[lwip-devel] [bug #31367] Cannot send a UDP datagram to a different valid subnet

[Simon Goldschmidt]

Follow-up Comment #4, bug #31367 (project lwip):

> The simple solution is for the udp receive callback to be passed 
> the netif of the incoming packet

We already have that information: ip_current_netif() returns the netif the
currently processed IP packet was received on - this works for UDP, TCP and
RAW pcbs.

Replying to UDP packets would be nice, but not at the risk of flooding our
ARP cache. From testing, I see that windows seems to record the ARP entry on
reception: when pinging A -> B, I see an ARP request from A asking for B, but
not B asking for A (both hosts did not know each other before).

Even if we did solve this by always keeping the last broadcast ARP in an
extra cache, it would stop to work if your application program would respond
with a short delay (in which another broadcast could be received).

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