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 From:  "Chris Bagnall" <m0n0wall at minotaur dot cc>
 To:  <Peter Curran>, <m0n0wall at lists dot m0n0 dot ch>
 Subject:  RE: [m0n0wall] Half-bridge modem routing fix
 Date:  Tue, 16 Nov 2004 13:06:50 -0000

> Setup the DSL300T using PPPoA.
> Enable DHCP (set the range etc as you like and set the 
> default gateway as nothing).
> Set the m0n0 to use DHCP on the WAN interface.

Did you have to change the firmware in the end, or did the default config
work fine? I'm deploying one of these combos for a client on Thursday, so
it'd be good to know if I need to flash the modem in advance (and save a
fair amount of time on the day).

> The config will not work on the m0n0 unless you have Adam's 
> patch to dhclient.conf because it is not legal to route 
> packets to yourself (the default route is the WAN IP 
> address).  Adam's patch simply changes the route instruction 
> to send the packets out the WAN interface, bypassing the need 
> for a default route IP.

Yep, Adam's patch automates and does much tidier a similar procedure I found
on a FreeBSD list a few months ago. I had been just applying the route
modification commands via exec.php since my m0n0 box and ADSL modem are
connected to a UPS and hardly ever change IP.

> I have a modified version of Adam's patch that I will send to 
> Manuel for inclusion in later betas.  This is generic and 
> detects the condition (int_IP == def_route_IP) && 
> (netmask==  This is unique to this situation 
> and the correct action is to route via interface rather than address.

It'd be very useful if Manuel did include it in future betas. Whilst I'm
quite happy to execute shell commands on my m0n0 box, I'm not sure clients
would be happy about doing so. It'd mean I could finally deploy m0n0 boxes
to clients with ADSL, rather than IPCop.

Since you seem to know far more about the scenario than I do, any idea why
the modems would be designed to work in this way? I get the impression that
these ADSL modems are relying on a bug in most OSes (in that they'll allow
routing to own IP address). Of course the plan falls apart when these modems
encounter the BSD stack that prevents them from doing this (correctly, from
what I gather).

Have I completely misunderstood? Or does it seem like these modems are
relying on a bug to work properly and we're having to work around the
work-around, as it were?


C.M. Bagnall, Partner, Minotaur
Tel: (07010) 710715   Mobile: (07811) 332969   ICQ: 13350579
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