为方便广大考生考后估分对答案，希赛网特向广大学员和网友搜集整理了相关真题信息，供大家参考。收集完整2021年上半年软考网络工程师真题答案后，希赛网的老师也将在考后第一时间进行真题答案解析，敬请广大考友考后积极关注。

现在要推荐给大家的是文字版2021年上半年软考网络工程师考试上午真题及答案解析71-75题。

●Network Addres Translation(NAT) is an Internet standard that enbles a local-area network to use one set of IP addresses for internet traffic and another set of (71) IP addresses for external traffic. The main use of NAT is to limit the number of public IP addresses that an organization or company must use, for both economy and (72) purposes. NAT remaps an IP address space into another by modifying network address information in the (73) header of packets while they are in transit across a traffic routing device. It has become an essential tool in conserving global address space in the face of (74) address exhaustion. When a packet traverses outside the local network, NAT converts the private IP address to a public IP address. If NAT runs out of public addresses，the packets will be dropped and (75)"host unreachable"packets will be sent.

(71) A. local

B. private

c. public

D. dynamic

(72) A. political

B. fairness

c. efficiency

D. security

(73) A.MAC

B. IP

c.TCP

D. UDP

(74) A. IPv4

B. IPv6

c. MAC

D. logical

(75) A. BGP

B. IGMP

c. ICMP

D. SNMP