/* 发送一个ICMP差错报文 */
static void
icmp_send_response(struct pbuf *p, u8_t type, u8_t code)
{
struct pbuf *q;
struct ip_hdr *iphdr;
/* we can use the echo header here */
/* 用回显请求的首部描述差错报文首部 */
struct icmp_echo_hdr *icmphdr;
/* ICMP header + IP header + 8 bytes of data */
/* 在IP层申请一个pbuf，会自动预留IP首部和以太网帧首部，
* 申请的大小是回显请求首部 + 引起差错的IP数据报首部大小 + IP数据报载荷的前8字节
*/
q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
PBUF_RAM);
if (q == NULL) {
/* 申请失败，则返回 */
LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
return;
}
LWIP_ASSERT("check that first pbuf can hold icmp message",
(q->len >= (sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));
/* 指向引起差错的IP数据报 */
iphdr = p->payload;
LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
LWIP_DEBUGF(ICMP_DEBUG, (" to "));
ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
LWIP_DEBUGF(ICMP_DEBUG, ("\n"));
/* 指向ICMP报文首部 */
icmphdr = q->payload;
/* 填写类型字段 */
icmphdr->type = type;
/* 填写代码字段 */
icmphdr->code = code;
/* ICMP首部第4-7字节填0 */
icmphdr->id = 0;
icmphdr->seqno = 0;
/* copy fields from original packet */
/* 复制引起差错的IP数据报首部+8字节到ICMP数据字段 */
SMEMCPY((u8_t *)q->payload + sizeof(struct icmp_echo_hdr), (u8_t *)p->payload,
IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);
/* calculate checksum */
/* 计算并填写校验和 */
icmphdr->chksum = 0;
icmphdr->chksum = inet_chksum(icmphdr, q->len);
ICMP_STATS_INC(icmp.xmit);
/* increase number of messages attempted to send */
snmp_inc_icmpoutmsgs();
/* increase number of destination unreachable messages attempted to send */
snmp_inc_icmpouttimeexcds();
/* 调用IP层函数输出ICMP报文 */
ip_output(q, NULL, &(iphdr->src), ICMP_TTL, 0, IP_PROTO_ICMP);
/* 发送完成，释放申请的ICMP用的pbuf */
pbuf_free(q);
}
void
icmp_time_exceeded(struct pbuf *p, enum icmp_te_type t)
{
struct pbuf *q;
struct ip_hdr *iphdr;
struct icmp_te_hdr *tehdr;
q = pbuf_alloc(PBUF_IP, 8 + IP_HLEN + 8, PBUF_RAM);
iphdr = p->payload;
LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
LWIP_DEBUGF(ICMP_DEBUG, (" to "));
ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
LWIP_DEBUGF(ICMP_DEBUG, ("\n"));
tehdr = q->payload;
ICMPH_TYPE_SET(tehdr, ICMP_TE);
ICMPH_CODE_SET(tehdr, t);
/* copy fields from original packet */
memcpy((u8_t *)q->payload + 8, (u8_t *)p->payload, IP_HLEN + 8);
/* calculate checksum */
tehdr->chksum = 0;
tehdr->chksum = inet_chksum(tehdr, q->len);
ICMP_STATS_INC(icmp.xmit);
/* increase number of messages attempted to send */
snmp_inc_icmpoutmsgs();
/* increase number of destination unreachable messages attempted to send */
snmp_inc_icmpouttimeexcds();
ip_output(q, NULL, &(iphdr->src),
ICMP_TTL, 0, IP_PROTO_ICMP);
pbuf_free(q);
}
static struct netif *
ip_forward(struct pbuf *p, struct ip_hdr *iphdr, struct netif *inp)
{
struct netif *netif;
PERF_START;
/* Find network interface where to forward this IP packet to. */
netif = ip_route((struct ip_addr *)&(iphdr->dest));
if (netif == NULL) {
LWIP_DEBUGF(IP_DEBUG, ("ip_forward: no forwarding route for 0x%"X32_F" found\n",
