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Instead of hard-coding in a check to scrape info from ifconfig based on a specific interface, do it in a more portable way.
This works really well if you switch between wired, wireless, bluetooth or even VPN connections. You can get your current IP in a script (since it'll be something like tun0 instead of eth0 or wlan1).
This uses a well known public ip address 8.8.8.8, but it doesn't actually connect to it, it just shows you the route it would take.
Useful to determine the source_ip of outgoing packages to a certain destination
Can be used in a firewall script, e.g. to avoid logging broadcast packtes.
Find your default gateway and print it directly output
http://www.bilgisayarmatematik.com/
kerim@bayner.com
ip address show | grep eth0 | sed '1d' | awk '{print $2}'
does the same, but shows network-prefix.
Someone might attack on your system. You can drop attacker IP using IPtables. However, you can use route command to null route unwanted traffic. A null route (also called as blackhole route) is a network route or kernel routing table entry that goes nowhere. Matching packets are dropped (ignored) rather than forwarded, acting as a kind of very limited firewall. The act of using null routes is often called blackhole filtering.