昨天的一道面试题，要求找出一个网段中最长的连续可用IP，需要考虑关机的但已经静态分配了IP的机器。
当时用ping找出了能ping通的IP，但是没有想到怎么找出最长的连续段，并且不模拟多线程会比较慢。现在先不考虑关机的情况，用nmap做一遍。代码如下：
#!/bin/bash
#-----------------------------------------------------------
# Usage: 找出子网中最长连续可用ip
# $Id: continuous-ip-baidu.sh i@annhe.net 2015-08-04 12:06:11 $
#-----------------------------------------------------------
subnet="192.168.60.0/24"
used=(`nmap -sP -n $subnet |grep report |awk -F "." '{print $NF}'`)
echo "used: ${used[*]}"
num=${#used[*]}
let max=${used[1]}-${used[0]}
continuous="${used[0]} -> ${used[1]}"
for [1]i=0; i<num-1; i++; do
let next=i+1
let sum=${used[next]}-${used[i]}
if [ $sum -gt $max ]; then
max=$sum
continuous="${used[$i]} -> ${used[$next]}"
fi
done
echo -e "\n$continuous -- max:$max"结果如下：
[root@HADOOP-215 interview]# ./continuous-ip-baidu.sh
used: 1 2 129 254
2 -> 129 -- max:127参考资料
| ↑1 | i=0; i<num-1; i++ |
|---|
关机的情况 标准答案是用DNS反解。。。
试问业界有几家公司做了PTR
多谢指教
是这样查吗？[root@HADOOP-215 ~]# dig -x 216.58.221.142; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.30.rc1.el6_6.3 <<>> -x 216.58.221.142;; global options: +cmd;; Got answer:;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27880;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 4, ADDITIONAL: 4;; QUESTION SECTION:;142.221.58.216.in-addr.arpa. IN PTR;; ANSWER SECTION:142.221.58.216.in-addr.arpa. 5 IN PTR hkg07s02-in-f14.1e100.net.142.221.58.216.in-addr.arpa. 5 IN PTR hkg07s02-in-f142.1e100.net.;; AUTHORITY SECTION:221.58.216.in-addr.arpa. 5 IN NS ns3.google.com.221.58.216.in-addr.arpa. 5 IN NS ns4.google.com.221.58.216.in-addr.arpa. 5 IN NS ns1.google.com.221.58.216.in-addr.arpa. 5 IN NS ns2.google.com.;; ADDITIONAL SECTION:ns1.google.com. 5 IN A 216.239.32.10ns2.google.com. 5 IN A 216.239.34.10ns3.google.com. 5 IN A 216.239.36.10ns4.google.com. 5 IN A 216.239.38.10;; Query time: 8 msec;; SERVER: 192.168.60.2#53(192.168.60.2);; WHEN: Fri Aug 7 18:41:07 2015;; MSG SIZE rcvd: 261