Re: [lwip-devel] Suggestion re ARP

[Leon Woestenberg]

Hello Florian,

Zschocke, Florian wrote:

> Leon Woestenberg wrote on Thursday, April 29, 2004 10:52 AM:
>
>
> > That´s true. But I am talking about inbound *IP* traffic
> > accepted by the local host (running lwIP). In this case, should
> > inbound packets result in their source address being add to the
> > ARP cache? 
>
>
> Maybe I misinterpreted you saying that the algorithm is "protocol agnostic".
>
My fault. It is not, as you quoted below. Sorry for the confusion.

> The algorithm described in RFC 826 does only act on ARP packets. Quote:
> "When an address resolution packet is received, the receiving Ethernet
> module gives the packet to the Address Resolution module which goes through
> an algorithm similar to the following."
>
> So any ARP cache updates are done only when an ARP packet was received.
> Normal IP traffic does not affect the ARP cache.

I remember I have added this to lwIP because lwIP would always lose at
least one packet when replying to a new host, because there was no
packet queueing on unresolved ARP entries.

As currently, the outgoing packet queue is still under development
(stable, but lacking support for >1 packet) I will leave it this way.

After it is finished, I can remove etharp_ip_input() AND always enable
packet queueing. I am not sure if this is what all users want though?

BTW, I have to decide on a way to balance the amount of packets on
queue, and a heuristic to throw them away after ARP timer ticks.
RFC on that one...

Regards,

Leon.


/**
 * Updates the ARP table using the given IP packet.
 *
 * Uses the incoming IP packet's source address to update the
 * ARP cache for the local network. The function does not alter
 * or free the packet. This function must be called before the
 * packet p is passed to the IP layer.
 *
 * @param netif The lwIP network interface on which the IP packet pbuf 
arrived.
 * @param pbuf The IP packet that arrived on netif.
 *
 * @return NULL
 *
 * @see pbuf_free()
 */
struct pbuf *
etharp_ip_input(struct netif *netif, struct pbuf *p)