IP-forwarding (help)

[Bakul Shah]

On 05 Jun 2008 01:33:05 +0200 "Arno J. Klaassen" <arno at heho.snv.jussieu.fr>  wrote:
> Petar Bogdanovic <petar at smokva.net> writes:
> 
> > On Wed, Jun 04, 2008 at 11:06:01PM +0200, Arno J. Klaassen wrote:
> > > 
> > > Hello,
> > > 
> > > this is probably a FAQ and/or I'm to tired, but I'd be pleased
> > > if anyone can tell me what I do wrong :
> > > 
> > > I have a box with two interfaces, one connected to my lan
> > > (172.16. ), one to a test-box (192.168.1.1) :
> > > 
> > >   em0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 15
> 00
> > >         options=9b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
> > >         ether xxx
> > >         inet 172.16.1.240 netmask 0xffffff00 broadcast 172.16.1.255
> > >         media: Ethernet autoselect (1000baseTX <full-duplex>)
> > >         status: active
> > > 
> > >   em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 15
> 00
> > >         options=9b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM>
> > >         ether xxx
> > >         inet 192.168.1.254 netmask 0xffffff00 broadcast 192.168.1.255
> > >         media: Ethernet autoselect (1000baseTX <full-duplex>)
> > >         status: active
> > > 
> > > 
> > > I enable ip.forwarding :
> > > 
> > >   # sysctl net.inet.ip.forwarding
> > >   net.inet.ip.forwarding: 1
> > > 
> > > 
> > > And this is my routing table :
> > > 
> > >  Internet:
> > >  Destination        Gateway            Flags    Refs      Use  Netif Expi
> re
> > >  default            172.16.1.254       UGS         0       20    em0
> > >  127.0.0.1          127.0.0.1          UH          0        0    lo0
> > >  172.16.1.0/24      link#3             UC          0        0    em0
> > >  172.16.1.6         xxxxxxxxxxxxxxxxx  UHLW        1       87    em0   11
> 94
> > >  172.16.1.230       xxxxxxxxxxxxxxxxx  UHLW        1      286    em0    5
> 72
> > >  172.16.1.240       xxxxxxxxxxxxxxxxx  UHLW        1        0    lo0
> > >  172.16.1.254       xxxxxxxxxxxxxxxxx  UHLW        2        0    em0    4
> 87
> > >  192.168.1.0/24     link#4             UC          0        0    em1
> > >  192.168.1.1        xxxxxxxxxxxxxxxxx  UHLW        1        2    em1    6
> 16
> > >  192.168.1.254      xxxxxxxxxxxxxxxxx  UHLW        1        0    lo0
> > > 
> > > For this I added to rc.conf :
> > > 
> > >   static_routes="test lan"
> > >   route_test="-net 192.168.1.0/24 192.168.1.254" 
> > >   route_lan="-net 172.16.1.0/24 172.16.1.240"
> > 
> > I'm pretty sure that you don't need these three lines. Turning
> > net.inet.ip.forwarding on should be enough.

> I feel this is /me still not fully understand routing tables. 

This is your topology, right?

   test-box                   main-box                   gateway
[192.168.1.1]------[192.168.1.254 172.16.1.240]-------[172.16.1.254

On the test-box set default route to 192.168.1.254.
On the main-box set net.inet.ip.forwarding 1 but remove the
static routes.

But how would machines on the 172.16.1.0/24 net know they
must send packets for 192.168.1.0/24 to 172.16.1.240?  For
that you need static routes on all the machines on
172.16.1.0/24 that need to read your test box.