Promiscuous Mode

[deckhard]

Hi

I want to use Promiscuous Mode with LWIP+STM32H743.

I want to be able to capture frames not sent over to my IP address.

Is it possible?

Thanks

[waclawek.jan]

JW

[deckhard]

Once that bit is set how do I capture the packets via LWIP?

[waclawek.jan]

I'm not interested in this particular problem; lwip is open source and has its own suport mail forum.

A quick look at the sources (lwip 1.4) shows that in ip.c:in_input(), addressed packets which are not addressed to us are considered for forwarding, if IP_FORWARD is defined. In lwip 2, things get muddier thanks to extensive ipv6 support, in ip4.c:ip4_input() I see the same pattern though. So, you may want to hook up your code somewhere there; or maybe even one level lower, at the packet driver level, just after reception.

JW

[deckhard]

To my understanding LWIP IP_FORWARD definition is for two NICs on the same board.

[waclawek.jan]

Yes. The intention of that code is, "if it's not for IP bound to this interface, it may be the other interface(s)".

What I said is, that that might be the place to splice in your code handling the unicast packets with not-own-IP.

JW

[deckhard]

While that might be a good idea, what about ARP reply? would the packets even get there if someone else's answered the ARP request?

[waclawek.jan · Accepted solution]

Yes, you have to use a hub, or a managed switch with properly configured port forwarding.

But this is entirely unrelated to STM32 or lwip.

JW

[deckhard]

Yes exactly