[squid-users] problem : DNS timed out in SQUID

Dear All,
  I have problem with SQUID-2.5STABLE9-7 in Fedora Core 4, sometimes
browser in our client display "unable to determined IP Address from
host name for www.google.co.id ", dnsserver returned " Timeout" but
when i try to resolve using dig tools in SQUID proxy itself, the
machine can resolve the query.
  Problem can be solved by restarting squid service. I install squid
using RPM on P4-3 Ghz, 512 MHz.
Here is my squid.conf
http_port 8080
cache_dir ufs /var/spool/squid 1000 16 256
dns_nameservers 202.127.97.18 202.127.18.19
refresh_pattern ^ftp: 1440 20% 10080
refresh_pattern ^gopher: 1440 0% 1440
refresh_pattern . 0 20% 4320
acl all src 0.0.0.0/0.0.0.0
acl manager proto cache_object
acl localhost src 127.0.0.1/255.255.255.255
acl net1 src 10.100.0.0/255.255.0.0
acl net2 src 10.150.0.0/255.255.0.0
acl net3 src 10.10.0.0/255.255.0.0
acl to_localhost dst 127.0.0.0/8
acl SSL_ports port 443 563
acl Safe_ports port 80 # http
acl Safe_ports port 21 # ftp
acl Safe_ports port 443 563 # https, snews
acl Safe_ports port 70 # gopher
acl Safe_ports port 210 # wais
acl Safe_ports port 1025-65535 # unregistered ports
acl Safe_ports port 280 # http-mgmt
acl Safe_ports port 488 # gss-http
acl Safe_ports port 591 # filemaker
acl Safe_ports port 777 # multiling http
acl CONNECT method CONNECT
http_access allow manager localhost
http_access allow localhost
http_access deny manager
http_access deny !Safe_ports
http_access deny CONNECT !SSL_ports
http_access allow net1
http_access allow net2
http_access allow net3
http_access allow localhost
http_access deny all
http_reply_access allow all
icp_access allow all
visible_hostname xxx.xx.xx

my vmstat when dns error's displayed
# vmstat
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
 r b swpd free buff cache si so bi bo in cs us sy id wa
 1 0 844 6148 17920 387332 0 0 4 49 44 48 3 1 96 0
Received on Mon Nov 19 2007 - 02:10:15 MST