Re: Networking Puzzle

On Sat, 18 Feb 2006 22:42:10 +0000
Cian Hughes <cianlists_at_cian.ws> wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Here is one for those of you that like a challenge:
> I have a freebsd 7-current box, it has two interfaces rl0 (connected  
> to wireless link) and rl1 (LAN)
> rl0 has no addresses
> I run PPPoE on rl0 which gives me an static IP address (lets call  
> this 1.2.3.4) and Default Gateway.
> I also have a /29 of public IP's which are routed through this address
> the first address x.x.x.1 is assigned to rl1
> 
> The normal setup is a cisco router on the wireless link, and all  
> computers route through it (but my cisco router is broken).
> 
> Any traffic originating from 1.2.3.4 and going to the outside world  
> is blocked by an upstream firewall that I have no control over,  
> anything in my public range has no upstream firewalling.
> 
> Sysctl is set to forward packets, and machines on the LAN with
> public ips in my range work as expected.
> 
> however if i do something like this:
> ping freebsd.org
> it fails because the packets automatically originate from 1.2.3.4
> 
> if I do this:
> ping -S x.x.x.1 freebsd.org (thus setting the src address to a non- 
> firewalled IP)
> it all goes fine and the packets return.
> 
> Inbound connections (eg ssh) from the internet to x.x.x.1 work, but  
> obviously any web access from my freebsd box fails.
> 
> My Question: How do i set the src address for all outbound packets  
> originating on my machine to x.x.x.1 instead of 1.2.3.4 when they
> are passing through my pppoe tunnel?
> 
> BTW this is not a show stopper for me, I have placed an old PII  
> machine between my server and the pppoe tunnel, which solves it. I'm  
> just curious as to whether or not there is a solution.
> 

I've done something like that before (as ISP).
The tunnel end of the PPPoE link had IP from unofficial range and the
static net with official IPs was routed to this unofficial IP.
This works fine. Can you show me your routing table ?

Marcin