[NTLUG:Discuss] iptables / router problem

[Chris Cox]

kbrannen at gte.net wrote:
...snip...
> ###
> iptables --flush
> iptables --table nat --flush
> iptables --delete-chain
> iptables --table nat --delete-chain
> 
> # Set up IP FORWARDing and Masquerading
> iptables --table nat --append POSTROUTING --out-interface eth0 -j 
> MASQUERADE
> iptables --append FORWARD --in-interface eth1 -j ACCEPT
> 
> # Enables packet forwarding by kernel
> echo 1 > /proc/sys/net/ipv4/ip_forward
> 
> # Create a route for internal packets
> route add  -net 192.168.1.0  netmask 255.255.255.0 gw 172.16.0.1 dev eth1
> ###

If you've got IP forwarding enabled and both interfaces are local... it
already knows how to move packets from one net to the other.  Local
hosts will use your 192.168.1.1 as their default gateway.

> 
> All of which looks reasonable, and all seems to work until I get to the 
> route command at the end.  That fails with a "SIOCADDRT: Network is 
> unreachable".
> 
> A "route -n" gives:
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref    Use 
> Iface
> 192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 
> eth1
> 172.16.0.0      0.0.0.0         255.255.252.0   U     0      0        0 
> eth0
> 0.0.0.0         172.16.0.1      0.0.0.0         UG    0      0        0 
> eth0
> 
> A ifconfig gives:
> eth0      Link encap:Ethernet  HWaddr 00:40:F6:B8:BA:6E
>           inet addr:172.16.1.247  Bcast:172.16.3.255  Mask:255.255.252.0
...snip...
> 
> eth1      Link encap:Ethernet  HWaddr 00:40:F6:14:18:2C
>           inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
...snip...
> 
> plus a "lo" entry.  This all looks good too.
> 
> Can anyone offer any suggestions?
> 
> TIA!!!
> Kevin