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 From:  "Chris Bagnall" <m0n0wall at minotaur dot cc>
 To:  <m0n0wall at lists dot m0n0 dot ch>
 Subject:  RE: [m0n0wall] For anyone using a Dlink 300T or X-modem
 Date:  Mon, 21 Nov 2005 19:58:21 -0000
> yeah, the only time this is required, if I'm thinking of the 
> right issue, is in situations like where your ISP gives you a 
> default gateway IP that isn't on your WAN subnet, or 
> something equally ridiculous, poorly designed, and ignoring 
> network best practices (and RFC's for that matter).

It's not necessarily the ISP's fault - it's the way PPPoA half-bridge ADSL
modems work. The default gateway is in fact the same as the WAN IP, which
confuses the BSD network stack into sending traffic out over loopback rather
than onto the interface itself.

Yes, it's a messy hack, but it's less messy in my view than double-natting,
which is the only other option if you've got a dynamic IP from the ISP
(rather than a routed subnet).

Since nearly all ADSL here in the UK is PPPoA (yes, I know some exchanges
support PPPoE unofficially, but it's very hit-and-miss), it's a pretty
common issue for folks this side of the pond.


C.M. Bagnall, Director, Minotaur I.T. Limited
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