply packet.
Device_A performs either of the following operations depending on whether it receives an ARP Reply packet:
- An ARP Reply packet is received.
Device_A 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, Device_A displays the MAC address corresponding to the specified IP address and stops the timer. If the IP addresses are different, Device_A discards the ARP Reply packet and displays a message indicating that the IP address is idle.
- No ARP Reply packet is received before the timer expires.
Device_A displays a message indicating that the IP address is idle.
- An ARP Reply packet is received.
ARP-Ping MAC
ARP-Ping MAC can check whether a MAC address is being used by another device on a LAN by sending an ICMP Echo Request packet.
ARP-Ping MAC is implemented as follows:
After a MAC address is specified for a device (for example, Device_A) using the arp-ping mac command, Device_A sends an ICMP Echo Request packet and starts a timer to wait for an ICMP Echo Reply packet.
After receiving the ICMP Request packet, a device on the LAN replies with an ICMP Echo Reply packet.
Device_A performs either of the following operations depending on whether it receives the ICMP Echo Reply packet:
- An ICMP Echo Reply packet is received.
Device_A compares the source MAC address carried in the ICMP Echo Reply packet with the MAC address specified in the arp-ping mac command. If the two MAC addresses are the same, Device_A displays the IP address of the ICMP Echo 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 Echo Reply packets is the same as the specified MAC address, the sender discards these ICMP Echo Reply packets and displays a message indicating that the MAC address is idle.
- No ICMP Echo Reply packet is received before the timer expires.
Device_A displays a message indicating that the MAC address is idle.
- An ICMP Echo Reply packet is received.