[wplug] Router issue

James O'Kane jo2y at midnightlinux.com
Fri Jan 10 16:03:48 EST 2003


In addition to what some other people have said, I can give a bit of 
insight why what you're hoping to do might not work. I'm going to call the 
WAN side of the linksys 5 and the IP you want for your server 8. 
In the normal case, the firewall responds when people on the WAN side ask 
'Who has IP 5?' and your firewall reponds, "I do, here is my mac address" 
This is Address Resolution Protocol (ARP). When someone asks "Who has IP 
8?" Your firewall needs to respond with its mac address so the sender 
knows where the packet should go. 
In a bigger world/network, you would have a range of IP addresses, and the 
sender (normally another router) would have a static route on their end 
saying that anything for the 1.2.3.0/24 network should be sent to your 
firewall. In that case, your firewall need not respond to ARP for all of 
the addresses. 

As someone else mentioned, you can either put a hub between the DSL modem, 
and you're two computers, or take a linux machine and put it where your 
firewall is and have it respond to both addresses with ethernet interface 
aliasing. For example:
/sbin/ifconfig eth0 192.168.1.1 
/sbin/ifconfig eth0:1 192.168.1.2

That would make eth0 respond to arp requests for both addresses.


Hope that was helpful to someone.

-james



On Tue, 7 Jan 2003, Henry Umansky wrote:

> OK, I have another issue. Telerama gave me two different static IP 
> addresses, but they are both on two different subnets.  I have a Linksys 
> router connected directly to the DSL modem with the WAN IP (let's say 
> xx.xx.5.xx) and a LAN IP of 192.168.1.1.  Now lets say that Telerama gave 
> me another IP xx.xx.8.xx, is there anyway that I can make my Linux machine 
> the 2nd IP and my router the 1st IP.  My router can let me configure a 
> static routing table and is pretty configurable in terms cheap 4-port 
> routers, but I'm just not sure what to do.  Here's what I thought I needed 
> to do:
> 
> -Set the IP address of the Linux machine to the 2nd static IP
> -set the gateway to my routers IP (192.168.1.1) and set up the DNS
> -and update my routing table on the router
> 
> Can anyone help me with what to do, and if it is just update the routing 
> table, what entry would I need?  I have a feeling I would need to purchase 
> a hub or a switch and connect the router and the Linux box to the hub or 
> switch.
> 
> -Henry
> 
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