[Ilugc] NAT/Port forwarding on a DAX Router
- From: siva@xxxxxxxxxxx (Sivasankar Chander)
- Date: Mon Dec 13 16:24:25 2004
How do I check for DNAT support in my router?
If it's not in the manual or the configuration page,
then it's probably not enabled. You can try poking
around using ssh (into the LAN-side interface of the
router), but there will most probably be a root
password set, and sshd may not be running on the
router. Try telnet as well.
My router uses PPPoA and its not a USB DSL Modem.
It's an ethernet based router.
There's nothing further that you can do with the
ISP-provided router, since it's mostly a black box.
Internally, on the WAN side, it obviously interfaces to
the cable provided by the ISP. This is probably just
a stock DSL DMT or G.lite chipset that appears internal
to the router as a PPPoA interface (assuming it's
a Linux router). It then routes and NATs from that
interface to its LAN-facing Ethernet interface.
With a routerlinux setup, it does exactly the same
thing, except that the routerlinux box is a 'white box'
or even a 'glass box', that replaces the 'black box'
provided by the ISP. With routerlinux, you would need
to use the ISP-provided USB DSL modem instead of their
broadband router. The USB DSL modem would connect to
the routerlinux box (with the right driver stack, this
would then appear inside the routerlinux system as a
PPPoA interface). You can then do anything with the
PPPoA interface - at least anything that netfilter/iptables
supports, including DNAT.
What's the advantage of this setup? The USB DSL modem
option is usually less expensive, and you have full
control over netfilter/iptables, so you have a fully
configurable firewall - with the right utilities,
you can do lots of useful things, including support
for multiple ISPs, bonding, fallback routing, load
balancing, multiple zoning (DMZs), etc.
The downside is that
you need a minimal PC to run routerlinux - any old 486/
Pentium with 16 MB of RAM, a small hard disk and a
couple of ethernet NICs should be fine. For a more
robust embedded platform, look for a Soekris Engineering
Elan platform or a GCT/Allwell Eden platform - both
these are expensive (~$200-$300) alternatives.
-Siva
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