[CentOS] Routing issue between 2 LANs

Sun Dec 19 22:55:24 UTC 2010
Andrej Moravcik <centos at datalock.sk>

Hello Jose,

from the picture you provided the situation looks pretty simple.

- you have enabled IP forwarding on router, I recommend you to put it 
into /etc/sysctl.conf for persistence.

- you have configured firewall rules on router to allow forwarding 
traffic from left to right subnet. You can also try to set up ACCEPT 
policy just for testing.

- the default gateway for left subnet is (you mentioned 
router for Internet access). Correct me if I'm wrong.

- the default gateway for right subnet I assume is You 
don't have to do anything with routing here. Every host in right subnet 
knows where to send replies.

- the problem seems to be missing routing information in left subnet. 
Hosts don't know anything about the right subnet and thus send requests 
to the default gateway

- modifying routing table on every host in left subnet can be solution 
in case, if there is only a few hosts which need to access right subnet

- if you need to have fully accessible subnets, put the static route to 
default gateway to redirect requests to proper gateway. If 
it is Linux gateway, try something like this

[root at default-gw]# ip route add via



Jose Maria Terry Jimenez wrote:

> 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]-- 
> --------<