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.

#include "lwip/opt.h"
#include "lwip/ip_addr.h"
#include "lwip/def.h"
#include "lwip/ip.h"
#include "lwip/stats.h"
#include "lwip/snmp.h"
#include "lwip/dhcp.h"
#include "lwip/autoip.h"
#include "netif/etharp.h"
#include <string.h>

Data Structures
struct	etharp_entry

Macros
#define	ARP_AGE_REREQUEST_USED (ARP_MAXAGE - 12)
	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. More...

#define	ARP_MAXAGE 240
	the time an ARP entry stays valid after its last update, for ARP_TMR_INTERVAL = 5000, this is (240 * 5) seconds = 20 minutes. More...

#define	ARP_MAXPENDING 2
	the time an ARP entry stays pending after first request, for ARP_TMR_INTERVAL = 5000, this is (2 * 5) seconds = 10 seconds. More...

#define	ETHARP_FLAG_FIND_ONLY 2

#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). More...

#define	ETHARP_SET_HINT(netif, hint) (etharp_cached_entry = (hint))

#define	free_etharp_q(q) pbuf_free(q)
	Compatibility define: free the queued pbuf. More...

#define	HWTYPE_ETHERNET 1

#define	LL_MULTICAST_ADDR_0 0x01
	The 24-bit IANA multicast OUI is 01-00-5e: More...

#define	LL_MULTICAST_ADDR_1 0x00

#define	LL_MULTICAST_ADDR_2 0x5e

Enumerations
enum	etharp_state { ETHARP_STATE_EMPTY = 0, ETHARP_STATE_PENDING, ETHARP_STATE_STABLE, ETHARP_STATE_STABLE_REREQUESTING }

Functions
static void	etharp_arp_input (struct netif netif, struct eth_addr ethaddr, struct pbuf *p)
	Responds to ARP requests to us. More...

void	etharp_cleanup_netif (struct netif *netif)
	Remove all ARP table entries of the specified netif. More...

s8_t	etharp_find_addr (struct netif netif, ip_addr_t ipaddr, struct eth_addr eth_ret, ip_addr_t ip_ret)
	Finds (stable) ethernet/IP address pair from ARP table using interface and IP address index. More...

static s8_t	etharp_find_entry (ip_addr_t *ipaddr, u8_t flags)
	Search the ARP table for a matching or new entry. More...

static void	etharp_free_entry (int i)
	Clean up ARP table entries. More...

err_t	etharp_output (struct netif netif, struct pbuf q, ip_addr_t *ipaddr)
	Resolve and fill-in Ethernet address header for outgoing IP packet. More...

static err_t	etharp_output_to_arp_index (struct netif netif, struct pbuf q, u8_t arp_idx)
	Just a small helper function that sends a pbuf to an ethernet address in the arp_table specified by the index 'arp_idx'. More...

err_t	etharp_query (struct netif netif, ip_addr_t ipaddr, struct pbuf *q)
	Send an ARP request for the given IP address and/or queue a packet. More...

static err_t	etharp_raw (struct netif netif, const struct eth_addr ethsrc_addr, const struct eth_addr ethdst_addr, const struct eth_addr hwsrc_addr, const ip_addr_t ipsrc_addr, const struct eth_addr hwdst_addr, const ip_addr_t *ipdst_addr, const u16_t opcode)
	Send a raw ARP packet (opcode and all addresses can be modified) More...

err_t	etharp_request (struct netif netif, ip_addr_t ipaddr)
	Send an ARP request packet asking for ipaddr. More...

static err_t	etharp_send_ip (struct netif netif, struct pbuf p, struct eth_addr src, struct eth_addr dst)
	Send an IP packet on the network using netif->linkoutput The ethernet header is filled in before sending. More...

void	etharp_tmr (void)
	Clears expired entries in the ARP table. More...

static err_t	etharp_update_arp_entry (struct netif netif, ip_addr_t ipaddr, struct eth_addr *ethaddr, u8_t flags)
	Update (or insert) a IP/MAC address pair in the ARP cache. More...

err_t	ethernet_input (struct pbuf p, struct netif netif)
	Process received ethernet frames. More...

Variables
static struct etharp_entry	arp_table [ARP_TABLE_SIZE]

static u8_t	etharp_cached_entry

struct eth_addr	ethbroadcast = {{0xff,0xff,0xff,0xff,0xff,0xff}}

struct eth_addr	ethzero = {{0,0,0,0,0,0}}

#define ARP_AGE_REREQUEST_USED (ARP_MAXAGE - 12)

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.

Referenced by etharp_output_to_arp_index().

#define ARP_MAXAGE 240

the time an ARP entry stays valid after its last update, for ARP_TMR_INTERVAL = 5000, this is (240 * 5) seconds = 20 minutes.

Referenced by etharp_tmr().

