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The route command allows you to see the current routes configured on the system, as well as add and remove existing routes.
View Routes
The -n flag tells the kernel to not resolve host names, which IMHO is easier to reason with when working with IP networks.
Add a Route
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The gw <IP-of-gateway> parameter can be omitted if the route does not have a next hop gateway.
Remove a Route
When removing a route, simply use the exact same syntax used when adding the route, but change the "add" to a "del".
tcpdump
tcpdump is a stripped down version of Wireshark that allows us to view packets that are actively entering or exiting the network interfaces of a machine. There are countless tcpdump filters to get the output to show only what we're interested in. Here's a basic example that will show all ARP and ICMP packets on interface eth1. The trailing -e flag is to show Ethernet headers (MAC addresses), and the -vv is to increase the verbosity.
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