BINGO!!!
it looks like a simple misconfig for DNS assigned by dhcp
# option definitions common to all supported networks...
#option domain-name "fugue.com";
#option domain-name-servers toccata.fugue.com;
option domain-name-servers 192.168.80.1;
authoritative;
in your dhcpd.conf file, change this line
option domain-name-servers 192.168.80.1;
to
option domain-name-servers <DNS IP>;
DNS IP = replace with the dns servers provided by verizon (ISP).
for example mine would be:
option domain-name-servers 71.243.0.12, 71.250.0.12;
Note that multiple servers are separated by a comma and end in a semi-colon
make that change and restart dhcp
/etc/rc.d/init.d/dhcpd restart
assuming that the core is the WAN gateway, the rest of it looks fine.
You can see that in your windows ipconfig output, the win pc is showing
DNS Servers . . . . . . . . . . . : 192.168.80.1
meaning it is looking for DNS info from the core, but the core is not acting as the DNS server.
when your client nodes ask for DNS servers from dhcp, the core is giving them 192.168.80.1 which is what is found in the line "option domain-name-servers 192.168.80.1;"
Changing that line in the dhcpd.conf file to reflect you ISP assigned DNS server IPs should do the trick.
Good Luck!!