#define ARP_MAXPENDING 2

the time an ARP entry stays pending after first request, for ARP_TMR_INTERVAL = 5000, this is (2 * 5) seconds = 10 seconds.

Keep this number at least 2, otherwise it might run out instantly if the timeout occurs directly after a request.

Referenced by etharp_tmr().

#define ETHARP_FLAG_FIND_ONLY 2

Referenced by etharp_arp_input(), etharp_find_addr(), etharp_find_entry(), and etharp_update_arp_entry().

#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).

Referenced by etharp_arp_input(), etharp_find_entry(), etharp_query(), and etharp_update_arp_entry().

#define ETHARP_SET_HINT	(	netif,
		hint
	)	(etharp_cached_entry = (hint))

Referenced by etharp_output(), and etharp_query().

#define free_etharp_q ( q ) pbuf_free(q)

Compatibility define: free the queued pbuf.

Referenced by etharp_free_entry().

#define HWTYPE_ETHERNET 1

Referenced by etharp_arp_input(), and etharp_raw().

#define LL_MULTICAST_ADDR_0 0x01

The 24-bit IANA multicast OUI is 01-00-5e:

Referenced by etharp_output(), and ethernet_input().

#define LL_MULTICAST_ADDR_1 0x00

Referenced by etharp_output(), and ethernet_input().

#define LL_MULTICAST_ADDR_2 0x5e

Referenced by etharp_output(), and ethernet_input().

enum etharp_state

Enumerator
ETHARP_STATE_EMPTY
ETHARP_STATE_PENDING
ETHARP_STATE_STABLE
ETHARP_STATE_STABLE_REREQUESTING

static void etharp_arp_input	(	struct netif *	netif,
		struct eth_addr *	ethaddr,
		struct pbuf *	p
	)

static

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

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

Returns: NULL

See Also: pbuf_free()

References ARP_REPLY, ARP_REQUEST, ETHADDR16_COPY, ETHARP_DEBUG, ETHARP_FLAG_FIND_ONLY, ETHARP_FLAG_TRY_HARD, ETHARP_HWADDR_LEN, ETHARP_STATS_INC, etharp_update_arp_entry(), ETHTYPE_IP, ETHTYPE_VLAN, htons, netif::hwaddr_len, HWTYPE_ETHERNET, netif::ip_addr, ip_addr_cmp, ip_addr_isany, ip_addr_islinklocal, IPADDR2_COPY, pbuf::len, netif::linkoutput, LWIP_ASSERT, LWIP_DBG_LEVEL_WARNING, LWIP_DBG_TRACE, LWIP_DEBUGF, LWIP_ERROR(), NULL, pbuf::payload, pbuf_free(), PP_HTONS, S16_F, SIZEOF_ETH_HDR, SIZEOF_ETHARP_PACKET, pbuf::tot_len, and U16_F.

Referenced by ethernet_input().

void etharp_cleanup_netif ( struct netif * netif )

Remove all ARP table entries of the specified netif.

Parameters

netif points to a network interface

References arp_table, etharp_free_entry(), ETHARP_STATE_EMPTY, etharp_entry::state, and netif::state.

Referenced by netif_set_down().

s8_t etharp_find_addr	(	struct netif *	netif,
		ip_addr_t *	ipaddr,
		struct eth_addr **	eth_ret,
		ip_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

References arp_table, etharp_entry::ethaddr, etharp_find_entry(), ETHARP_FLAG_FIND_ONLY, ETHARP_STATE_STABLE, etharp_entry::ipaddr, LWIP_ASSERT, LWIP_UNUSED_ARG, NULL, and netif::state.

static s8_t etharp_find_entry	(	ip_addr_t *	ipaddr,
		u8_t	flags
	)

static

Search the ARP table for a matching or new entry.

If an IP address is given, return a pending or stable ARP entry that matches the address. If no match is found, create a new entry with this address set, but in state ETHARP_EMPTY. The caller must check and possibly change the state of the returned entry.

If ipaddr is NULL, return a initialized new entry in state ETHARP_EMPTY.

In all cases, attempt to create new entries from an empty entry. If no empty entries are available and ETHARP_FLAG_TRY_HARD flag is set, recycle old entries. Heuristic choose the least important entry for recycling.

Parameters

ipaddr	IP address to find in ARP cache, or to add if not found.
flags

See Also: definition of ETHARP_FLAG_*

Parameters

netif netif related to this address (used for NETIF_HWADDRHINT)

Returns: The ARP entry index that matched or is created, ERR_MEM if no entry is found or could be recycled.

a) do a search through the cache, remember candidates b) select candidate entry c) create new entry

References arp_table, etharp_entry::ctime, ERR_MEM, ETHARP_DEBUG, ETHARP_FLAG_FIND_ONLY, ETHARP_FLAG_TRY_HARD, etharp_free_entry(), ETHARP_STATE_EMPTY, ETHARP_STATE_PENDING, ETHARP_STATE_STABLE, ip_addr_cmp, ip_addr_copy, LWIP_ASSERT, LWIP_DBG_TRACE, LWIP_DEBUGF, NULL, etharp_entry::state, and U16_F.

