Diagnose Network Problems

1. PING.
#ping host

Try to ping the host. Ping shows RTT. RTT means how close a host is to you.
Ping also shows if the connection is unreliable. E.g. 50% packet loss.
ping works on ICMP.

#ping -f -i 1 host


#ping -f -c 500 -s 1400 host (Flood ping (dont use it))

2. TRACEROUTE
#tracerote host

Sometimes, ICMP, or UDP are not open on remote server. Then use below:
#traceroute -T (this uses TCP and not UDP)

3. MTR
Instead of above two, use MTR. It is a network diagnostic tool. And MTR = traceroute + ping.
It also shows you jitter, ie inconsistency in response time. In other words its the congestion in network.
Press j or d during mtr.

#mtr

Alternatively, use following tools. It gives more info than traceroute like firewalls, gateways, routers etc.
#lft
#conky on host
#gkrellm
#netstat
#iftop -nNPB
#iptraf