Networking code sometimes throws UnknownHostException

This may occur if a hiccup in DNS server has occurred. Apart from making the DNS server more robust or looking for another one, you can also just use the full IP address instead of the hostname. This way it doesn't need to lookup the IP address based on the hostname. However, I would rather fix the DNS issue and prefer the DNS since IP addresses may change from time to time.

An UnknownHostException indicates the host specified couldn't be translated to an IP address. It could very well be a problem with your DNS server.