Referenced by etharp_find_addr(), etharp_query(), and etharp_update_arp_entry().

static void etharp_free_entry ( int i )

static

Clean up ARP table entries.

References arp_table, etharp_entry::ctime, etharp_entry::ethaddr, ETHARP_DEBUG, ETHARP_STATE_EMPTY, ethzero, free_etharp_q, ip_addr_set_zero, LWIP_DEBUGF, etharp_entry::netif, NULL, etharp_entry::q, snmp_delete_arpidx_tree, etharp_entry::state, and U16_F.

Referenced by etharp_cleanup_netif(), etharp_find_entry(), etharp_tmr(), and etharp_update_arp_entry().

err_t etharp_output	(	struct netif *	netif,
		struct pbuf *	q,
		ip_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 etharp_send_ip().

References arp_table, ERR_BUF, ERR_RTE, etharp_cached_entry, ETHARP_DEBUG, etharp_output_to_arp_index(), etharp_query(), etharp_send_ip(), ETHARP_SET_HINT, ETHARP_STATE_STABLE, ETHARP_STATS_INC, netif::gw, netif::hwaddr, ip4_addr2, ip4_addr3, ip4_addr4, netif::ip_addr, ip_addr_cmp, ip_addr_isany, ip_addr_isbroadcast, ip_addr_islinklocal, ip_addr_ismulticast, ip_addr_netcmp, LINK_STATS_INC, LL_MULTICAST_ADDR_0, LL_MULTICAST_ADDR_1, LL_MULTICAST_ADDR_2, LWIP_ASSERT, LWIP_DBG_LEVEL_SERIOUS, LWIP_DBG_TRACE, LWIP_DEBUGF, netif::netmask, NULL, pbuf::payload, and pbuf_header().

Referenced by ethernetif_init().

static err_t etharp_output_to_arp_index	(	struct netif *	netif,
		struct pbuf *	q,
		u8_t	arp_idx
	)

static

Just a small helper function that sends a pbuf to an ethernet address in the arp_table specified by the index 'arp_idx'.

References ARP_AGE_REREQUEST_USED, arp_table, ERR_OK, etharp_entry::ethaddr, etharp_request(), etharp_send_ip(), ETHARP_STATE_STABLE, ETHARP_STATE_STABLE_REREQUESTING, netif::hwaddr, LWIP_ASSERT, and etharp_entry::state.

Referenced by etharp_output().

err_t etharp_query	(	struct netif *	netif,
		ip_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.

References arp_table, ERR_ARG, ERR_MEM, ERR_OK, ETHARP_DEBUG, etharp_find_entry(), ETHARP_FLAG_TRY_HARD, etharp_request(), etharp_send_ip(), ETHARP_SET_HINT, ETHARP_STATE_EMPTY, ETHARP_STATE_PENDING, ETHARP_STATE_STABLE, ETHARP_STATS_INC, netif::hwaddr, if(), ip_addr_isany, ip_addr_isbroadcast, ip_addr_ismulticast, pbuf::len, LWIP_ASSERT, LWIP_DBG_TRACE, LWIP_DEBUGF, memp_malloc(), pbuf::next, NULL, pbuf_alloc(), pbuf_copy(), pbuf_free(), PBUF_RAM, PBUF_RAW, pbuf_ref(), PBUF_ROM, etharp_entry::q, S16_F, etharp_entry::state, pbuf::tot_len, and pbuf::type.

Referenced by etharp_output().

static err_t etharp_raw	(	struct netif *	netif,
		const struct eth_addr *	ethsrc_addr,
		const struct eth_addr *	ethdst_addr,
		const struct eth_addr *	hwsrc_addr,
		const ip_addr_t *	ipsrc_addr,
		const struct eth_addr *	hwdst_addr,
		const ip_addr_t *	ipdst_addr,
		const u16_t	opcode
	)

static

Send a raw ARP packet (opcode and all addresses can be modified)

Parameters

netif	the lwip network interface on which to send the ARP packet
ethsrc_addr	the source MAC address for the ethernet header
ethdst_addr	the destination MAC address for the ethernet header
hwsrc_addr	the source MAC address for the ARP protocol header
ipsrc_addr	the source IP address for the ARP protocol header
hwdst_addr	the destination MAC address for the ARP protocol header
ipdst_addr	the destination IP address for the ARP protocol header
opcode	the type of the ARP packet

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

References ERR_MEM, ERR_OK, ETHADDR16_COPY, ETHARP_DEBUG, ETHARP_HWADDR_LEN, ETHARP_STATS_INC, ETHTYPE_ARP, ETHTYPE_IP, htons, netif::hwaddr_len, HWTYPE_ETHERNET, ip_addr_islinklocal, IPADDR2_COPY, pbuf::len, netif::linkoutput, LWIP_ASSERT, LWIP_DBG_LEVEL_SERIOUS, LWIP_DBG_TRACE, LWIP_DEBUGF, NULL, pbuf::payload, pbuf_alloc(), pbuf_free(), PBUF_RAM, PBUF_RAW, PP_HTONS, SIZEOF_ETH_HDR, and SIZEOF_ETHARP_PACKET.

