dns and subdomain

[gliu]

Hi
As a newbee in setting Dns server,I have a few questions in learining.

The  Administrator of my company have give me a subdomain to be accesseb from internet.I was response for setting the domain server.

go.nu -->the domain of my company 210.220.18.2

b.go.nu-->the domain name of my department 210.220.3.100

Now I tried to set up a linux server just for test.

dns server name -->b.go.nu ip-->192.168.2.3
I found there was no problem at solving machine in 192.168.2.0/24.(ping hostname<->ping ip).It was impossible to ping outside.eg: ping ip (of yahoo) Ok,but ping www.yahoo.com error.

Here are my setting files.
zone "." {
    type hint;
    file "named.cache"; downloaded  from ftp://internic.net and copied to /var/named/
};
zone "go.nu ip"{
    type master;
    file "db.s.b.nu"
};

file db.s.nu

@  SOA b.s.go.nu. root at s.b.nu. (
    1997022700 ; Serial 
    28800 ; Refresh 
    14400 ; Retry 
    3600000 ; Expire 
    86400 ; Minimum 
)
NS b.s.go.nu.
b IN A 192.168.2.7
test IN A 192.168.2.5

file /etc/

My questions are

1. How can not I ping nameserver at internet although i setup the root.cache.Is it for the local ip address? Can I do it if I use the true internet address(210.220.3.100)?

2. Do I have to use the localhost and 0.0.127.in-addr.arpa as two zones. System knows localhost and 127.0.0.1 each others in default.

3. As using "master" type ,how can the dns server  refresh its database by the time ( 
    1997022700 ; Serial 
    28800 ; Refresh 
    14400 ; Retry 
    3600000 ; Expire 
    86400 ; Minimum )

Thanks in advance!