how to route

how to route

[Nicolas Patik]

I have 2 linux boxes connected to a switch:

box1: 
eth0 192.168.0.200/255.255.255.0
eth1 public address from ISP dhcp

box2: 
eth0 192.168.0.35/255.255.255.0

box3:
eth0 192.168.1.3/255.255.255.0

I want box1 to act as a gateway to the internet 
(it is doing this now for box2), 
but also want to communicate from box2 to box3 through box1, 
and that box3 can use the internet through box1.

how can I do this?


TIA,

--Nicolas
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RE: how to route

[Rajat Jain, Noida]

Hi,

I don't think box3 would be able to box1 or box2 currently. This is because
the IP address you've assigned to box3 is not on the same subnet as that of
box1 & box2. Box1 and box2 are right now on subnet 192.168.0.0. Where as
box3 is is not subnet 192.168.1.0. To connect PCs on different subnets you
need to have a router in between. 

The options you have:

1) Make the IP addresses of all three boxes on the same subnet by changing
box3's IP to 192.168.0.*, OR box1 & box2's IP to 192.168.1.*

2) Make subnet larget by making subnet mask = 255.255.0.0 or some thing.

-Rajat

-----Original Message-----
From: linux-newbie-owner@vger.kernel.org
[mailto:linux-newbie-owner@vger.kernel.org] On Behalf Of Nicolas Patik
Sent: Friday, December 24, 2004 9:30 AM
To: linux-newbie@vger.kernel.org
Subject: how to route

I have 2 linux boxes connected to a switch:

box1: 
eth0 192.168.0.200/255.255.255.0
eth1 public address from ISP dhcp

box2: 
eth0 192.168.0.35/255.255.255.0

box3:
eth0 192.168.1.3/255.255.255.0

I want box1 to act as a gateway to the internet (it is doing this now for
box2), but also want to communicate from box2 to box3 through box1, and that
box3 can use the internet through box1.

how can I do this?


TIA,

--Nicolas
-
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Re: how to route

[Greg Olszewski]

Nicolas Patik wrote:
> I have 2 linux boxes connected to a switch:
3, no?

> 
> box1: 
> eth0 192.168.0.200/255.255.255.0
> eth1 public address from ISP dhcp
> 
> box2: 
> eth0 192.168.0.35/255.255.255.0
> 
> box3:
> eth0 192.168.1.3/255.255.255.0
> 
> I want box1 to act as a gateway to the internet 
> (it is doing this now for box2), 
> but also want to communicate from box2 to box3 through box1, 
> and that box3 can use the internet through box1.
> 
> how can I do this?
>

You could create an alias for eth0 on box1 which is on the same subnet 
as box 3, like so:

box1# ifconfig eth0:0 192.168.1.200 netmask 255.255.255.0

now, from box1 you should be able to ping box3 and vice-versa:

box1# ping 192.168.1.3 -c 1
PING 192.168.1.3 (192.168.1.3): 56 data bytes
64 bytes from 192.168.1.3: icmp_seq=0 ttl=127 time=3.0 ms

--- 192.168.1.3 ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 3.0/3.0/3.0 ms

and

box3$ ping 192.168.1.200 -c 1
...


now you'll need to make sure box3 is using box1 as it's gateway

box3# route del default
box3# route add default gw 192.168.1.200

provided that this works, you ought to be able to ping box2 from box3
and vice versa, although this depends on box1's ipchains/iptables rules 
(some must be set up if box1 is acting as a gateway). If you posted the
output of 'iptables -L -n' and 'iptables -t nat -L -n', I could be sure, 
but the iptables rules you'll want are something like so:

#first flush the tables
iptables -t nat -F
iptables -F
#drop FORWARD packets by default
iptables -P FORWARD DROP
# unless there is a connection established
iptables -A FORWARD -m state --state ESTABLISHED -j ACCEPT

# or it came in on eth0(or :0), and is leaving the same way,
# and is addressed to a local address
iptables -A FORWARD -i eth0+ -o eth0+ -d 192.168.0.0/23 -s 
192.168.0.0/23 -j ACCEPT

# Or it is an internal packet heading for the world
iptables -A FORWARD -i eth0+ -o eth1 -s 192.168.0.0/23 -d \! 192.168.0.0/23

# now masquerade all outgoing packets
iptables -t nat -A POSTROUTING -s 192.168.0.0/23 -d \! 192.168.0.0/23 -j 
MASQUERADE

have fun,

greg

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