[CentOS] Routing issue between 2 LANs

Sun Dec 19 18:01:39 UTC 2010
Les Mikesell <lesmikesell at gmail.com>

On 12/19/10 11:07 AM, Jose Maria Terry Jimenez wrote:
> Hello All
> First, sorry by my poor english, hope you understand me :-)
> I have a problem, i don't understand or don't know how to solve
> I need to interconnect 2 networks with different numbers. One is
> the other Mainly i need to access services in
> the 236. from the 1. one.
> I have a CentOS 5.5 machine with 2 nics each one configured to work in one of
> the nets. The CentOS also uses a router for Internet access that is
> >-----[CentOS Machine]-- --------<
> So, i enable forwarding in the CentOS box
> echo '1' > /proc/sys/net/ipv4/ip_forward
> And in one machine of the 1. network (this is Fedora14) I add the route:
> route add -net netmask gw dev eth0
> Since this moment i can ping or access (ssh/http) another CentOS machine in the
> 236 network
> ping
> PING ( 56(84) bytes of data.
> 64 bytes from icmp_req=1 ttl=64 time=0.281 ms
> But can't access or ping other machines (NOT Linux ones), ie, printers, Win
> servers, etc...
> Also tried adding:
> route add eth0
> before the route add -net, but no efect.
> This fails even if i flush IPTables.
> In the CentOS box that replies, i did nothing, it 'just' works.
> Can anyone tell what is happening / help me with this?
> Something to do missing in the CentOS router that joins the networks?

First make sure that you can ping/access those 'other' services from the centos 
box with 2 nics.   It should source from the .236 interface and 'just work'.  If 
not, you have firewalls or something else blocking traffic.   When you route 
other traffic from the .1 network, the destination machines need some reason to 
send the return packets to the address.  You can either add the 
route to every machine or on the router that is currently their default router.

   Les Mikesell
      lesmikesell at gmail.com