new option --check-source

Using the new option --check-source discards Echo reply packets
sourced from an address that is different from the specified target
address.  This can be useful on busy monitoring hosts, because it
is possible that two fping processes running at he same time use
the same ICMP Echo Reply Identifier for ICMP Echo messages sent to
different hosts.

This aims to address GH issue #206.

ci/test-02-help.pl

@@ -1,6 +1,6 @@
 #!/usr/bin/perl -w
 
-use Test::Command tests => 12;
+use Test::Command tests => 15;
 
 my $I_HELP = "   -I, --iface=IFACE  bind to a particular interface\n";
 $I_HELP = '' if $^O eq 'darwin';
@@ -38,3 +38,9 @@
 $cmd3->exit_is_num(1);
 $cmd3->stdout_is_eq("");
 $cmd3->stderr_like(qr{^fping: (illegal|invalid) option -- '?Z'?\nsee 'fping -h' for usage information\n$});
+
+# fping with unknown long option
+my $cmd5 = Test::Command->new(cmd => "fping --unknown-long-option");
+$cmd5->exit_is_num(1);
+$cmd5->stdout_is_eq("");
+$cmd5->stderr_like(qr{^fping: (illegal|invalid) option -- '?unknown-long-option'?\nsee 'fping -h' for usage information\n$});

ci/test-05-options-c-e.pl

@@ -1,11 +1,13 @@
 #!/usr/bin/perl -w
 
-use Test::Command tests => 51;
+use Test::Command tests => 63;
+use Test::More;
 
-#  -c n       count of pings to send to each target (default 1)
-#  -C n       same as -c, report results in verbose format
-#  -D         print timestamp before each output line
-#  -e         show elapsed time on return packets
+#  -c n           count of pings to send to each target (default 1)
+#  -C n           same as -c, report results in verbose format
+#  --check-source discard replies not from target address
+#  -D             print timestamp before each output line
+#  -e             show elapsed time on return packets
 
 # fping -c n
 {
@@ -126,6 +128,57 @@
 });
 }
 
+# fping --check-source
+{
+my $cmd = Test::Command->new(cmd => "fping --check-source 127.0.0.1 127.0.0.2");
+$cmd->exit_is_num(0);
+$cmd->stdout_is_eq("127.0.0.1 is alive\n127.0.0.2 is alive\n");
+$cmd->stderr_is_eq("");
+}
+
+# fping --check-source (to IPv6 multicast address -> accept no reply)
+SKIP: {
+    if($ENV{SKIP_IPV6}) {
+        skip 'Skip IPv6 tests', 3;
+    }
+    my $cmd = Test::Command->new(cmd => "fping --check-source ff02::1");
+    $cmd->exit_is_num(1);
+    $cmd->stdout_is_eq("ff02::1 is unreachable\n");
+    $cmd->stderr_is_eq("");
+}
+
+# fping -c N --check-source
+SKIP: {
+    if($ENV{SKIP_IPV6}) {
+        skip 'Skip IPv6 tests', 3;
+    }
+    my $cmd = Test::Command->new(cmd => "fping -c1 --check-source 127.0.0.1 ff02::1");
+    $cmd->exit_is_num(1);
+    $cmd->stdout_like(qr{127\.0\.0\.1 : \[0\], 64 bytes, \d\.\d+ ms \(\d\.\d+ avg, 0% loss\)
+ff02::1   : \[0\], timed out \(NaN avg, 100% loss\)
+});
+    $cmd->stderr_like(qr{
+127\.0\.0\.1 : xmt/rcv/%loss = 1/1/0%, min/avg/max = \d\.\d+/\d\.\d+/\d\.\d+
+ff02::1   : xmt/rcv/%loss = 1/0/100%
+});
+}
+
+# fping -C N --check-source
+SKIP: {
+    if($ENV{SKIP_IPV6}) {
+        skip 'Skip IPv6 tests', 3;
+    }
+    my $cmd = Test::Command->new(cmd => "fping -C1 --check-source 127.0.0.1 ff02::1");
+    $cmd->exit_is_num(1);
+    $cmd->stdout_like(qr{127\.0\.0\.1 : \[0\], 64 bytes, \d\.\d+ ms \(\d\.\d+ avg, 0% loss\)
+ff02::1   : \[0\], timed out \(NaN avg, 100% loss\)
+});
+    $cmd->stderr_like(qr{
+127\.0\.0\.1 : \d\.\d+
+ff02::1   : -
+});
+}
+
 # fping -D
 {
 my $cmd = Test::Command->new(cmd => "fping -D -c 2 -p 100 127.0.0.1");

doc/fping.pod

@@ -81,6 +81,13 @@ shows the response time in milliseconds for each of the five requests, with the
 C<-> indicating that no response was received to the fourth request.  This
 option overrides B<-a> or B<-u>.
 
+=item B<--check-source>
+
+Discard Echo replies that are sourced from a different address than the target
+address. This avoids spurious reachability results on busy monitoring systems
+where two B<fping> instances with the same lower 16 bits of the process ID may
+be running at the same time.
+
 =item B<-d>, B<--rdns>
 
 Use DNS to lookup address of ping target. This allows you to give fping

src/fping.c

@@ -360,6 +360,7 @@ int timestamp_flag = 0;
 int timestamp_format_flag = 0;
 int random_data_flag = 0;
 int cumulative_stats_flag = 0;
+int check_source_flag = 0;
 #if defined(DEBUG) || defined(_DEBUG)
 int randomly_lose_flag, trace_flag, print_per_system_flag;
 int lose_factor;
@@ -556,6 +557,7 @@ int main(int argc, char **argv)
         { "version", 'v', OPTPARSE_NONE },
         { "reachable", 'x', OPTPARSE_REQUIRED },
         { "fast-reachable", 'X', OPTPARSE_REQUIRED },
+        { "check-source", '0', OPTPARSE_NONE },
 #if defined(DEBUG) || defined(_DEBUG)
         { NULL, 'z', OPTPARSE_REQUIRED },
 #endif
@@ -576,6 +578,10 @@ int main(int argc, char **argv)
               }else{
                 usage(1);
               }
+            } else if (strstr(optparse_state.optlongname, "check-source") != NULL) {
+                check_source_flag = 1;
+            } else {
+                usage(1);
             }
             break;
         case '4':
@@ -2436,6 +2442,12 @@ int wait_for_reply(int64_t wait_time)
 
     dbg_printf("received [%d] from %s\n", this_count, h->host);
 
+    /* optionally require reply source equal to target address */
+    if (check_source_flag && addr_cmp((struct sockaddr *)&response_addr, (struct sockaddr *)&h->saddr)) {
+        dbg_printf("discarding reply from wrong source address\n");
+        return 1;
+    }
+
     /* discard duplicates */
     if (!loop_flag && h->resp_times[this_count] >= 0) {
         if (!per_recv_flag) {
@@ -3037,6 +3049,7 @@ void usage(int is_error)
     fprintf(out, "   -S, --src=IP       set source address\n");
     fprintf(out, "   -t, --timeout=MSEC individual target initial timeout (default: %.0f ms,\n", timeout / 1e6);
     fprintf(out, "                      except with -l/-c/-C, where it's the -p period up to 2000 ms)\n");
+    fprintf(out, "       --check-source discard replies not from target address\n");
     fprintf(out, "\n");
     fprintf(out, "Output options:\n");
     fprintf(out, "   -a, --alive        show targets that are alive\n");