iphdr->dest.addr));
snmp_inc_ipnoroutes();
return (struct netif *)NULL;
}
/* Do not forward packets onto the same network interface on which
* they arrived. */
if (netif == inp) {
LWIP_DEBUGF(IP_DEBUG, ("ip_forward: not bouncing packets back on incoming interface.\n"));
snmp_inc_ipnoroutes();
return (struct netif *)NULL;
}
/* decrement TTL */
IPH_TTL_SET(iphdr, IPH_TTL(iphdr) - 1);
/* send ICMP if TTL == 0 */
if (IPH_TTL(iphdr) == 0) {
/* Don't send ICMP messages in response to ICMP messages */
if (IPH_PROTO(iphdr) != IP_PROTO_ICMP) {
icmp_time_exceeded(p, ICMP_TE_TTL);
snmp_inc_icmpouttimeexcds();
}
return (struct netif *)NULL;
}
/* Incrementally update the IP checksum. */
if (IPH_CHKSUM(iphdr) >= htons(0xffff - 0x100)) {
IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100) + 1);
} else {
IPH_CHKSUM_SET(iphdr, IPH_CHKSUM(iphdr) + htons(0x100));
}
LWIP_DEBUGF(IP_DEBUG, ("ip_forward: forwarding packet to 0x%"X32_F"\n",
iphdr->dest.addr));
IP_STATS_INC(ip.fw);
IP_STATS_INC(ip.xmit);
snmp_inc_ipforwdatagrams();
PERF_STOP("ip_forward");
/* transmit pbuf on chosen interface */
netif->output(netif, p, (struct ip_addr *)&(iphdr->dest));
return netif;
}
/**
* Send an icmp packet in response to an incoming packet.
*
* @param p the input packet for which the 'unreachable' should be sent,
* p->payload pointing to the IP header
* @param type Type of the ICMP header
* @param code Code of the ICMP header
*/
static void icmp_send_response(struct pbuf *p, u8_t type, u8_t code)
{
struct pbuf *q;
struct ip_hdr *iphdr;
/* we can use the echo header here */
struct icmp_echo_hdr *icmphdr;
/* ICMP header + IP header + 8 bytes of data */
q =
pbuf_alloc(PBUF_IP,
sizeof(struct icmp_echo_hdr) + IP_HLEN +
ICMP_DEST_UNREACH_DATASIZE, PBUF_RAM);
if (q == NULL) {
LWIP_DEBUGF(ICMP_DEBUG,
("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
return;
}
LWIP_ASSERT("check that first pbuf can hold icmp message",
(q->len >=
(sizeof(struct icmp_echo_hdr) + IP_HLEN +
ICMP_DEST_UNREACH_DATASIZE)));
iphdr = p->payload;
LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
LWIP_DEBUGF(ICMP_DEBUG, (" to "));
ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
LWIP_DEBUGF(ICMP_DEBUG, ("\n"));
icmphdr = q->payload;
icmphdr->type = type;
icmphdr->code = code;
icmphdr->id = 0;
icmphdr->seqno = 0;
/* copy fields from original packet */
SMEMCPY((u8_t *) q->payload + sizeof(struct icmp_echo_hdr),
(u8_t *) p->payload, IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);
/* calculate checksum */
icmphdr->chksum = 0;
icmphdr->chksum = inet_chksum(icmphdr, q->len);
ICMP_STATS_INC(icmp.xmit);
/* increase number of messages attempted to send */
snmp_inc_icmpoutmsgs();
/* increase number of destination unreachable messages attempted to send */
snmp_inc_icmpouttimeexcds();
ip_output(q, NULL, &(iphdr->src), ICMP_TTL, 0, IP_PROTO_ICMP);
pbuf_free(q);
}
/**
* Send an icmp packet in response to an incoming packet.
