计划

2015年计划

随感

孤独2

怎么样追踪网络状态

2015年06月21日

[目录]

访问过程

访问域名：

访问 www.baidu.com => dns 服务器解析 ip => 访问目标服务器指定端口 => 接收结果

访问ip:

访问目标服务器指定端口 => 接收结果

关键点

相比直接访问ip的服务（更简单的可以认为是一个客户端，比如游戏），访问域名多了一层域名转换为ip的操作，这里就涉及到了dns服务器。

dns 服务器

当想要了解dns服务器的使用情况，就可以用dig或者nslookup。

dig 命令

	dig www.baidu.com
	
	result:
	
	; <<>> DiG 9.8.3-P1 <<>> www.baidu.com
	;; global options: +cmd
	;; Got answer:
	;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17928
	;; flags: qr; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

	;; QUESTION SECTION:
	;www.baidu.com.			IN	A

	;; ANSWER SECTION:
	www.baidu.com.		90	IN	A	115.239.210.27

	;; Query time: 7 msec
	;; SERVER: 192.168.0.1#53(192.168.0.1)
	;; WHEN: Sun Jun 21 18:07:21 2015
	;; MSG SIZE  rcvd: 47

nslookup 命令

	nslookup www.baidu.com

	result:
	
	Server:		192.168.0.1
	Address:	192.168.0.1#53

	Non-authoritative answer:
	Name:	www.baidu.com
	Address: 115.239.210.27

nslookup 和 dig 的区别

dig uses the OS resolver libraries. nslookup uses is own internal ones.

That is why ISC has been trying to get people to stop using nslookup for some time now. It causes confusion.

具体区别：链接

ip 路由

traceroute 命令

	traceroute www.baidu.com
	
	result:

	traceroute to www.baidu.com (115.239.211.112), 64 hops max, 52 byte packets
	 1  broadcom.home (192.168.1.1)  3.711 ms  20.582 ms  2.439 ms
	 2  1.244.79.218.broad.xw.sh.dynamic.163data.com.cn (218.79.244.1)  5.666 ms  11.499 ms  4.777 ms
	 3  1.244.79.218.broad.xw.sh.dynamic.163data.com.cn (218.79.244.1)  5.553 ms  5.073 ms  6.881 ms
	 4  124.74.12.169 (124.74.12.169)  10.230 ms  4.781 ms  7.916 ms
	 5  124.74.215.225 (124.74.215.225)  4.984 ms  5.607 ms  4.250 ms
	 6  61.152.86.6 (61.152.86.6)  8.878 ms
	    61.152.86.2 (61.152.86.2)  6.869 ms
	    101.95.120.74 (101.95.120.74)  7.159 ms
	 7  202.97.68.42 (202.97.68.42)  8.499 ms
	    202.97.68.130 (202.97.68.130)  8.605 ms
	    202.97.68.142 (202.97.68.142)  9.064 ms
	 8  61.164.31.178 (61.164.31.178)  7.207 ms  8.641 ms
	    61.164.13.150 (61.164.13.150)  22.457 ms
	 9  115.233.23.202 (115.233.23.202)  9.513 ms  10.111 ms
	    115.233.23.194 (115.233.23.194)  7.215 ms
	10  115.239.209.10 (115.239.209.10)  10.664 ms  10.027 ms
	    115.239.209.26 (115.239.209.26)  9.850 ms
	11  *

网络延时

ping 命令

	ping www.baidu.com

	result:
	
	PING www.baidu.com (115.239.211.112): 56 data bytes
	64 bytes from 115.239.211.112: icmp_seq=0 ttl=53 time=11.615 ms
	64 bytes from 115.239.211.112: icmp_seq=1 ttl=53 time=17.961 ms
	64 bytes from 115.239.211.112: icmp_seq=2 ttl=53 time=8.919 ms

合理的ping值

一般而言，150ms 之下的ping值都是可以接受的，一旦到了200ms之上，可能路由器或则modem有问题了（当然，外部网络堵塞的原因这里不多说）。

There are two normal factors that significantly influence the latency of a consumer device (like a cable modem, dsl modem or dial-up modem).

  1. The latency of the connecting device. For a cable modem, this can normally be between 5 and 40 ms. For a DSL modem this is normally 10 to 70ms. For a dial-up modem, this is normally anywhere from 100 to 220ms. For a cellular link, this can be from 200 to 600 ms. For a T1, this is normally 0 to 10 ms.
  2. The distance the data is traveling. Data travels at (very roughly) 120,000 miles (or 192,000 kilometers) per second, or 120 miles (192 km) per ms (millisecond) over a network connection. With traceroute, we have to send the data there and back again, so roughly 1 ms of latency is added for every 60 miles (96km, although with the level of accuracy we’re using here, we should say ‘100km’) of distance between you and the target.

查看原文：链接

其他

服务可访问性

服务的概念

port & socket & service

简而言之

  1. port 是网卡的虚拟识别号，用于区分网络链接。
  2. socket 是ip 和 port 的绑定
  3. app 如果绑定到 sockect ，就可以提供service

telnet 命令

telnet 用于检查某ip的某端口是否对测试者开放，便是服务的可访问性。当然，在软件层面，还可以对访问者要求权限认证，但这是另外一个话题。

	telnet 115.239.211.112 80
	
	result:
	
	Trying 115.239.211.112...
	Connected to 115.239.211.112.
	Escape character is '^]'.