[单项选择]

网管人员在监测网络运行状态时，发现下列现象：服务器上有大量的TCP连接，收到了大量源地址各异、用途不明的数据包；服务器收到大量的ARP报文。网管人员的判断是 (54) ，针对前一现象将采取的措施是 (55) ，针对后一现象可能采取的措施是 (56) 。

（54）处填（）。
A. 受到了DoS攻击和ARP攻击
B. 受到了DDoS攻击和ARP欺骗攻击
C. 受到了漏洞攻击和DNS欺骗攻击
D. 受到了DDoS攻击和DNS欺骗攻击

Each machine supporting TCP has a TCP transport entity, either a library procedure, a user process, or part of the kernel. In all case, it manages TCP streams and （） to the IP layer.A TCP （） accepts user data streams from local process, breaks them into pieces not exceeding 64KB, and sends each piece as a separate IP （） . When datagrams containing TCP data arrive at a machine, they are given to the TCP entity,which reconstructs the original byte streams. The IP layer gives no guarantee that datagrams will be delivered properly, so it is up to TCP to time out and （） them as need be. Datagrams do arrive may well do so in the wrong order, it is also up to TCP to （） them into messages in the proper sequence.