[H-GEN] Routing

[Craig Eldershaw]

(Note reply-to: being general at humbug.org.au vs Craig Eldershaw <ce at comlab.ox.ac.uk>)

>I'm wanting to know the best way to route a dial-up connection onto the
>local ethernet.
>
>We have an ethernet of IP's 10.10.10.0/255.255.255.0
>
>What IP should I use on the dial-in at each end?  

<snip>

>>unless you have real IP's (ie. not private network ones) then what you
>>are
>>trying to do is quite impossible cause the return packets will not know
>>where to route to.
>
>That's why there's a router on each private subnet.  I'm going to set
                                ^^^^^^^^^^^^^^^^^^^
>the routing rules so that they both know where the other subnet is.


OK, if I have this straight from the last response: we are connecting
two *private* networks (over both of which we have complete control)
and there is no external link (to machines with real IPs)

In that case, simply have the first subnet as 10.10.10.0/255.255.255.0
and the second as 10.10.11.0/255.255.255.0 .  Then there is no need to
use ARP or any such thing (which is only needed in dynamic situations,
or machines with bootroms).  Just fix the two ends at 10.10.10.1 and
10.10.11.1 .  Then you have nice simple routing rules like:

route add -net 10.10.10.0 netmask 255.255.255.0 eth0
route add -net 10.10.11.0 netmask 255.255.255.0 gw 10.10.10.1

at the 10.10.10 side (and the converse on the 10.10.11 side) for all
the non-router hosts.  For the router host, set ppp0 to be 10.10.12.10
(10.10.12.11 for the other end) and add the rules:

route add -net 10.10.10.0 netmask 255.255.255.0 eth0
route add -host 10.10.12.11 netmask 255.255.255.255 ppp0
route add -net 10.10.11.0 netmask 255.255.255.0 gw 10.10.12.11

with the obvious converse on the other router.

>If I pick a number in
>the 10.10.10. range wouldn't that be routed already as on the ethernet?
>How can I route the connection so that the dialin modem will be visible
>to the network, and vice-versa?  

The above rules tell any machine on the 10.10.10 subnet that they can
get to all their collegues via ethernet, but if they want to get to a
machine on the other subnet, then to send their packets to the router
machine.  It in turn knows that to get to the other subnet, it chucks it
at the modem, the other router takes care of it from there.

Now any machine can access any other on either subnet using the
10.10.1[10].* address.  No arp or masq required.

Or am I missing something in the original question ?

C.

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