代码版本：

通告处理

VRRP 调度器处理传入的 VRRP 通告，并根据实例的当前状态对其进行处理：

代码流程

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vrrp_read_dispatcher_thread
    vrrp_dispatcher_read
        /* read & affect received buffer */
        read(fd, vrrp_buffer, VRRP_PACKET_TEMP_LEN);

        /* Searching for matching instance */
        vrrp = vrrp_index_lookup(hd->vrid, fd);

        /* Run the FSM handler */
        prev_state = vrrp->state;
        VRRP_FSM_READ(vrrp, vrrp_buffer, len);
            /* MASTER */
            vrrp_leave_master
                vrrp_state_master_rx
                    /* Process the incoming packet */
                    ret = vrrp_check_packet(vrrp, buf, buflen);

                    if (Lower priority) {
                      vrrp_send_adv(vrrp, vrrp->priority);
                      vrrp_send_gratuitous_arp(vrrp);
                      return 0;
                    }
                    else {
                      vrrp->ms_down_timer =
                          3 * vrrp->adver_int + VRRP_TIMER_SKEW(vrrp);
                      vrrp->wantstate = VRRP_STATE_BACK;
                      vrrp->state = VRRP_STATE_BACK;
                      return 1;
                    }
            /* BACKUP */
            vrrp_backup
                vrrp_state_backup
                    if(Higher priority)
                        vrrp->ms_down_timer =
		                      3 * vrrp->adver_int + VRRP_TIMER_SKEW(vrrp);
                    else
                        vrrp->wantstate = VRRP_STATE_GOTO_MASTER;
		                    vrrp_send_adv(vrrp, vrrp->priority);

vrrp_send_adv

  1. VRRP 协议报文封装在 IP 报文中，发送到分配给 VRRP 的 IP 组播地址
  2. 在IP 报文头中
  • 源地址为发送报文接口的主 IP 地址
  • 目的地址为 224.0.0.18
  • TTL 必须是 255。（VRRP 路由器会丢弃 TTL 不等于 255 的 VRRP 协议报文）
  • 协议号是 112
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/* send VRRP advertissement */
vrrp_send_adv
    /* build VRRP packet */
    vrrp_build_pkt(vrrp, prio)
        /* build IP header */
        vrrp_build_ip
            ip->ttl = VRRP_IP_TTL;
            ip->protocol =
              (vrrp->auth_type == VRRP_AUTH_AH) ? IPPROTO_IPSEC_AH : IPPROTO_VRRP;
            ip->saddr = VRRP_PKT_SADDR(vrrp);
            ip->daddr = htonl(INADDR_VRRP_GROUP);
            /* checksum must be done last */
            ip->check = in_csum((u_short *) ip, ip->ihl * 4, 0);
        /* build the vrrp header */
        vrrp_build_vrrp(vrrp, prio, vrrp->send_buffer, vrrp->send_buffer_size)
keepalived

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