Squid 2.7 & sync outside time server

[jose perez <jopeme2000@xxxxxxxx>]

Hello.
I run a squid proxy server 2.7 and several pcs access to internet through it on 
a network environment.
My windows xp clients cannot time sync to the outside world (time.nist.gov , 
time-a.nist.gov). It is using 3128 port and internet navigation is right.

How i can solve this?

Thanks.