[lug] Routing with Linux

Bonnell, Doug DBonnell at BreeceHill.com
Thu Jun 29 16:12:10 MDT 2000

Forwarding is needed, but I would think that ipchaining would be
nice to use also.

I don't have the exact syntax handy, but if net1 is on Linux eth0
and net 2 is on Linux eth1, then:

     ipchain FORWARD eth1      (net1 forwarded to net2)
     ipchain FORWARD eth0      (net2 forwarded to net1)

This saves telling all the machines where packets need to go. You'll
need routing at the individual machines on each net.

     route add -host finkel -gw rupert      (finkel on net2, rupert = net1
Linux IP)

     route add -host narn -gw turtle        (narn on net1, turtle = net2
Linux IP)

First example for a machine on net1 needing to get to finkel on net2.
Second is for a machine on net2 needing to get to narn on net1.

I think of this more as a bridge than a router since it links to subnets
rather than a single connection to a subnet.

Hope this helps,
Doug Bonnell

> -----Original Message-----
> From:	Sean Reifschneider [SMTP:jafo at tummy.com]
> Sent:	Thursday, June 29, 2000 3:51 PM
> To:	lug at lug.boulder.co.us
> Subject:	Re: [lug] Routing with Linux
> On Thu, Jun 29, 2000 at 09:43:46PM +0000, Stephen G. Smith wrote:
> >Network 1 is a 35 node public static IP network
> >Network 2 is an 8 node public static IP network
> No problem.  Simply take a Linux machine with two interfaces, and plug
> one into each network.  Assign IP addresses to each interface, and
> enable packet forwarding on that machine.  It's now acting as a
> router between them.
> Now you just have to tell the 35 machines on net1 that any packets
> destined for net2 go to the IP address of the Linux machine's
> interface on their network, and the converse for the machines on
> net2.
> Or, if you have a router that's acting as your default gateway
> (connection to the internet most likely), you can tell it to
> do the forwarding so you don't have to change routing on all the
> other machines.
> Sean
> -- 
>  ISA isn't dead, it's just that people wish it were.  The correct term for
>  this condition is "legacy"...  --  Sean Reifschneider, 1999
> Sean Reifschneider, Inimitably Superfluous <jafo at tummy.com>
> tummy.com - Linux Consulting since 1995. Qmail, KRUD, Firewalls, Python
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