ネットワーク内にあるサーバのIPアドレスが分からなくなった場合の調査

nmapを使うと比較的簡単に実施できます．
Ping scanningなので結果もすぐに表示されます．

$ nmap -sP 192.168.0.0/24

Starting nmap 3.70 ( http://www.insecure.org/nmap/ ) at 2008-06-04 10:47 JST
Host web02 (192.168.0.2) appears to be up.
Host web10 (192.168.0.10) appears to be up.
Host 192.168.0.23 appears to be up.
Host web55 (192.168.0.55) appears to be up.
Host 192.168.0.88 appears to be up.
Nmap run completed -- 256 IP addresses (5 hosts up) scanned in 2.457 seconds

これで起動しているIPを突いてみれば分かります．

時間がかかってもサービスまで知りたい時は下記で

$ nmap -sT 192.168.0.0/24

Starting nmap 3.70 ( http://www.insecure.org/nmap/ ) at 2008-06-04 16:53 JST
Interesting ports on web10 (192.168.0.10):
(The 1656 ports scanned but not shown below are in state: filtered)
PORT STATE SERVICE
21/tcp open ftp
25/tcp open smtp
80/tcp open http
3306/tcp closed mysql

-- 省略 --
Nmap run completed -- 256 IP addresses (1 hosts up) scanned in 1657.082 seconds