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Re: [lwip-users] IP forwarding to/from PPP working for one netif, but no

From: address@hidden
Subject: Re: [lwip-users] IP forwarding to/from PPP working for one netif, but not another
Date: Tue, 11 Feb 2020 11:47:04 +0100
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2

Am 11.02.2020 um 10:20 schrieb Andrew Pullin:
> [..]
> The part that I am stuck on presently is that Host2 has no knowledge of 
> how to route packets from PPP out to the WAN, say,
> Between ip4_forward, IP_FORWARD, ip4_route_src, LWIP_HOOK_IP4_ROUTE, 
> LWIP_HOOK_IP4_ROUTE_SRC, and the ESP32 port modifications, I am not 
> quite sure where to make the right intervention. It is ... a lot to take in.
> As far as I understand the standard usage of the stack for a single 
> netif, outgoing packets elide the entire forwarding/routing system 
> because they are specified to be transmitted on a particular netif? Is 
> that right?
> Fundamentally, I only have eth0 and pp1  (to use the lwip netif naming 
> system) and anything not specifically with IP dest = eth0 or pp1 should 
> be sent on towards Host2's gateway (after NAT source address IP rewriting).
> Is that logically complete, and if so, where should it be implemented?

I would think you'd just set the ppp netif as default netif (so it is
just used for all outgoing trafic where no better route is found) and
keep eth0 without a gateway (which should ensure only matching subnet
packets are transmitted on this netif).


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