Routing using Linux with 2 NIC cards

Question

Configured Clear OS to be in Gateway mode on a machine with two NIC cards.

eth0:192.168.2.0/24 with ip 192.168.2.27 which is connected to a modem and thus have internet connectivity.

eth1:192.168.122.0/24 with ip 192.168.122.10 which is connected to other machines in LAN through switch.

LAN machines with network 192.168.122.0 is not getting internet.How can they get internet Through Clear OS gateway.I have enabled packet forwarding in clear os using "ip_forward=1" What am i missing?.Can you please help me in this.

Following are the static routing i have added: on LAN machine1 with ip address 192.168.122.11

ip route add 192.168.2.0/24 via 192.168.122.10 dev eth0

ip route show

192.168.2.0/24 via 192.168.122.10 dev eth0 
192.168.122.0/24 dev eth0  proto kernel  scope link  src 192.168.122.11

But still 192.168.2.0/24 network is not reachable.Where can be the problem??

EDIT: All the machines are Virtual Machines running on xen.

Network 192.168.2.0/24 is through Bridge network with host Ethernet card and network 192.168.122.0/24 is through virtual bridge network with in VMs.

You forgot to setup nat http://www.revsys.com/writings/quicktips/nat.html — , Oct 11 '12 at 08:13
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE iptables -A FORWARD -i eth0 -o eth1 -m state --state RELATED,ESTABLISHED -j ACCEPT. iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT. But still Its not reachable. :( — Kevin Parker, Oct 11 '12 at 08:34
Did you echo `echo 1 > /proc/sys/net/ipv4/ip_forward` *and* put `net.ipv4.ip_forward = 1` into `/etc/sysctl.conf`? — Tom O'Connor, Oct 11 '12 at 09:20

score 1 · Answer 1 · answered Oct 11 '12 at 13:07

If Xen has configured a bridge network to connect the VM guests to the hosts LAN interface, then the guests should not be in a separate IP subnet. A "bridge" connects two networks which are disjoint at the 'hardware' (i.e. Ethernet) level. In that case, all machines, virtual and physical, should have addresses in 192.168.2.0/24 .

If, on the other hand, the physical LAN and virtual LAN are not bridged, then you will want separate IP subnets, with routing between them. NAT (on the Linux host) is optional, though it might be necessary if your Internet "modem" device is only expecting to provide access to one IP subnet. If you do things this way, then you will need to configure the guests to use 192.168.122.10 as their default gateway.

score -1 · Answer 2 · answered Oct 12 '12 at 04:25

-1

It worked on a real machine.i dont know why it didnt work on VM.But when i tried the same set up on real hardware it worked.Can some one please give me an explanation to this.?

answered Oct 12 '12 at 04:25

Kevin Parker

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Routing using Linux with 2 NIC cards

2 Answers2