squid and dns

Hello, I have installed last year some servers with suse 6.4 and squid. They works fine with no need of more actions. But then, some weeks ago I noticed some problems on the dns-servers of the provider. They are now solved, but since then, my proxy-boxes works not in the way I known it? Very often they told me they could not resolve the adresses. After I cleared the cache and restart the proxy-server, the box works fine for one week. But now, I have the same problem very often they could not resolve the adresses. Have anyone an idea? Thomas