Re: [lwip-users] How to limit the UDP Rx packet size to avoid big RAM allocations

[address@hidden]

On 19.06.2018 18:11, Sergio R. Caprile wrote:
> UDP datagrams are carried by Ethernet frames. It is not lwIP but your
> driver who allocates memory to hold those frames before handling them to
> lwIP, which in turn will deliver to your application. The only way to
> stop allocation is there.
> Someone could also send pings of death, repeated SYNs...
> If you need firewall functionality, you need to build a firewall.

Well, the OP was not really asking about a firewall but about DoS 
protection. And he's correct in that to prevent DoS, a device must be 
able to keep up receiving at full wire speed, wether the packets are 
short or long.

But you are right here that throwing packets away in the driver as early 
as possible is the best way to achieve this on a resource constrained 
target. Of course, this makes the driver depend on the application in 
some kind of way, but I wouldn't consider it bad design if it was 
clearly separated from the driver.

You're also right that lwIP can't really help here :-)

Simon