This file defines an ARP cache (sr_arpcache), which is made of two structures: an ARP request queue (sr_arpreq), and ARP cache entries (sr_arpentry). More...

#include <inttypes.h>
#include <time.h>
#include <pthread.h>
#include "sr_if.h"

Include dependency graph for sr_arpcache.h:

This graph shows which files directly or indirectly include this file:

Go to the source code of this file.

Classes
struct	sr_packet
	A packet queued, waiting for the resolution of an sr_arpreq. More...

struct	sr_arpentry
	An entry in the ARP cache. More...

struct	sr_arpreq
	An outstanding ARP request with queued packets waiting on the response. More...

struct	sr_arpcache
	An ARP cache which tracks IP/MAC mappings, as well as outstanding ARP requests. More...

Macros
#define	SR_ARPCACHE_SZ 100

#define	SR_ARPCACHE_TO 15.0

Functions
struct sr_arpentry *	sr_arpcache_lookup (struct sr_arpcache *cache, uint32_t ip)
	Checks if an IP->MAC mapping is in the cache. More...

struct sr_arpreq *	sr_arpcache_queuereq (struct sr_arpcache cache, uint32_t ip, uint8_t packet, unsigned int packet_len, char *iface)
	Adds an ARP request to the ARP request queue. More...

struct sr_arpreq *	sr_arpcache_insert (struct sr_arpcache cache, unsigned char mac, uint32_t ip)
	Inserts an ARP cache entry. More...

void	sr_arpreq_destroy (struct sr_arpcache cache, struct sr_arpreq entry)
	Frees all memory associated with this arp request entry. More...

void	sr_arpcache_dump (struct sr_arpcache *cache)
	Prints out the ARP table. More...

int	sr_arpcache_init (struct sr_arpcache *cache)
	sr_arpcache constructor, you shouldn't need to call this, the starter code calls it for you.

int	sr_arpcache_destroy (struct sr_arpcache *cache)
	sr_arpcache destructor, you shouldn't need to call this, the starter code calls it for you.

void *	sr_arpcache_timeout (void *cache_ptr)
	A cleanup command which clears out ARP cache entries every 15 seconds, you shouldn't need to call this, it is called on a separte thread by the starter code for you.

Detailed Description

This file defines an ARP cache (sr_arpcache), which is made of two structures: an ARP request queue (sr_arpreq), and ARP cache entries (sr_arpentry).

Here, we present pseudocode for use of these structures.
The outline for sending a packet using the ARP cache is as follows:

// When sending packet to next_hop_ip
entry = arpcache_lookup(next_hop_ip)
if entry:
    use next_hop_ip->mac mapping in entry to send the packet
    free entry
else:
    req = arpcache_queuereq(next_hop_ip, packet, len)
    handle_arpreq(req)

The handle_arpreq() function is a function you should write, and it should handle sending ARP requests if necessary:

function handle_arpreq(req):
    if difftime(now, req->sent) > 1.0
        if req->times_sent >= 5:
            send icmp host unreachable to source addr of all pkts waiting
              on this request
            arpreq_destroy(req)
        else:
            send arp request
            req->sent = now
            req->times_sent++

The ARP reply processing code should move entries from the ARP request queue to the ARP cache:

// When servicing an arp reply that gives us an IP->MAC mapping
req = arpcache_insert(ip, mac)
if req:
    send all packets on the req->packets linked list
    arpreq_destroy(req)

Since handle_arpreq as defined in the comments above could destroy your current request, make sure to save the next pointer before calling handle_arpreq when traversing through the ARP requests linked list.

Function Documentation

◆ sr_arpcache_dump()

void sr_arpcache_dump ( struct sr_arpcache * cache )

Prints out the ARP table.

◆ sr_arpcache_insert()

struct sr_arpreq* sr_arpcache_insert	(	struct sr_arpcache *	cache,
		unsigned char *	mac,
		uint32_t	ip
	)

Inserts an ARP cache entry.

This method performs two functions: 1) Looks up this IP in the request queue. If it is found, returns a pointer to the sr_arpreq with this IP. Otherwise, returns NULL. 2) Inserts this IP to MAC mapping in the cache, and marks it valid.

◆ sr_arpcache_lookup()

struct sr_arpentry* sr_arpcache_lookup	(	struct sr_arpcache *	cache,
		uint32_t	ip
	)

Checks if an IP->MAC mapping is in the cache.

IP is in network byte order. You must free the returned structure if it is not NULL.

◆ sr_arpcache_queuereq()

struct sr_arpreq* sr_arpcache_queuereq	(	struct sr_arpcache *	cache,
		uint32_t	ip,
		uint8_t *	packet,
		unsigned int	packet_len,
		char *	iface
	)

Adds an ARP request to the ARP request queue.

If the request is already on the queue, adds the packet to the linked list of packets for this sr_arpreq that corresponds to this ARP request. The packet argument should not be freed by the caller.

A pointer to the ARP request is returned; it should be freed. The caller can remove the ARP request from the queue by calling sr_arpreq_destroy.

◆ sr_arpreq_destroy()

void sr_arpreq_destroy	(	struct sr_arpcache *	cache,
		struct sr_arpreq *	entry
	)

Frees all memory associated with this arp request entry.

If this arp request entry is on the arp request queue, it is removed from the queue.

Classes

Macros