linux – 5秒解析延迟

使用wget(curl,httplib2)我总是得到5秒的解析超时.当我做wget -4或wget -6时,这个问题没有到来.解决方案也可以使用挖掘或主机.使用/etc/resolv.conf中的“options timeout：2”可以降低延迟

这个strace输出是：

15:19:09.908234 uname({sys="Linux",node="openkvk",...}) = 0 
15:19:09.908413 socket(PF_INET,SOCK_DGRAM|SOCK_NONBLOCK,IPPROTO_IP) = 3 
15:19:09.908482 connect(3,{sa_family=AF_INET,sin_port=htons(53),sin_addr=inet_addr("212.83.206.202")},16) = 0 
15:19:09.908569 poll([{fd=3,events=POLLOUT}],1,0) = 1 ([{fd=3,revents=POLLOUT}]) 
15:19:09.908637 sendto(3,"F\347\1\0\0\1\0\0\0\0\0\0\10slashdot\3org\0\0\1\0\1",30,MSG_NOSIGNAL,NULL,0) = 30 
15:19:09.908735 poll([{fd=3,events=POLLIN|POLLOUT}],5000) = 1 ([{fd=3,revents=POLLOUT}])
15:19:09.908804 sendto(3,"F\331\1\0\0\1\0\0\0\0\0\0\10slashdot\3org\0\0\34\0\1",0) = 30 
15:19:09.908884 poll([{fd=3,events=POLLIN}],4999) = 1 ([{fd=3,revents=POLLIN}]) 
15:19:09.911230 ioctl(3,FIONREAD,[46]) = 0 
15:19:09.911308 recvfrom(3,"F\347\201\200\0\1\0\1\0\0\0\0\10slashdot\3org\0\0\1\0\1\300\f"...,2048,[16]) = 46 
15:19:09.911445 poll([{fd=3,4997) = 0 (Timeout) 
15:19:14.909096 poll([{fd=3,revents=POLLOUT}]) 
15:19:14.909189 sendto(3,0) = 30 
15:19:14.909292 poll([{fd=3,revents=POLLIN}]) 
15:19:14.911569 ioctl(3,[46]) = 0 
15:19:14.911644 recvfrom(3,[16]) = 46 
15:19:14.911772 poll([{fd=3,4997) = 1 ([{fd=3,revents=POLLOUT}]) 
15:19:14.911837 sendto(3,0) = 30 
15:19:14.912051 poll([{fd=3,revents=POLLIN}]) 
15:19:14.914034 ioctl(3,[106]) = 0

Tcpdump输出：

tcpdump -vvv  port 53 
tcpdump: listening on eth0,link-type EN10MB (Ethernet),capture size 65535 bytes 
15:19:09.908687 IP (tos 0x0,ttl 64,id 37830,offset 0,flags [DF],proto UDP (17),length 58) 
    93.157.136.242.38551 > 212.83.206.202.domain: [bad udp cksum 3576!] 18151+ A? slashdot.org. (30) 
15:19:09.908852 IP (tos 0x0,id 37831,length 58) 
    93.157.136.242.38551 > 212.83.206.202.domain: [bad udp cksum 2876!] 18137+ AAAA? slashdot.org. (30) 
15:19:09.911081 IP (tos 0x0,ttl 59,id 0,length 74) 
    212.83.206.202.domain > 93.157.136.242.38551: [udp sum ok] 18151 q: A? slashdot.org. 1/0/0 slashdot.org. [22m21s] A 216.34.181.45 (46) 
15:19:14.909246 IP (tos 0x0,id 37832,length 58) 
    93.157.136.242.38551 > 212.83.206.202.domain: [bad udp cksum 3576!] 18151+ A? slashdot.org. (30) 
15:19:14.911442 IP (tos 0x0,length 74) 
    212.83.206.202.domain > 93.157.136.242.38551: [udp sum ok] 18151 q: A? slashdot.org. 1/0/0 slashdot.org. [22m16s] A 216.34.181.45 (46) 
15:19:14.911882 IP (tos 0x0,id 37833,length 58) 
    93.157.136.242.38551 > 212.83.206.202.domain: [bad udp cksum 2876!] 18137+ AAAA? slashdot.org. (30) 
15:19:14.913906 IP (tos 0x0,length 134) 
    212.83.206.202.domain > 93.157.136.242.38551: [udp sum ok] 18137 q: AAAA? slashdot.org. 0/1/0 ns: slashdot.org. [3m39s] SOA ns-1.ch3.sourceforge.com. hostmaster.corp.sourceforge.com. 2011101300 14400 1800 604800 3600 (106)

像dig / host这样的工具执行类似于使用wget -4或wget -6,即时,没有任何问题.

