Subject: Re: NAT (was Re: IPv6 Comment)
To: Andrew Gillham <>
From: Andrew Brown <>
List: current-users
Date: 09/07/2000 13:45:40
>> his cable modem uses regular old 33.6 dialup to send outbound traffic.
>> as a result, he gets nice input, but almost no output.  what i did for
>> him was set up a nat gateway on one of his machines (the one to which
>> the cable modem delivers inbound traffic --- he has only one address)
>> and set up *that* machine with a default route to his isdn provider.
>> the result is he gets 112k outbound instead of 33.6, and a big fat
>> round routing path.
>Yes, I like this concept, but does it work by setting the source address
>on the ISDN packets to the cable modem address?  If that is the case
>this is broken by anti-spoofing access lists on the ISDN provider's
>end.  As ISPs move (slowly) towards filtering inbound traffic from
>their customers to only allow valid source addresses this type of thing
>just flat doesn't work.

yep, that's exactly how it works.  the only trick was "borrowing"
another ip address from the cable modem provider (for the local isdn
endpoint) so that the outbound traffic would get properly nat'ed.

his isdn provider doesn't do source filtering, but then again...he's
on retainer there to help with stuff like that, so he's pretty much

|-----< "CODE WARRIOR" >-----|             * "ah!  i see you have the internet (Andrew Brown)                that goes *ping*!"       * "information is power -- share the wealth."