bind NS TTL设置问题

[yjh625]

环境：
OS：redhat 5.3 64bit
BIND：9.9.2 release

现在情况是这样的我有两个域名：myeasou.cn及shift.myeasou.cn，我现在需要修改shift.myeasou.cn的TTL时间，刚开始直接在myeaosu.cn的配置文档设置shift.myeasou.com，但是不生效；后来直接修改了shift.easou.com NS记录TTL时间，这样就生效了。可是这样就让我们困惑，NS TTL的时间不是以上级域名的设置为主吗？如果是本级域名为主的话，那我myeaosu.cn设置TTL为10分钟为什么不生效。觉得这个很怪，请大神帮忙解答下。具体配置信息如下：

myeasou.com:

$TTL 6000
@ IN SOA admin.myeasou.cn. ns3.myeasou.cn. (
2012102604 ; Serial
28800 ; Refresh
14400 ; Retry
3600000 ; Expire
86400 ) ; Minimum
IN NS ns3.myeasou.cn.
IN NS ns4.myeasou.cn.
shift.myeasou.cn. IN NS ns1.shift.myeasou.cn.
shift.myeasou.cn. IN NS ns2.shift.myeasou.cn.
ns3 IN A 120.197.95.234
ns4 IN A 120.197.95.235
ns1.shift IN A 120.197.95.234
ns2.shift IN A 120.197.95.235


shift.myeasou.com:

$TTL 600
@ IN SOA admin.shift.myeasou.cn. ns3.shift.myeasou.cn. (
2012102600 ; Serial
28800 ; Refresh
14400 ; Retry
3600000 ; Expire
86400 ) ; Minimum
86400 IN NS ns1.shift.myeasou.cn.
86400 IN NS ns2.shift.myeasou.cn.
ns1 IN A 120.197.95.234
ns2 IN A 120.197.95.235


NS trace信息如下：

[root@szmlvm29-78 named]# dig ns1.shift.myeasou.cn +trace

; <<>> DiG 9.3.4-P1 <<>> ns1.shift.myeasou.cn +trace
;; global options: printcmd
. 288575 IN NS c.root-servers.net.
. 288575 IN NS k.root-servers.net.
. 288575 IN NS b.root-servers.net.
. 288575 IN NS l.root-servers.net.
. 288575 IN NS a.root-servers.net.
. 288575 IN NS f.root-servers.net.
. 288575 IN NS m.root-servers.net.
. 288575 IN NS g.root-servers.net.
. 288575 IN NS i.root-servers.net.
. 288575 IN NS e.root-servers.net.
. 288575 IN NS j.root-servers.net.
. 288575 IN NS h.root-servers.net.
. 288575 IN NS d.root-servers.net.
;; Received 512 bytes from 120.197.95.235#53(120.197.95.235) in 1 ms

cn. 172800 IN NS a.dns.cn.
cn. 172800 IN NS c.dns.cn.
cn. 172800 IN NS d.dns.cn.
cn. 172800 IN NS b.dns.cn.
cn. 172800 IN NS ns.cernet.net.
cn. 172800 IN NS e.dns.cn.
;; Received 301 bytes from 192.33.4.12#53(c.root-servers.net) in 207 ms

myeasou.cn. 21600 IN NS ns4.myeasou.cn.
myeasou.cn. 21600 IN NS ns3.myeasou.cn.
;; Received 106 bytes from 203.119.25.1#53(a.dns.cn) in 37 ms

ns1.shift.myeasou.cn. 600 IN A 120.197.95.234
shift.myeasou.cn. 86400 IN NS ns1.shift.myeasou.cn.
shift.myeasou.cn. 86400 IN NS ns2.shift.myeasou.cn.
;; Received 102 bytes from 120.197.95.235#53(ns4.myeasou.cn) in 0 ms