etharp.c File Reference

#include "lwip/opt.h"
#include "lwip/etharp.h"
#include "lwip/stats.h"
#include "lwip/snmp.h"
#include "lwip/dhcp.h"
#include "lwip/autoip.h"
#include "lwip/prot/iana.h"
#include "netif/ethernet.h"
#include <string.h>
#include "path/to/my/lwip_hooks.h"

Macros
#define	ARP_AGE_REREQUEST_USED_UNICAST   (ARP_MAXAGE - 30)
#define	ARP_MAXPENDING   5
#define	ETHARP_FLAG_TRY_HARD   1

Enumerations
enum	etharp_state

Functions
void	etharp_tmr (void)
void	etharp_cleanup_netif (struct netif *netif)
ssize_t	etharp_find_addr (struct netif *netif, const ip4_addr_t *ipaddr, struct eth_addr **eth_ret, const ip4_addr_t **ip_ret)
int	etharp_get_entry (size_t i, ip4_addr_t **ipaddr, struct netif **netif, struct eth_addr **eth_ret)
void	etharp_input (struct pbuf *p, struct netif *netif)
err_t	etharp_output (struct netif *netif, struct pbuf *q, const ip4_addr_t *ipaddr)
err_t	etharp_query (struct netif *netif, const ip4_addr_t *ipaddr, struct pbuf *q)
err_t	etharp_request (struct netif *netif, const ip4_addr_t *ipaddr)

Detailed Description

Address Resolution Protocol module for IP over Ethernet

Functionally, ARP is divided into two parts. The first maps an IP address to a physical address when sending a packet, and the second part answers requests from other machines for our physical address.

This implementation complies with RFC 826 (Ethernet ARP). It supports Gratuitious ARP from RFC3220 (IP Mobility Support for IPv4) section 4.6 if an interface calls etharp_gratuitous(our_netif) upon address change.

Macro Definition Documentation

ARP_AGE_REREQUEST_USED_UNICAST

#define ARP_AGE_REREQUEST_USED_UNICAST   (ARP_MAXAGE - 30)

Re-request a used ARP entry 1 minute before it would expire to prevent breaking a steadily used connection because the ARP entry timed out.

ARP_MAXPENDING

#define ARP_MAXPENDING   5

the time an ARP entry stays pending after first request, for ARP_TMR_INTERVAL = 1000, this is 10 seconds.

ETHARP_FLAG_TRY_HARD

#define ETHARP_FLAG_TRY_HARD   1

Try hard to create a new entry - we want the IP address to appear in the cache (even if this means removing an active entry or so).

Enumeration Type Documentation

etharp_state

enum etharp_state

ARP states

Function Documentation

etharp_cleanup_netif()

void etharp_cleanup_netif

(

struct netif *

netif

)

Remove all ARP table entries of the specified netif.

Parameters

netif

points to a network interface

etharp_find_addr()

ssize_t etharp_find_addr	(	struct netif *	netif,
		const ip4_addr_t *	ipaddr,
		struct eth_addr **	eth_ret,
		const ip4_addr_t **	ip_ret
	)

Finds (stable) ethernet/IP address pair from ARP table using interface and IP address index.

Note

the addresses in the ARP table are in network order!

Parameters

netif	points to interface index
ipaddr	points to the (network order) IP address index
eth_ret	points to return pointer
ip_ret	points to return pointer

Returns

table index if found, -1 otherwise

etharp_get_entry()

int etharp_get_entry	(	size_t	i,
		ip4_addr_t **	ipaddr,
		struct netif **	netif,
		struct eth_addr **	eth_ret
	)

Possibility to iterate over stable ARP table entries

Parameters

i	entry number, 0 to ARP_TABLE_SIZE
ipaddr	return value: IP address
netif	return value: points to interface
eth_ret	return value: ETH address

Returns

1 on valid index, 0 otherwise

etharp_input()

void etharp_input	(	struct pbuf *	p,
		struct netif *	netif
	)

Responds to ARP requests to us. Upon ARP replies to us, add entry to cache send out queued IP packets. Updates cache with snooped address pairs.

Should be called for incoming ARP packets. The pbuf in the argument is freed by this function.

Parameters

p	The ARP packet that arrived on netif. Is freed by this function.
netif	The lwIP network interface on which the ARP packet pbuf arrived.

See also

pbuf_free()

etharp_output()

err_t etharp_output	(	struct netif *	netif,
		struct pbuf *	q,
		const ip4_addr_t *	ipaddr
	)

Resolve and fill-in Ethernet address header for outgoing IP packet.

For IP multicast and broadcast, corresponding Ethernet addresses are selected and the packet is transmitted on the link.

For unicast addresses, the packet is submitted to etharp_query(). In case the IP address is outside the local network, the IP address of the gateway is used.

Parameters

netif	The lwIP network interface which the IP packet will be sent on.
q	The pbuf(s) containing the IP packet to be sent.
ipaddr	The IP address of the packet destination.

Returns

• ERR_RTE No route to destination (no gateway to external networks), or the return type of either etharp_query() or ethernet_output().

etharp_query()

err_t etharp_query	(	struct netif *	netif,
		const ip4_addr_t *	ipaddr,
		struct pbuf *	q
	)

Send an ARP request for the given IP address and/or queue a packet.

If the IP address was not yet in the cache, a pending ARP cache entry is added and an ARP request is sent for the given address. The packet is queued on this entry.

If the IP address was already pending in the cache, a new ARP request is sent for the given address. The packet is queued on this entry.

If the IP address was already stable in the cache, and a packet is given, it is directly sent and no ARP request is sent out.

If the IP address was already stable in the cache, and no packet is given, an ARP request is sent out.

Parameters

netif	The lwIP network interface on which ipaddr must be queried for.
ipaddr	The IP address to be resolved.
q	If non-NULL, a pbuf that must be delivered to the IP address. q is not freed by this function.

Note

q must only be ONE packet, not a packet queue!

Returns

• ERR_BUF Could not make room for Ethernet header.
• ERR_MEM Hardware address unknown, and no more ARP entries available to query for address or queue the packet.
• ERR_MEM Could not queue packet due to memory shortage.
• ERR_RTE No route to destination (no gateway to external networks).
• ERR_ARG Non-unicast address given, those will not appear in ARP cache.

etharp_request()

err_t etharp_request	(	struct netif *	netif,
		const ip4_addr_t *	ipaddr
	)

Send an ARP request packet asking for ipaddr.

Parameters

netif	the lwip network interface on which to send the request
ipaddr	the IP address for which to ask

Returns

ERR_OK if the request has been sent ERR_MEM if the ARP packet couldn't be allocated any other err_t on failure

etharp_tmr()

void etharp_tmr

(

void

)

Clears expired entries in the ARP table.

This function should be called every ARP_TMR_INTERVAL milliseconds (1 second), in order to expire entries in the ARP table.