[CentOS] Routing issue between 2 LANs

Sun Dec 19 20:17:01 UTC 2010
Michel van Deventer <michel at van.deventer.cx>

Hi,

> >>> The Fedora box (1. network):
> >>> [jose at IDi ~]$ ping 192.168.236.80
> >>> PING 192.168.236.80 (192.168.236.80) 56(84) bytes of data.
> >>> 64 bytes from 192.168.236.80: icmp_req=1 ttl=64 time=1.61 ms
> >>> 64 bytes from 192.168.236.80: icmp_req=2 ttl=64 time=0.684 ms
> >>> [jose at IDi ~]$ ifconfig eth0 | grep -i 'inet addr'
> >>>            inet addr:192.168.1.3  Bcast:192.168.1.255  Mask:255.255.255.0
> >>
> >> This doesn't make much sense without a route.  Can you try a traceroute to the
> >> fedora box address from the 192.168.236.80 box to see how/why it gets there?
> >
> > Sure, here it is:
> >
> >> From fresh reboot of the Fedora14 box:
> >
> > [jose at IDi ~]$ su -
> > Contraseña:
> > [root at IDi ~]# route add -net 192.168.236.0 netmask 255.255.255.0 gw 192.168.1.100 dev eth0
> > [root at IDi ~]# logout
> >
> > [jose at IDi ~]$ traceroute 192.168.236.80
> > traceroute to 192.168.236.80 (192.168.236.80), 30 hops max, 60 byte packets
> >   1  puente (192.168.1.100)  0.286 ms  0.260 ms  0.239 ms
> >   2  192.168.236.80 (192.168.236.80)  0.963 ms !X  0.949 ms !X  0.930 ms !X
> 
> We know why it works this direction.
> 
> > [jose at IDi ~]$ ping 192.168.236.80
> > PING 192.168.236.80 (192.168.236.80) 56(84) bytes of data.
> > 64 bytes from 192.168.236.80: icmp_req=1 ttl=64 time=0.668 ms
> > 64 bytes from 192.168.236.80: icmp_req=2 ttl=64 time=0.599 ms
> > 64 bytes from 192.168.236.80: icmp_req=3 ttl=64 time=0.566 ms
> > ^C
> > --- 192.168.236.80 ping statistics ---
> > 3 packets transmitted, 3 received, 0% packet loss, time 2000ms
> > rtt min/avg/max/mdev = 0.566/0.611/0.668/0.042 ms
> >
> > [jose at IDi ~]$ ssh 192.168.236.80
> > jose at 192.168.236.80's password:
> > Last login: Sun Dec 19 20:44:44 2010 from 192.168.1.3
> > [jose at control ~]$
> 
> I wanted the reverse path.  Traceroute from the 192.168.236.80 box back to the 
> fedora address.  It doesn't make sense that it can return packets without a 
> route going through the Centos box.
Yes it does make sense, if the machine in the 192.168.236.0/24 has the
centos box in the middle (the one with two LAN cards) as a default
route, then you wouldn't need a seperate route. Packets would come back.
Can you give the network settings for 192.168.236.80 ?

Can you tell us more about the network setup ? routers in both
networks ? Maybe a quick drawing should make things more clear.

If you cannot set a route on the various devices it might help to use
proxy-arp.

	regards,

	Michel