Well this is most of the time easy but useful when need and you can't remind the command you have to use to add a static route in a Mac OS X installation.

Open fist the terminal session. Use the following command:

sudo route -n add x.x.x.x/24 x.x.x.x  

You have to enter your password.

To delete a route you have to use the following command:

sudo route -n delete x.x.x.x/24 x.x.x.x

To view you route table on you Mac you use the following command:

netstat -nr

Permanent Solution

Add a startup item (to avoid doing the above command every reboot):

cd /System/Library/StartupItems
mkdir AddRoutes
cd AddRoutes

Create a file called AddRoutes (Note: same as the folder name).

vi AddRoutes


-------------------------


#!/bin/sh
# Set static routing tables
. /etc/rc.common
StartService ()
{
if [ "${ADDROUTES:=-NO-}" = "-YES-" ]; then
ConsoleMessage "Adding Static Routing Table"
sudo route -nv add 10.0.0.0/8 10.16.3.254
fi
}
StopService ()
{
return 0
}
StopService ()
{
return 0
}
RestartService ()
{
return 0
}
RunService “$1″

Then create a file StartupParameters.plist:

{
Description = “Add static routing tables”;
Provides = (”AddRoutes”);
Requires = (”Network”);
OrderPreference = “None”;
}

Then change permissions:

chmod 755 AddRoutes StartupParameters.plist

Reboot your computer. Verify with netstat -nr.