Messages sent using UDP user server port 53 (decimal).
Messages carried by UDP are restricted to 512 bytes (not counting the IP
or UDP headers). Longer messages are truncated and the TC bit is set in
the header.
UDP is not acceptable for zone transfers, but is the recommended method
for standard queries in the Internet. Queries sent using UDP may be
lost, and hence a retransmission strategy is required. Queries or their
responses may be reordered by the network, or by processing in name
servers, so resolvers should not depend on them being returned in order.
The optimal UDP retransmission policy will vary with performance of the
Internet and the needs of the client,...........................作者: yxx608 时间: 2010-07-19 17:40
dig @202.102.224.68 www.taobao.com
;; AUTHORITY SECTION:
gslb.taobao.com. 6006 IN NS gslbns2.taobao.com.
gslb.taobao.com. 6006 IN NS gslbns1.taobao.com.
gslb.taobao.com. 6006 IN NS gslbns3.taobao.com.
;; ADDITIONAL SECTION:
gslbns1.taobao.com. 341 IN A 121.0.23.218
gslbns2.taobao.com. 3966 IN A 115.124.17.70
gslbns3.taobao.com. 4028 IN A 110.75.3.193
; <<>> DiG 9.5.2-P4 <<>> www.taobao.com +trace
;; global options: printcmd
. 403579 IN NS g.root-servers.net.
. 403579 IN NS f.root-servers.net.
. 403579 IN NS b.root-servers.net.
. 403579 IN NS j.root-servers.net.
. 403579 IN NS h.root-servers.net.
. 403579 IN NS c.root-servers.net.
. 403579 IN NS d.root-servers.net.
. 403579 IN NS m.root-servers.net.
. 403579 IN NS a.root-servers.net.
. 403579 IN NS l.root-servers.net.
. 403579 IN NS k.root-servers.net.
. 403579 IN NS i.root-servers.net.
. 403579 IN NS e.root-servers.net.
;; Received 512 bytes from 202.98.96.68#53(202.98.96.6 in 421 ms
com. 172800 IN NS i.gtld-servers.net.
com. 172800 IN NS e.gtld-servers.net.
com. 172800 IN NS b.gtld-servers.net.
com. 172800 IN NS m.gtld-servers.net.
com. 172800 IN NS a.gtld-servers.net.
com. 172800 IN NS h.gtld-servers.net.
com. 172800 IN NS f.gtld-servers.net.
com. 172800 IN NS c.gtld-servers.net.
com. 172800 IN NS l.gtld-servers.net.
com. 172800 IN NS j.gtld-servers.net.
com. 172800 IN NS k.gtld-servers.net.
com. 172800 IN NS d.gtld-servers.net.
com. 172800 IN NS g.gtld-servers.net.
;; Received 492 bytes from 192.228.79.201#53(b.root-servers.net) in 328 m
taobao.com. 172800 IN NS ns1.taobao.com.
taobao.com. 172800 IN NS ns2.taobao.com.
taobao.com. 172800 IN NS ns3.taobao.com.
;; Received 134 bytes from 192.26.92.30#53(c.gtld-servers.net) in 281 ms
www.taobao.com. 1800 IN CNAME www.gslb.taobao.com. gslb.taobao.com. 86400 IN NS gslbns3.taobao.com. gslb.taobao.com. 86400 IN NS gslbns1.taobao.com. gslb.taobao.com. 86400 IN NS gslbns2.taobao.com.
;; Received 169 bytes from 121.0.23.188#53(ns3.taobao.com) in 93 ms
淘宝在DNS前面加了防DDOS设备,当DNS请求达到阈值,会回DNS tc置位报文,而将UDP改为TCP,进而使用 safe re ...
panmeng2000 发表于 2010-08-02 11:59