当我执行“nmap -sT -O localhost”根据 Centos 5 部署指南，我得到：
Not shown: 1677 closed ports
PORT STATE SERVICE
22/tcp open ssh
80/tcp open http
8080/tcp open http-proxy
这很有道理。但是当我从另一台机器执行“sudo nmap -sT -O -Pn my.ip.address”时，我得到：
Not shown: 917 filtered ports
PORT STATE SERVICE
7/tcp open echo
21/tcp open ftp
22/tcp open ssh
70/tcp open gopher
83/tcp open mit-ml-dev
139/tcp closed netbios-ssn
306/tcp open unknown
366/tcp open odmr
445/tcp closed microsoft-ds
465/tcp open smtps
513/tcp open login
541/tcp open uucp-rlogin
554/tcp open rtsp
700/tcp open epp
705/tcp open agentx
901/tcp open samba-swat
992/tcp open telnets
1002/tcp open windows-icfw
1010/tcp open surf
1027/tcp open IIS
1059/tcp open nimreg
1094/tcp open rootd
1108/tcp open ratio-adp
1113/tcp open ltp-deepspace
1151/tcp open unizensus
1152/tcp open winpoplanmess
1443/tcp open ies-lm
1455/tcp open esl-lm
1494/tcp open citrix-ica
1717/tcp open fj-hdnet
1783/tcp open unknown
2323/tcp open 3d-nfsd
2394/tcp open ms-olap2
2492/tcp open groove
2557/tcp open nicetec-mgmt
2604/tcp open ospfd
2701/tcp open sms-rcinfo
3128/tcp open squid-http
3260/tcp open iscsi
3283/tcp open netassistant
3390/tcp open dsc
3766/tcp open unknown
3998/tcp open dnx
4002/tcp open mlchat-proxy
5050/tcp open mmcc
5120/tcp open unknown
5190/tcp open aol
5550/tcp open sdadmind
5631/tcp open pcanywheredata
5815/tcp open unknown
5822/tcp open unknown
5922/tcp open unknown
6692/tcp open unknown
6901/tcp open jetstream
7019/tcp open unknown
7070/tcp open realserver
7435/tcp open unknown
7938/tcp open lgtomapper
8002/tcp open teradataordbms
8010/tcp open xmpp
8085/tcp open unknown
8194/tcp open sophos
8254/tcp open unknown
8300/tcp open tmi
9002/tcp open dynamid
9594/tcp open msgsys
9929/tcp open nping-echo
10025/tcp open unknown
10243/tcp open unknown
10626/tcp open unknown
10778/tcp open unknown
12174/tcp open unknown
16012/tcp open unknown
18101/tcp open unknown
20000/tcp open dnp
20005/tcp open btx
24800/tcp open unknown
32768/tcp open filenet-tms
32777/tcp open sometimes-rpc17
32783/tcp open unknown
50001/tcp open unknown
50500/tcp open unknown
54328/tcp open unknown
啊！？最奇怪的是，防火墙不允许某些端口通过，例如 netbios-ssn，而其他端口则打开（ftp）。事实上，我的机器上甚至没有安装 ftp 服务。
我的 ipTable 如下所示：
Chain INPUT (policy DROP 531K packets, 178M bytes)
pkts bytes target prot opt in out source destination
6907 339K ACCEPT all -- lo any anywhere anywhere
115K 27M ACCEPT tcp -- any any anywhere anywhere tcp dpt:ssh
42398 45M ACCEPT all -- any any anywhere anywhere state RELATED,ESTABLISHED
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 164K packets, 30M bytes)
pkts bytes target prot opt in out source destination
更新：我真正的问题是 - 我是否可以假设，由于本地 nmap 仅显示三个服务正在监听，所以我不必担心远程 nmap 返回的所有额外条目？换句话说，是否还有其他进程正在监听而本地 nmap 未报告？
答案1
程序可以绑定到本地主机而不是外部接口，反之亦然。外部视图是更准确的视图（假设中间没有任何东西在做一些巧妙的事情）。
您可以从另一台机器连接到任何其他端口吗？
您还可以使用它lsof -i -n -P | grep LIST来查看哪些进程正在监听您机器上的端口。看看结果是否与任一nmap输出有更好的关联。