dns配置文件的俩个疑问

Question

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我看了dns配置，有疑问如下：
1.竟然域名是uc88.domain，那么在uc88.domain配置文件里为什么多了一个st（如@ IN SOA st.uc88.domain. root.st.uc88.domain. ），这个st代表什么意思，是不是可以随便在uc88.domain文件里的@ IN SOA st.uc88.domain. root.st.uc88.domain.这一句可以用任意多个字符代替st？
2.uc88.domain文件里的www，ftp，mail是主机名？
www IN A 192.168.25.15
ftp IN A 192.168.25.15
mail IN A 192.168.25.15

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  以下是摘录的配置文件：
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

我们知道dns是域名服务，提供ip和域名转换的服务。这样我们就不用记很长的ip 地址 而可以使用好记的名称来代替如 我的http://www.uc88.domain来访问/ 我的网页，mail.uc88,domain来访问邮件服务，ftp.uc88.domain来访问我的ftp服务器了~！
相关配置文件有以下几个：
192.168.25.rev
named.conf
resolv.conf
uc88.domain

详细配置如下：
192.168.25.rev

$TTL 86400
@ IN SOA st.uc88.domain. root.st.uc88.domain. (
2001111601 ; Serial
28800 ; Refresh
14400 ; Retry
3600000 ; Expire
86400 ) ; Minimum
@ IN NS st.uc88.domain.
@ IN MX 10 mail.uc88.domain.
15 IN PTR st.uc88.domain.

named.conf

// generated by named-bootconf.pl

options {
directory "/var/named";
/*
* If there is a firewall between you and nameservers you want
* to talk to, you might need to uncomment the query-source
* directive below. Previous versions of BIND always asked
* questions using port 53, but BIND 8.1 uses an unprivileged
* port by default.
*/
// query-source address * port 53;
};

//
// a caching only nameserver config
//
controls {
inet 127.0.0.1 allow { localhost; } keys { rndckey; };
};
zone "." IN {
type hint;
file "named.ca";
};

zone "localhost" IN {
type master;
file "localhost.zone";
allow-update { none; };
};

zone "0.0.127.in-addr.arpa" IN {
type master;
file "named.local";
allow-update { none; };
};

zone "uc88.domain" IN {
type master;
file "uc88.domain";
allow-update { none; };
};

zone "25.168.192.in-addr.arpa" IN {
type master;
file "192.168.25.rev";
allow-update { none; };
};

include "/etc/rndc.key";

resolv.conf

nameserver 192.168.25.15
nameserver 202.96.128.68

uc88.domain
$TTL 86400
@ IN SOA st.uc88.domain. root.st.uc88.domain. (
2001111601 ; Serial
28800 ; Refresh
14400 ; Retry
3600000 ; Expire
86400 ) ; Minimum

@ IN NS st.uc88.domain.
@ IN MX 10 mail.uc88.domain.

localhost IN A 127.0.0.1
www IN A 192.168.25.15
ftp IN A 192.168.25.15
mail IN A 192.168.25.15