*
* @param p the input packet for which the 'unreachable' should be sent,
* p->payload pointing to the IP header
* @param type Type of the ICMP header
* @param code Code of the ICMP header
*/
static void ICACHE_FLASH_ATTR
icmp_send_response(struct pbuf *p, u8_t type, u8_t code)
{
struct pbuf *q;
struct ip_hdr *iphdr;
/* we can use the echo header here */
struct icmp_echo_hdr *icmphdr;
ip_addr_t iphdr_src;
/* ICMP header + IP header + 8 bytes of data */
//为差错报文申请pbuf空间，pbuf中预留IP首部和以太网首部空间，pbuf数据区
//长度=差错报文首部+差错报文数据长度(IP首部长度+8)
q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
PBUF_RAM);
if (q == NULL) {//失败，返回
LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
return;
}
LWIP_ASSERT("check that first pbuf can hold icmp message",
(q->len >= (sizeof(struct icmp_echo_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));
iphdr = (struct ip_hdr *)p->payload;//指向引起差错的IP数据包首部
LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
LWIP_DEBUGF(ICMP_DEBUG, (" to "));
ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
LWIP_DEBUGF(ICMP_DEBUG, ("\n"));
icmphdr = (struct icmp_echo_hdr *)q->payload;//指向差错报文首部
icmphdr->type = type;//填写类型字段
icmphdr->code = code;//填写代码字段
icmphdr->id = 0;//对于目的不可达和数据报超时
icmphdr->seqno = 0;//报文，首部剩余的4个字节都为0
/* copy fields from original packet 将引起差错的IP数据报的IP首部+8字节数据拷贝到差错报文数据区*/
SMEMCPY((u8_t *)q->payload + sizeof(struct icmp_echo_hdr), (u8_t *)p->payload,
IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);
/* calculate checksum */
icmphdr->chksum = 0;//报文校验和字段清0
icmphdr->chksum = inet_chksum(icmphdr, q->len);//计算填写校验和
ICMP_STATS_INC(icmp.xmit);
/* increase number of messages attempted to send */
snmp_inc_icmpoutmsgs();
/* increase number of destination unreachable messages attempted to send */
snmp_inc_icmpouttimeexcds();
ip_addr_copy(iphdr_src, iphdr->src);
ip_output(q, NULL, &iphdr_src, ICMP_TTL, 0, IP_PROTO_ICMP);//调用IP层函数输出ICMP报文
pbuf_free(q);
}
/**
* Send a 'time exceeded' packet, called from ip_forward() if TTL is 0.
*
* @param p the input packet for which the 'time exceeded' should be sent,
* p->payload pointing to the IP header
* @param t type of the 'time exceeded' packet
*/
void
icmp_time_exceeded(struct pbuf *p, enum icmp_te_type t)
{
struct pbuf *q;
struct ip_hdr *iphdr;
struct icmp_te_hdr *tehdr;
/* ICMP header + IP header + 8 bytes of data */
q = pbuf_alloc(PBUF_IP, sizeof(struct icmp_dur_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE,
PBUF_RAM);
if (q == NULL) {
LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMP packet.\n"));
return;
}
LWIP_ASSERT("check that first pbuf can hold icmp message",
(q->len >= (sizeof(struct icmp_dur_hdr) + IP_HLEN + ICMP_DEST_UNREACH_DATASIZE)));
iphdr = (struct ip_hdr *) p->payload;
LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded from "));
ip_addr_debug_print(ICMP_DEBUG, &(iphdr->src));
LWIP_DEBUGF(ICMP_DEBUG, (" to "));
ip_addr_debug_print(ICMP_DEBUG, &(iphdr->dest));
LWIP_DEBUGF(ICMP_DEBUG, ("\n"));
tehdr = (struct icmp_te_hdr *) q->payload;
ICMPH_TYPE_SET(tehdr, ICMP_TE);
ICMPH_CODE_SET(tehdr, t);
/* copy fields from original packet */
SMEMCPY((u8_t *)q->payload + sizeof(struct icmp_dur_hdr), (u8_t *)p->payload,
IP_HLEN + ICMP_DEST_UNREACH_DATASIZE);
/* calculate checksum */
tehdr->chksum = 0;
tehdr->chksum = inet_chksum(tehdr, q->len);
ICMP_STATS_INC(icmp.xmit);
/* increase number of messages attempted to send */
snmp_inc_icmpoutmsgs();
/* increase number of destination unreachable messages attempted to send */
snmp_inc_icmpouttimeexcds();
ip_output(q, NULL, &(iphdr->src), ICMP_TTL, 0, IP_PROTO_ICMP);
pbuf_free(q);
}
