What does a network administrator do

The main work of a network administrator is to keep network of organization operating and up to date. So any company or organization with multiple computers needs network administrator (or admin) to connect and coordinate different computers or systems. 

Duties perform by Network administrator :

1. Detect failure of interface card at host or router :
   A router or host has more than one interface to connect with Internet, and there is chance that the interface by which we are connected goes down. So to impress and attract user, network administration can detect the problem and inform user about it by using some network management tools. 
2. Host monitoring :
   Network administrator regularly monitors all host inside its network and check all host are working fine or not. 
   And also it can block particular host to use particular services (like youtube etc) by blocking that port number on the host side. 
3. Adding or removing host from the network :
   Network administrator can add or remove host from network, and it can also configure subnet mask for host such that host will in network but it will act as it is in some other network. And all the packets send to that packet goes first to gateway and gateway will transfer that packet to that host. 
4. Monitoring traffic :
   Since the standard router has only physical layer, data link layer and network layer, so it can only perform routing(i.e, making routing table, by help of Link State Routing algorithm, it decide route) and for routing it LSR does not detect congestion (traffic) on certain route. So is too many packets follow the same route there will congestion on that route. 
5. Detecting rapid changes in routing tables :
   When network administrator configures router improperly then it will not work correctly and changes routes very rapidly and at last goes down. And from saving router going down administrator will discover error by him or her self. 
6. Monitor for Service Level Agreement (SLA) :
   SLAs are the contract that defines specific performance metrics. Verizon and Sprint are just two of the many network provider that guarantee SLAs to their customers. These SLAs include service availability, latency, throughput, and outage notification requirements. 
7. Installing, Repairing and Updating software and hardware :
   It is the duty of network administrator to install new software or hardware into network if any part of network (like router, cable or switch etc) not working properly that administrator will replace or update that component of network. 
8. Updating security systems and security authorization :
   Intrusion detection and providing extra security is very crucial duty of network administration. There are several systems that try to hack or down server or any system into the network. For example, Any external host tries to down server by sending to many ping (echo) ICMP packets, and this led to decrease in the performance. Network administrator can easily detect such action and block that IP address.