[wplug] Router issue

Dave Neuer mr_fred_smoothie at yahoo.com
Fri Jan 10 14:07:37 EST 2003


I am a little confused about what you are trying to
do:

You want the Linux box to have the 2nd static IP (so
it can, for instance, be a server w/ an unchanging and
published IP address), but actually sit behind the
Linksys router so it can share your sole physical
line?

My guess is that the Linksys won't do what you'll need
it to do: but I really don't know that much about
them, I'd just be a little surprised.

If the Linksys is capable of IP aliasing (assigning 2
IPs to one interface) and doing somewhat complex NAT
(destination and source NAT, as opposed to just
masquerading) then it's possible you can tell the
Linksys that it's both IP addresses, and give your
Linux box an unpublished IP address and have the
Linksys do the translation. I.e., the Linksys would
have NAT rules which say, static IP 1 is going to this
LAN, static IP 2 is going to this machine; internal
machines 1 through N get their packets' source address
changed to static IP 1, machine N + 1 gets its
packets' address changed to static IP 2.

See what I mean? It's not a question of routing
tables, the Linksys (or whatever sits at the end of
your WAN line) needs to advertise both static IPs --
which MUST be the ones Telerama assigned you, not
reserved internal IPs which you picked out -- for the
packets to go through it. The machines on the other
side cannot then also have that address -- unless you
have a bridge, which is something different.

My suggestion would be to ditch the Linksys and set up
a Linux box w/ 3 NICs and set up iptables rules to do
what I've described above, along w/ whatever firewall
behavior you need.

If you don't think you can figure out how to do it,
I'm unemployed, so you could hire me (cheap!) to do it
for you.

Dave

PS -- as a side note, if what I've described above is
really your intention and you don't want the other
machines on your LAN to be addressable from the
outside, you don't even need 2 static IPs, just the
rules which deal w/ incoming packets, so you could get
away with only paying Telerama for one IP. I still
think you'd need to ditch the Linksys, but you'll want
to consult the Linksys manual to see if it can do the
fairly complex NAT/Masquerading involved.

If there's someone on this list who knows more about
the functionality of Linksys home routers and I'm
wrong, please chime in.

--- Henry Umansky <hmust2+ at pitt.edu> 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
> 
> _______________________________________________
> wplug mailing list
> wplug at wplug.org
> http://www.wplug.org/mailman/listinfo/wplug


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