Summary - How to turn on IP forwarding on a Sun 3/260 SunOS 4.1

Date: Mon Jul 29 1991 - 20:57:49 CDT

  Many thanks to everyone who replied. Two approaches were suggested,
patching the kernal with adb and making a new kernal. I chose the latter,
added "option IPFORWARDING" to the config file, and rebuilt it. Looking
at the code, ip_forwarding defaults to off, not on, as some people
suggested, at least in OS 4.1. Here's the way to do it with adb:

You have to adb the kernel to toggle the value. Be warned that Sun changed
the name of the variable in 4.1 -- it now has an underscore in its name:

        leibniz# adb -k -w /vmunix /dev/mem
        physmem ff3
        ip_forwarding/D # display the value of ip_forwarding
         _ip_forwarding: # found the variable
        _ip_forwarding: 0 # it's currently turned off
        ./W 1 # toggle the value to on
        _ip_forwarding: 0x0 = 0x1 # okay, it's on
        .?W 1 # toggle it on in the disk version
        _ip_forwarding: 0x0 = 0x1 # okay, it's on too

       $q # quit

You type the "ip_forwarding/D", "./W 1", and ".?W 1". The others lines are
the output from adb. The slash refers to items in the core file, /dev/mem,
and the question mark refers to items in the object file, /vmunix. If you
don't change the core file, your changes will go away on the next boot.
[- Jim Duncan]


To those who asked if I really needed to do this, I do. I have a Mac and a GatorBox on the Ethernet side and NEARNet on the other side. They meet in the Sun.

Also, it was suggested that I used gated rather than routed. I'm currently running with routed but will probably change that when I get a chance.

Again, thanks to everyone who helped out! (There were about 20 people with correct answers.)


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