🚀 go-pugleaf

In <940908074839@hydra.chem.ualberta.ca>, bruce@news.srv.ualberta.ca  (Bruce Clarke) writes:
>I'm planning to make my home machine part of the office network using proxy
>arp as explained in the proposed FAQ. However, I would also like to have a
>second home machine and cannot get approval for a separate home subnet. I'm
>considering the possibility of having a private home network of two machines
>when SLIP is not running, and having the home machines function as part of
>the office net when SLIP is up. My home machines (without SLIP) would work
>
>    L1 ------------------- L2
>    home1		   home2
>
>as a private network if L2 were the default route of L1 and vice versa.

>When SLIP is up the result would be
>
>				     SLIP link
>    L1 ------------------- L2/S1-------------------S2/I1---(office net)
>    home1		   home2		  office
>
>I'm wondering if this can be made to work with proxy arp. The machines with
>two interfaces require two IP addresses, so 5 IP addresses on the office net
>would be needed.

Well, 5 addresses if you count your existing office machine's address.

I currently have this configuration set up, but I had to do "something funky" to get it to
work.  What I did was to dedicate a 14-machine subnet of our building's assigned 
254-machine subnet to SLIP-based dialups.  

I then set up the SLIP connection to home, using two addresses from within the 
reserved 14-subnet.  For the netmask parameter of the ifconfig command, I use 
"255.255.255.240".       (S1 = .253,  S2 = .254)

The home ethernet machines are set up with addresses again from the reserved 
14-subnet.  (L1 = .248,  L2 = .249)   Again, these I set up with netmasks of 
"255.255.255.240".

(This assumes the I1 machine is set up with a netmask of "255.255.255.0", yielding 
254 distinct addresses...)

On L2, I set up a proxy arp for S2.

On I1, I set up proxy arps for L1, L2, & S1.    (I'm not sure, S1 is needed here...)

Now, for routing commands beyond the defaults set up through ifconfig:

On L1 & L2:
    route add default S2 1

On I1:
   route add L1 S1 1
   route add L2 S1 1

And it works.  Note that the more restrictive netmask allows communication with all
hosts with addresses in the 14-subnet on the home-ethernet, all other addresses 
on the 254--subnet are considered default, and are routed to the office-net via SLIP.
Conversely, on the office-net, only those addresses used by proxy arp on I1 are trapped
and routed, any others can be used on the office-net.

It would probably be a good idea to employ multiple proxy arp statements on your L2
machine to account for addresses on the 14-subnet that are not used on your 
home-net.  This *should* allow for communication between your home-machines
and any other machines on the office-net with addresses in the 14-subnet range.  
This should also cover communication between two SLIP-dialup setups sharing the 
same 14-subnet address range.


>To make home1 visible to the office net, could proxy arp be used?
>Suppose the office machine executed
>
>	 arp -s S1 12:34:56:78:90:12 pub
>
>where 12:... is the MAC address of home1. Wouldn't this cause packets on the
>office network that are destined to home1 to be sent to the office machine,
>then to home2 and ultimately to home1?

Ooops!  your "arp -s ..." command should employ the MAC address of the local 
adapter, that is, your office machine instead of "home1".

On I1 you would use:

	arp -s S1 mac_address_of_I1 pub
	arp -s L2 mac_address_of_I1 pub
	arp -s L1 mac_address_of_I1 pub

On L2 you would use:

	arp -s S2 mac_address_of_L2 pub


Now for the finer points - namely how does one localize the networks when the 
SLIP modems are not connected?  That I have yet to figure out...


Don Meyer               Network Manager, 
dlmeyer@uiuc.edu       UIUC College of Agriculture Microcomputer Facility
  member:  [ NRA, IL Farm Bureau, ISSC ]

"If you line up all the Politicians in Wash. D.C. head to toe,   How much
  could you charge for tickets to drive the steamroller?' -- Clayton Cramer