Referenced by etharp_request().

err_t etharp_request	(	struct netif *	netif,
		ip_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

References ARP_REQUEST, ETHARP_DEBUG, etharp_raw(), netif::hwaddr, netif::ip_addr, LWIP_DBG_TRACE, and LWIP_DEBUGF.

Referenced by etharp_output_to_arp_index(), and etharp_query().

static err_t etharp_send_ip	(	struct netif *	netif,
		struct pbuf *	p,
		struct eth_addr *	src,
		struct eth_addr *	dst
	)

static

Send an IP packet on the network using netif->linkoutput The ethernet header is filled in before sending.

netif the lwIP network interface on which to send the packet p the packet to send, p->payload pointing to the (uninitialized) ethernet header src the source MAC address to be copied into the ethernet header dst the destination MAC address to be copied into the ethernet header

Returns: ERR_OK if the packet was sent, any other err_t on failure

References ETHADDR16_COPY, ETHADDR32_COPY, ETHARP_DEBUG, ETHARP_HWADDR_LEN, ETHTYPE_IP, netif::hwaddr_len, netif::linkoutput, LWIP_ASSERT, LWIP_DBG_TRACE, LWIP_DEBUGF, pbuf::payload, and PP_HTONS.

Referenced by etharp_output(), etharp_output_to_arp_index(), etharp_query(), and etharp_update_arp_entry().

void etharp_tmr ( void )

Clears expired entries in the ARP table.

This function should be called every ETHARP_TMR_INTERVAL milliseconds (5 seconds), in order to expire entries in the ARP table.

References ARP_MAXAGE, ARP_MAXPENDING, arp_table, etharp_entry::ctime, ETHARP_DEBUG, etharp_free_entry(), ETHARP_STATE_EMPTY, ETHARP_STATE_PENDING, ETHARP_STATE_STABLE, ETHARP_STATE_STABLE_REREQUESTING, LWIP_DEBUGF, etharp_entry::state, and U16_F.

Referenced by arp_timer().

static err_t etharp_update_arp_entry	(	struct netif *	netif,
		ip_addr_t *	ipaddr,
		struct eth_addr *	ethaddr,
		u8_t	flags
	)

static

Update (or insert) a IP/MAC address pair in the ARP cache.

If a pending entry is resolved, any queued packets will be sent at this point.

Parameters

netif	netif related to this entry (used for NETIF_ADDRHINT)
ipaddr	IP address of the inserted ARP entry.
ethaddr	Ethernet address of the inserted ARP entry.
flags

See Also: definition of ETHARP_FLAG_*

Returns

ERR_OK Succesfully updated ARP cache.
ERR_MEM If we could not add a new ARP entry when ETHARP_FLAG_TRY_HARD was set.
ERR_ARG Non-unicast address given, those will not appear in ARP cache.

See Also: pbuf_free()

References arp_table, etharp_entry::ctime, ERR_ARG, ERR_OK, ERR_RTE, ETHADDR32_COPY, ETHARP_DEBUG, etharp_find_entry(), ETHARP_FLAG_FIND_ONLY, ETHARP_FLAG_TRY_HARD, etharp_free_entry(), ETHARP_HWADDR_LEN, etharp_send_ip(), ETHARP_STATE_STABLE, netif::hwaddr, netif::hwaddr_len, ip4_addr1_16, ip4_addr2_16, ip4_addr3_16, ip4_addr4_16, ip_addr_isany, ip_addr_isbroadcast, ip_addr_ismulticast, ip_route(), LWIP_ASSERT, LWIP_DBG_TRACE, LWIP_DEBUGF, memp_free(), etharp_entry::netif, pbuf::next, NULL, pbuf_free(), etharp_entry::q, S16_F, snmp_insert_arpidx_tree, etharp_entry::state, netif::state, U16_F, and X16_F.

Referenced by etharp_arp_input().

err_t ethernet_input	(	struct pbuf *	p,
		struct netif *	netif
	)

Process received ethernet frames.

Using this function instead of directly calling ip_input and passing ARP frames through etharp in ethernetif_input, the ARP cache is protected from concurrent access.

Parameters