multihome network

alexus alexus at
Fri Nov 16 08:50:48 PST 2007

my private IP that eventually resolves to public IP through PIX is
different then coming from my other public IP that assigned on my fxp1
that comes from another ISP, the fxp1 IP already configured this way
so it pass everything to my box

what i've tried is adding route on my box

route add

still not go:(

On Nov 16, 2007 8:54 AM, Steve Bertrand <iaccounts at> wrote:
> Girish Venkatachalam wrote:
> > On 00:18:42 Nov 16, alexus wrote:
> >> Hello,
> >>
> >> I have two NICs on my box, one (primary) connected to switch and have
> >> private IP. that IP also have a static route on Cisco PIX for
> >> accessing this box from outside. the other interface has public IP
> >> that is connected to another switch, i configure both IPs through
> >> /etc/rc.conf, but I can not for some reason access my box through that
> >> public IP, no firewall rules would prevent me from doing so. here is
> >> my output for netstat -rn
> >>
> -- snip
> > Your default route is and not
> Yes, but if he changes that, then he won't be able to access the box via
> the PIX (private) connection.
> I will make these assumptions, then elaborate:
> The box in question is at your office. You are at home trying to access
> it. The connection works by connecting to the public IP of the PIX (that
> gets port-forwarded back), but does not work when accessing the direct
> Internet facing port.
> I'm willing to bet that if you run a tcpdump on your machine at home you
> are attempting the connection to the 216.112.241.x IP, you will actually
> find that the machine is getting back to you just fine. However, many
> OS's will drop a 'spoofed' packet. Essentially what is likely happening
> is this:
> - you send from home a packet to 216.112.241.x.
> - the office router/box accepts it
> - the office router looks up in it's routing table a path back to your
> home IP
> - it has no particular route, so it sends it out the default gateway
> (
> - your pc at home notices that the packet was sent to a destination IP,
> but it came back from a different one (the outside IP of the PIX)
> - the packet is dropped as the source address is spoofed
> There are a couple ways to fix this. The first and easiest is if you are
> only trying to connect to this box's public IP from one location, add a
> static route on the office box to that network that routes to it's
> public upstream
> The other way is to utilize policy-based routing. IPFW can do this, and
> (from what I understand) so can PF. (In Cisco-land, you would use a
> route-map).
> Steve
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