这个实验主要是需要在linux中运行的，我的系统用的Ubuntu，mininet应该是必须要在linux中运行，可以快速搭建模拟网络的平台，推荐使用Ubuntu系统，版本号从14.04到最新的都可以，64位或者32位都行。如果物理机是windows系统的话，可以使用虚拟机方式安装 Linux系统，推荐使用VirtualBox虚拟机 。运行Mininet环境时需要root权限，Mininet脚本只能使用 Python2来解释运行

2.1.mininet安装

2.2 cmake安装

sudo apt install cmake

2.3 xterm安装

sudo apt install xterm

2.4 wireshark安装

sudo apt install wireshark

3.作业要求：(交换机转发实验)

4.C语言完成函数编写工作

附件展示：

4.1 iface_info_t *lookup_port(u8 mac[ETH_ALEN]);

mac.c中的方法

// lookup the mac address in mac_port table
// FDB中寻找目的地址+port是否存在？
iface_info_t *lookup_port(u8 mac[ETH_ALEN])
{
	// iface_info_t *iface = NULL;
	// fprintf(stdout, "TODO: implement this function please.\n");
	// return iface;
	
	iface_info_t *iface = NULL;
	mac_port_entry_t *entry,*q;
	for (int i = 0; i < HASH_8BITS; i++) {
		list_for_each_entry_safe(entry, q, &mac_port_map.hash_table[i], list) {
			int cmp = memcmp((void*)entry->mac,(void*)mac,sizeof(u8)*ETH_ALEN);   //ETH_ALEN==6
			if(cmp==0) return entry->iface;
		}
	}
	return iface;
}

4.2 void insert_mac_port(u8 mac[ETH_ALEN], iface_info_t *iface);

mac.c中的方法

// insert the mac -> iface mapping into mac_port table
//FDB插入packet源地址+port
void insert_mac_port(u8 mac[ETH_ALEN], iface_info_t *iface)
{
	// fprintf(stdout, "TODO: implement this function please.\n");'
	mac_port_entry_t *entry = malloc(sizeof(mac_port_entry_t));
	bzero(entry, sizeof(mac_port_entry_t));
	time_t now = time(NULL);
	entry->visited = now;
	memcpy(entry->mac,mac,sizeof(u8)*ETH_ALEN);
	// memcpy(entry->iface,iface,sizeof(iface_info_t));
	entry->iface=iface;
	list_add_tail(&entry->list,&mac_port_map.hash_table[0]);           //我加在第一张hash table可以？   为什么hash_table存储了所有的entry？
	
}

4.3 int sweep_aged_mac_port_entry();

mac.c中的方法

// sweeping mac_port table, remove the entry which has not been visited in the
// last 30 seconds.
int sweep_aged_mac_port_entry()
{
	// int n = 0;
	// fprintf(stdout, "TODO: implement this function please.\n");
	// return n;
	int n=0;
	mac_port_entry_t *entry, *q;
	time_t now = time(NULL);
	for (int i = 0; i < HASH_8BITS; i++) {
		list_for_each_entry_safe(entry,q, &mac_port_map.hash_table[i],list) {
			if((int)(now - entry->visited) >= MAC_PORT_TIMEOUT){
				n = entry->iface->index;
				list_delete_entry(&entry->list);
				free(entry);
				return n;
			}
		}
	}
	return n;
}

4.4 void broadcast_packet(iface_info_t iface, const char packet, int len);

packet.c中的方法

// broadcast the packet among all the interfaces except the one receiving the
// packet, and free memory of the packet
//在所有的接口中广播(不包含当前接口)
void broadcast_packet(iface_info_t *iface, char *packet, int len)
{
	iface_info_t *tx_iface = NULL;
	list_for_each_entry(tx_iface, &instance->iface_list, list) {
		if (tx_iface->index == iface->index)
			continue;

		iface_send_packet(tx_iface, packet, len);
	}
}

4.5 void handle_packet(iface_info_t iface, char packet, int len);

main.c中的方法

// handle packet
// 1. if the dest mac address is found in mac_port table, forward it; otherwise, 
// broadcast it.
// 2. put the src mac -> iface mapping into mac hash table.
void handle_packet(iface_info_t *iface, char *packet, int len)
{
	//得到头部信息
	struct ether_header *eh = (struct ether_header *)packet;
	//fdb中寻找目的地址mac
	iface_info_t *tx_iface = lookup_port(eh->ether_dhost);
	if (tx_iface) {
		iface_send_packet(tx_iface, packet, len);
	}
	else {
		broadcast_packet(iface, packet, len);
	}
	//存入源mac+port
	if (!lookup_port(eh->ether_shost)) {
		insert_mac_port(eh->ether_shost, iface);
	}
}