Your external (what you posted) looks fine.
Is the only IP assigned to the box 170.211.174.36? or do you have a private ip?-for which you need the machine to resolve lookups from the local dns (the bind articles or use the 2 dns boxes you already have) and get a private ip, usually like the below:
10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255
(assigned via dchp or manually set on every computer)
/blog/archives/2007/06/making_zimbra_bind_work_together_1.html