| Test for a host being reachable using ICMP "ping" packets & echo operations.
Ping packets are very reliable for assessing reachability in a LAN or WAN,
but they do not get through any well-configured firewall. Echo (port 7) may.
This condition turns unknown host exceptions into false conditions. This is
because on a laptop, DNS is one of the first services lost when the network
goes; you are implicitly offline.
If a URL is supplied instead of a host, the hostname is extracted and used in
the test--all other parts of the URL are discarded.
The test may not work through firewalls; that is, something may be reachable
using a protocol such as HTTP, while the lower level ICMP packets get dropped
on the floor. Similarly, a host may be detected as reachable with ICMP, but not
reachable on other ports (i.e. port 80), because of firewalls.
Requires Java1.5+ to work properly. On Java1.4 and earlier, if a hostname
can be resolved, the destination is assumed to be reachable.
since:
Ant 1.7 |
