Reproduced LWIP's IP/MAC address conflict detection

from:http://blog.csdn.net/tianjueyiyi/article/details/51097447

LWIP is a lightweight TCP/IP stack, which is lightweight because the author concentrates the main functions into a relatively simple protocol stack, which is mainly used in rom/ram rare environments. it is because of the light weight, simple, so usually a lot of things for granted, we will feel that in this can also be achieved, in fact, otherwise, people who have used lwIP will feel. If a situation, you set the Ip/mac and other devices in the network conflict, at this time can not detect, but also find out what is the reason, always link will be broken for no reason. here, in response to the problem of conflict, proposed a solution, welcome to correct. First, you need to understand what gratuitous ARP is. Interested can Baidu a bit, here I summarize. When the device access network, you need to send a message to ask other devices, "I sent this IP, who has?" ”。 If this IP is present in the network, it will reply; it is using gratuitous ARP to judge its reply, if the received response or reply, the IP is the same as the device itself, it is marked as an IP conflict. Mac conflicts in the same vein. in lwIP, improvements can be made to detect Mac and IP collisions in the following areas. The main part of the code is posted below.

Etharp_arp_input (struct netif *netif, struct eth_addr *ethaddr, struct pbuf *p) {

...

Case Pp_htons (arp_request):
if (ip_addr_cmp (&sipaddr, & (NETIF->IP_ADDR))) {
Etharperror |= duplicate_ip;
}
if ((hdr->shwaddr.addr[0] = = netif->hwaddr[0]) &&
(hdr->shwaddr.addr[1] = = netif->hwaddr[1]) &&
(hdr->shwaddr.addr[2] = = netif->hwaddr[2]) &&
(Hdr->shwaddr.addr[3] = = netif->hwaddr[3]) &&
(Hdr->shwaddr.addr[4] = = netif->hwaddr[4]) &&
(Hdr->shwaddr.addr[5] = = netif->hwaddr[5])) {
Etharperror |= Duplicate_mac;
}

...

Case Pp_htons (arp_reply):
if (ip_addr_cmp (&sipaddr, & (NETIF->IP_ADDR))) {
Etharperror |= duplicate_ip;
}
if ((hdr->shwaddr.addr[0] = = netif->hwaddr[0]) &&
(hdr->shwaddr.addr[1] = = netif->hwaddr[1]) &&
(hdr->shwaddr.addr[2] = = netif->hwaddr[2]) &&
(Hdr->shwaddr.addr[3] = = netif->hwaddr[3]) &&
(Hdr->shwaddr.addr[4] = = netif->hwaddr[4]) &&
(Hdr->shwaddr.addr[5] = = netif->hwaddr[5])) {
Etharperror |= Duplicate_mac;
}

...

In other places of use just judge the Etharperror variable to see if there is a conflict. Because gratuitous ARP is emitted when the machine is initialized when it is connected to the network, there is no need to worry about whether or not a conflict has been detected while judging the variable.

Reproduced LWIP's IP/MAC address conflict detection