我在使用CentOS 6.2安装的新盒子上遇到了一些DNS问题.
我可以使用nslookup,dig或host查找名称.我能够通过名称或IP地址ping机器.但是,当我尝试其他工具(如ssh,wget或yum)时,它们无法解析名称.例如：
# wget http://www.google.com --2012-03-08 14:48:06-- http://www.google.com/ Resolving www.google.com... Failed: Name or service not known. wget: unable to resolve host address `www.google.com' # ssh www.google.com ssh: Could not resolve hostname www.google.com: Name or service not known # ping -c 1 www.google.com PING www.l.google.com (74.125.113.106) 56(84) bytes of data. 64 bytes from vw-in-f106.1e100.net (74.125.113.106): icmp_seq=1 ttl=46 time=43.6 ms --- www.l.google.com ping statistics --- 1 packets transmitted,1 received,0% packet loss,time 59ms rtt min/avg/max/mdev = 43.665/43.665/43.665/0.000 ms # host www.google.com www.google.com is an alias for www.l.google.com. www.l.google.com has address 74.125.113.99 www.l.google.com has address 74.125.113.103 www.l.google.com has address 74.125.113.104 www.l.google.com has address 74.125.113.105 www.l.google.com has address 74.125.113.106 www.l.google.com has address 74.125.113.147
我的/etc/nsswitch.conf文件是默认文件,包括这个(标准)行：
hosts: files dns
/etc/resolv.conf是由DHCP设置的：
; generated by /sbin/dhclient-script nameserver 192.168.1.254
192.168.1.254是一个有效的DNS服务器(我的DSL调制解调器,与其他机器一起工作多年)
任何人都知道为什么ping会工作,但ssh / wget会失败？
根据NcA的建议,我尝试将/etc/resolv.conf更改为指向8.8.8.8.奇怪的是,这确实有效.显然,我的DSL调制解调器以某种方式响应DNS请求,而Linux的解析系统的某些部分并不喜欢.看看tcpdump,我无法看出它有什么区别.当然,两台服务器都发送相同的地址.
这是tcpdump -nn -X的输出,服务器设置为DSL调制解调器上的DNS服务器.它显然是用正确的地址回复的,但是由于某种原因,ssh / wget似乎并不满意：
15:53:52.133580 IP 192.168.1.254.53 > 192.168.1.2.54836: 33157 7/0/0 CNAME www.l.google.com.,A 74.125.115.105,A 74.125.115.106,A 74.125.115.147,A 74.125.115.99,A 74.125.115.103,A 74.125.115.104 (148)
0x0000: 4500 00b0 e33a 0000 ff11 53b1 c0a8 01fe E....:....S.....
0x0010: c0a8 0102 0035 d634 009c 7528 8185 8180 .....5.4..u(....
0x0020: 0001 0007 0000 0000 0377 7777 0667 6f6f .........www.goo
0x0030: 676c 6503 636f 6d00 0001 0001 c00c 0005 gle.com.........
0x0040: 0001 0007 acd0 0008 0377 7777 016c c010 .........www.l..
0x0050: c02c 0001 0001 0000 0001 0004 4a7d 7369 .,..........J}si
0x0060: c02c 0001 0001 0000 0001 0004 4a7d 736a .,..........J}sj
0x0070: c02c 0001 0001 0000 0001 0004 4a7d 7393 .,..........J}s.
0x0080: c02c 0001 0001 0000 0001 0004 4a7d 7363 .,..........J}sc
0x0090: c02c 0001 0001 0000 0001 0004 4a7d 7367 .,..........J}sg
0x00a0: c02c 0001 0001 0000 0001 0004 4a7d 7368 .,..........J}sh
15:53:52.135669 IP 192.168.1.254.53 > 192.168.1.2.54836: 65062- 0/0/0 (32)
0x0000: 4500 003c e33b 0000 ff11 5424 c0a8 01fe E..<.;....T$....
0x0010: c0a8 0102 0035 d634 0028 98f9 fe26 8000 .....5.4.(...&..
0x0020: 0001 0000 0000 0000 0377 7777 0667 6f6f .........www.goo
0x0030: 676c 6503 636f 6d00 001c 0001 gle.com.....
我不是一个专家知道这是否在某种程度上是畸形的,但ping似乎是正确的做法.
为了比较,在查询8.8.8.8时这是同样的事情：
15:57:27.990270 IP 8.8.8.8.53 > 192.168.1.2.49028: 59114 7/0/0 CNAME www.l.google.com.,A 74.125.113.105,A 74.125.113.103,A 74.125.113.106,A 74.125.113.147,A 74.125.113.104,A 74.125.113.99 (148)
0x0000: 4500 00b0 5530 0000 2f11 6453 0808 0808 E...U0../.dS....
0x0010: c0a8 0102 0035 bf84 009c 39f8 e6ea 8180 .....5....9.....
0x0020: 0001 0007 0000 0000 0377 7777 0667 6f6f .........www.goo
0x0030: 676c 6503 636f 6d00 0001 0001 c00c 0005 gle.com.........
0x0040: 0001 0001 516a 0008 0377 7777 016c c010 ....Qj...www.l..
0x0050: c02c 0001 0001 0000 0116 0004 4a7d 7169 .,..........J}qi
0x0060: c02c 0001 0001 0000 0116 0004 4a7d 7167 .,..........J}qg
0x0070: c02c 0001 0001 0000 0116 0004 4a7d 716a .,..........J}qj
0x0080: c02c 0001 0001 0000 0116 0004 4a7d 7193 .,..........J}q.
0x0090: c02c 0001 0001 0000 0116 0004 4a7d 7168 .,..........J}qh
0x00a0: c02c 0001 0001 0000 0116 0004 4a7d 7163 .,..........J}qc
15:57:28.018909 IP 8.8.8.8.53 > 192.168.1.2.49028: 31984 1/1/0 CNAME www.l.google.com. (102)
0x0000: 4500 0082 7b1b 0000 2f11 3e96 0808 0808 E...{.../.>.....
0x0010: c0a8 0102 0035 bf84 006e c67e 7cf0 8180 .....5...n.~|...
0x0020: 0001 0001 0001 0000 0377 7777 0667 6f6f .........www.goo
0x0030: 676c 6503 636f 6d00 001c 0001 c00c 0005 gle.com.........
0x0040: 0001 0001 517f 0008 0377 7777 016c c010 ....Q....www.l..
0x0050: c030 0006 0001 0000 0258 0026 036e 7334 .0.......X.&.ns4
0x0060: c010 0964 6e73 2d61 646d 696e c010 0016 ...dns-admin....
0x0070: 91f3 0000 0384 0000 0384 0000 0708 0000 ................
0x0080: 003c .<
我仍然不知道为什么服务器的回复适用于ping而不适用于ssh / wget.
如果有人有想法,我会很高兴听到他们的意见.但是现在,我可以引用外部DNS服务器或在新机器上设置我自己的服务器.这是一个似乎应该没有必要的解决方法,但允许我继续.
