[GitHub] [incubator-nuttx] anchao commented on pull request #3586: Revert a change that accepted UDP packets not destined for us.

[GitBox <gi...@apache.org>]

anchao commented on pull request #3586:
URL: https://github.com/apache/incubator-nuttx/pull/3586#issuecomment-824572981


   The purpose of make changing here is that the nuttx device can't get the address through dhcpc in unicast mode. In further investigation, I found that the dhcpc OFFER message has been discarded by IP layer:
   
   https://github.com/apache/incubator-nuttx/blob/ae420057120a8dcc59eb6104b36278ba09cfce17/net/devif/ipv4_input.c#L262
   
   dev->d_ipaddr address is INADDR_ANY by default, which will causes the unicast directional message to be discarded by mistake, referring to other protocol stacks, this is incorrect. if the network card address is INADDR_ANY, UDP packets need to be discarded by the UDP stack:
   
   1. IP drop
   
   ```
   NUTTX(DHCPC)              ->  HOSTAP(DHCPD)
   0.0.0.0                   ->  255.255.255.255   DISCOVER
   100.1.1.1 (unicast)       ->  100.1.1.4         OFFER       <-- IP drop
   ```
   
   https://github.com/apache/incubator-nuttx/blob/ae420057120a8dcc59eb6104b36278ba09cfce17/net/devif/ipv4_input.c#L312
   
   2. After patch:
   ```
   NUTTX(DHCPC)              ->  HOSTAP(DHCPD)
   0.0.0.0                   ->  255.255.255.255   DISCOVER
   100.1.1.1 (unicast)       ->  100.1.1.4         OFFER       <-- IP bypass the udp packet
   0.0.0.0                   ->  255.255.255.255   REQUEST
   100.1.1.1 (unicast)       ->  100.1.1.4         ACK
   ```


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