No Route to Host error and solution

Q. I am getting error that read as No Route to Host. I am trying to ping my ISP gateway as well as DNS server but I am getting this error. How do I solve this problem?
A. This problem indicate networking conflicts or some sort of networking configuration problem.
Here are things to check:
a)Can you ping to your local router interface (such as 192.168.1.254)?
Make sure your card (eth0) is properly configured with correct IP address and router address. Use ifconfig command to configure IP address and route command to setup correct router address. If you prefer to use GUI tools:
redhat-config-network - Works on Red Hat and Fedora Linux/Cent OS.
network-admin - Debian and Other Linux distribution use this GUI too
Use above two GUI tools to setup correct IP address, DNS address and router address.
b) Make sure firewall is not blocking your access
iptables is default firewall on Linux. Run following command to see what iptables rules are setup:
# /sbin/iptables -L -n
You can temporary clear all iptables rules so that you can troubleshoot problem. If you are using Red Hat or Fedora Linux type command:
# /etc/init.d/iptables save
# /etc/init.d/iptables stop
If you are using other Linux distribution type following commands:
# iptables -F
# iptables -X
# iptables -t nat -F
# iptables -t nat -X
# iptables -t mangle -F
# iptables -t mangle -X
c) Finally make sure you are using a router and not a proxy server. Proxy servers are good for Internet browsing but not for other work such as ftp, sending ICMP request and so on.
See also:
List of LINUX troubleshooting commands/tools part # 1