clockdiff: fixup help info

If neither '-o' nor '-o1' option avaliable, using ICMP Timestamp. run_state::ip_opt_len field controls IP or ICMP timestamp method is used.
Mingli-Yu · Jan 9, 2020 · 5f5f23f · 5f5f23f
1 parent 2308234
commit 5f5f23f
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/clockdiff.c b/clockdiff.c
@@ -451,7 +451,7 @@ static void usage(int exit_status)
 		"\nUsage:\n"
 		"  clockdiff [options] <destination>\n"
 		"\nOptions:\n"
-		"                without -o, use ip timestamp only\n"
+		"                without -o, use icmp timestamp only(see RFC0792, page 16)\n"
 		"  -o            use ip timestamp and icmp echo\n"
 		"  -o1           use three-term ip timestamp and icmp echo\n"
 		"  -T, --time-format <ctime|iso>\n"