therearedifferentwaystoper（2017年上半年信信息安全工程师上午综合知识真题解析）
There are different ways to perform IP based DoS Attacks. The most common IP based DoS attack is that an attacker sends an extensive amount of connection establishment （1）(e.g. TCP SYN requests) to establish hanging connections with the controller or a DPS. Such a way, the attacker can consume the network resources which should be available for legitimate users. In other （2）, the attacker inserts a large amount of （3）packets to the data plane by spoofing all or part of the header fields with random values. These incoming packets will trigger table-misses and send lots of packet-in flow request messages to the network controller to saturate the controller resources. In some cases, an （4）who gains access to DPS can artificially generate lots of random packet-in flow request messages to saturate the control channel and the controller resources. Moreover, the lack of diversity among DPSs fuels fuels the fast propagation of such attacks.
Legacy mobile backhaul devices are inherently protected against the propagation of attacks due to complex and vendor specific equipment. Moreover, legacy backhaul devices do not require frequent communication with core control devices in a manner similar to DPSs communicating with the centralized controller. These features minimize both the impact and propagation of DoS attacks. Moreover, the legacy backhaul devices are controlled as a joint effort of multiple network element. For instance, a single Long Term Evilution（LTE）eNodeB is connected up to 32 MMEs. Therefore, DoS/DDoS attack on a single core element will not terminate the entire operation of a backhaul device（5）the net work.
（2）A.methods B、cases C、hands D、sections
（3）A.bad B、real C、fake D、new
（4）A.user B、administrator C、editor D、attacker
（5）A.or B、of C、in D、to