LINUX networking problems

hi,

i wish to ask regarding the LINUX networking setting:

actually i am new user to LINUX and currently take the short course regarding the liNUX-RedHat, so i was trying to setting up my new server Compaq Prosignia 500.

I faced below below when i try to setting the newtorking:

1)actually we have another dns running in my company already which called dns1.duraco.com.sg
i named the practice PC as dns3.duraco.com.sg
when i use the pratice pc to ping the dns1.duraco.com.sg which have 203.126.241.50 IP address but it seems stoped and didn't show anything.
but when i try to ping to my ISP, i can ping out and the got respond from the ISP.

I just curious why i can't ping to my dns1.duraco.com.sg , is it because both server at thesame company, then i can't ping ?

i try to ping to my dns1.duraco.com.sg when i studying the LINUX course at computer lab , from outsiders ping to my dns1.duraco.com.sg.

may i know why and how can i able to ping to 203.126.241.50 because when i put the name server as 203.126.241.50 and use the command nslookup, it also seems no responding as well

please assists because i am stuck there already.

please help

hoay fern