Re: [lwip-users] 1.2.0 etharp_ip_input change

[Jonathan Larmour]

Kieran Mansley wrote:
> On Tue, 2007-01-02 at 17:50 +0000, Jonathan Larmour wrote:
> > I was wondering about the following change in 1.2.0. Isn't updating the ARP 
> > table from incoming IP packets a good thing and normal practice? Otherwise 
> > for something which isn't already in the ARP cache (especially a new TCP 
> > connection, or UDP from a novel host) won't the lwip stack need to send an 
> > ARP request for any response?
>
> There is a moderate spoofing problem with that approach, as you
> essentially take it as given that the person who sent you the packet
> isn't lying about their MAC address.  By always checking it (by sending
> a broadcast ARP request) you give yourself at least a little protection
> from such things.

Very little indeed, unfortunately, unless it was by accident, not 
intentionally.

> Whether the efficiency of avoiding the ARP outweighs
> the paranoia of always checking is perhaps up to the local network
> manager, and we should perhaps consider it as a compile time option.

I'll submit a patch for this then.

Jifl
--
--["No sense being pessimistic, it wouldn't work anyway"]-- Opinions==mine