CentOS - Dec 2010 - Routing issue between 2 LANs

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
192.168.236.0/24 the other 192.168.1.0/24. 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 192.168.1.1.

192.168.1.0/24 >-----192.168.1.100--[CentOS Machine]--192.168.236.74
--------< 192.168.236.0/24

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 192.168.236.0 netmask 255.255.255.0 gw 192.168.1.100 dev eth0

Since this moment i can ping or access (ssh/http) another CentOS machine in the
236 network
ping 192.168.236.74
PING 192.168.236.74 (192.168.236.74) 56(84) bytes of data.
64 bytes from 192.168.236.74: 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 192.168.1.100 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? 

Best,
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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
> 192.168.236.0/24 the other 192.168.1.0/24. 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
192.168.1.1.
>
> 192.168.1.0/24 >-----192.168.1.100--[CentOS Machine]--192.168.236.74
--------<
> 192.168.236.0/24
>
> 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 192.168.236.0 netmask 255.255.255.0 gw 192.168.1.100 dev
eth0
>
> Since this moment i can ping or access (ssh/http) another CentOS machine in
the
> 236 network
> ping 192.168.236.74
> PING 192.168.236.74 (192.168.236.74) 56(84) bytes of data.
> 64 bytes from 192.168.236.74: 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 192.168.1.100 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 192.168.236.74 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

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 192.168.1.1 (you mentioned 
router for Internet access). Correct me if I'm wrong.

- the default gateway for right subnet I assume is 192.168.236.74. 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 192.168.1.1.

- 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 192.168.1.1 to redirect requests to proper gateway. If 
it is Linux gateway, try something like this

[root at default-gw]# ip route add 192.168.236.0/24 via 192.168.236.74


Regards

Andrej



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 192.168.1.1.
> 
> 192.168.1.0/24 >-----192.168.1.100--[CentOS Machine]--192.168.236.74 
> --------< 192.168.236.0/24