我已经分别尝试了以下每个服务器.

nameserver 2001:4018:3:12::202
nameserver 2001:4018:1:64::202
nameserver 212.83.206.202
nameserver 213.207.64.202
nameserver 8.8.8.8
nameserver 8.8.4.4

什么可能导致这种延迟？

请求的输出：
wget -4(作品)

23:41:10.428217 IP (tos 0x0,id 11790,length 55)
    93.157.136.242.51379 > 212.83.206.202.domain: [bad udp cksum e070!] 65414+ A? vircon.nl. (27)
23:41:10.430442 IP (tos 0x0,length 71)
    212.83.206.202.domain > 93.157.136.242.51379: [udp sum ok] 65414 q: A? vircon.nl. 1/0/0 vircon.nl. [15h59m29s] A 31.193.104.52 (43)

23:41:10.427920 socket(PF_INET,IPPROTO_IP) = 3
23:41:10.427982 connect(3,16) = 0
23:41:10.428095 poll([{fd=3,revents=POLLOUT}])
23:41:10.428166 sendto(3,"\377\206\1\0\0\1\0\0\0\0\0\0\6vircon\2nl\0\0\1\0\1",27,0) = 27
23:41:10.428262 poll([{fd=3,revents=POLLIN}])
23:41:10.430572 ioctl(3,[43]) = 0
23:41:10.430651 recvfrom(3,"\377\206\201\200\0\1\0\1\0\0\0\0\6vircon\2nl\0\0\1\0\1\300\f\0\1\0"...,1024,[16]) = 43
23:41:10.430774 close(3)

wget(破碎)

23:40:13.577621 IP (tos 0x0,id 20475,length 55)
    93.157.136.242.55276 > 212.83.206.202.domain: [bad udp cksum 16c!] 62764+ A? vircon.nl. (27)
23:40:13.577786 IP (tos 0x0,id 20476,length 55)
    93.157.136.242.55276 > 212.83.206.202.domain: [bad udp cksum 9654!] 61847+ AAAA? vircon.nl. (27)
23:40:13.579879 IP (tos 0x0,length 71)
    212.83.206.202.domain > 93.157.136.242.55276: [udp sum ok] 62764 q: A? vircon.nl. 1/0/0 vircon.nl. [22h20m8s] A 31.193.104.52 (43)
23:40:18.582490 IP (tos 0x0,id 20477,length 55)
    93.157.136.242.55276 > 212.83.206.202.domain: [bad udp cksum 16c!] 62764+ A? vircon.nl. (27)
23:40:18.584709 IP (tos 0x0,length 71)
    212.83.206.202.domain > 93.157.136.242.55276: [udp sum ok] 62764 q: A? vircon.nl. 1/0/0 vircon.nl. [16h21s] A 31.193.104.52 (43)
23:40:18.585163 IP (tos 0x0,id 20478,length 55)
    93.157.136.242.55276 > 212.83.206.202.domain: [bad udp cksum 9654!] 61847+ AAAA? vircon.nl. (27)
23:40:18.587212 IP (tos 0x0,length 106)
    212.83.206.202.domain > 93.157.136.242.55276: [udp sum ok] 61847 q: AAAA? vircon.nl. 0/1/0 ns: vircon.nl. [56m25s] SOA ns1.vircon.nl. hostmaster.vircon.nl. 2011120602 10800 3600 604800 86400 (78)

23:40:13.577353 socket(PF_INET,IPPROTO_IP) = 3
23:40:13.577417 connect(3,16) = 0
23:40:13.577502 poll([{fd=3,revents=POLLOUT}])
23:40:13.577572 sendto(3,"\365,\1\0\0\1\0\0\0\0\0\0\6vircon\2nl\0\0\1\0\1",0) = 27
23:40:13.577667 poll([{fd=3,revents=POLLOUT}])
23:40:13.577737 sendto(3,"\361\227\1\0\0\1\0\0\0\0\0\0\6vircon\2nl\0\0\34\0\1",0) = 27
23:40:13.577892 poll([{fd=3,revents=POLLIN}])
23:40:13.580007 ioctl(3,[43]) = 0
23:40:13.580105 recvfrom(3,\201\200\0\1\0\1\0\0\0\0\6vircon\2nl\0\0\1\0\1\300\f\0\1\0"...,[16]) = 43
23:40:13.580229 poll([{fd=3,4997) = 0 (Timeout)
23:40:18.582338 poll([{fd=3,revents=POLLOUT}])
23:40:18.582433 sendto(3,0) = 27
23:40:18.582535 poll([{fd=3,revents=POLLIN}])
23:40:18.584835 ioctl(3,[43]) = 0
23:40:18.584912 recvfrom(3,[16]) = 43
23:40:18.585048 poll([{fd=3,revents=POLLOUT}])
23:40:18.585117 sendto(3,0) = 27
23:40:18.585300 poll([{fd=3,revents=POLLIN}])
23:40:18.587325 ioctl(3,[78]) = 0
23:40:18.587394 recvfrom(3,"\361\227\201\200\0\1\0\0\0\1\0\0\6vircon\2nl\0\0\34\0\1\300\f\0\6\0"...,2005,[16]) = 78
23:40:18.587513 close(3)

解决方法

您的问题在 http://udrepper.livejournal.com/20948.html中描述,并且由IPv4和IPv6上的并行查找引起,该查找与某些DNS服务器和防火墙不兼容.

可以通过在/etc/resolv.conf中的选项中添加“single-request”来修复它,如上面提到的链接.