The Alive Test feature specifies the method to check if a target is reachable. Options are:
- Scan Config Default (the alive test method ICMP Ping is used by default)
- ICMP Ping
- TCP-ACK Service Ping
- TCP-SYN Service Ping
- ICMP & TCP-ACK Service Ping
- ICMP & ARP Ping
- TCP-ACK Service & ARP Ping
- ICMP, TCP-ACK Service & ARP Ping
- Consider Alive
The Alive test options are discussed below:
¶ ICMP Ping
The ping command sends an ICMP echo request to a device on the network, and the device immediately responds with an ICMP echo reply. Sometimes, a company's network security policy requires ping (ICMP echo reply) to be disabled on all devices to make them more difficult to be discovered by unauthorized persons.
¶ TCP-ACK Service Ping
A TCP ACK Ping can be used to discover if a host is alive via RST response packets sent from the host. The ability to send an ACK packet to a remote host and identify the response. Creating the ACK packet without building a full connection requires the use of raw sockets.
¶ TCP-SYN Service Ping
Ping scans are used for detecting live hosts in networks. Default ping scan packets to determine if a host is responding, but if a firewall is blocking these requests, it will be treated as offline. blësk NSM supports a scanning technique named the TCP SYN ping scan that is very handy to probe different ports in an attempt to determine if a host is online or at least has more permissive filtering rules.
¶ ICMP & TCP-ACK Service Ping
In addition to an ICMP echo request to a device on the network, ARP ping function Send ARP Request, to test the reachability of IP version 4 (IPv4) systems on the local LAN by using the Address Resolution Protocol (ARP). The ARPING function sends a broadcast ARP request on a LAN to solicit a reply from the host that uses the specified IP address. If that host receives the ARP request, it sends a reply with its link-layer (or MAC) address. This reply verifies that the IP address is active and reachable on the LAN link. ARPING can test reachability only to systems on directly connected LAN links.
¶ Consider Alive
This option will allow responding to a TCP service ping with a TCP-RST even though the host is actually not alive.