Problem understanding SNMP configuration

[huyan]

Hello, 

I have problem understanding this SNMP configuration. The commands are below: 

ALS1(config)# access-list 1 permit 192.168.1.0 0.0.0.255  

ALS1(config)# snmp-server community LEVEL1 ro 1     #Line 2

ALS1(config)# snmp-server enable traps vtp     

ALS1(config)#snmp-server host 10.1.1.253 traps version 2c LEVEL1 vtp       

To my understanding, the ALS1 is the monitored device and it will send SNMP messages related to VTP to host 10.1.1.253

The thing that I can't understand is line 2, some tutorials online do not use access-list. Their command is just like this : 

ALS1(config)# snmp-server community LEVEL1 ro  

However, in the book I am reading, the author creates access-list 1 and use it with community string like this.

ALS1(config)# snmp-server community LEVEL1 ro 1

I don't know the role of the subnet  192.168.1.0 0.0.0.255 in this configuration. Please help. 

I appreciate your help!

Best, 

Huyan.

[Dennis Mink]

The access list only allows snmp access from the /24 subnet you defined.

[huyan]

Thank you for your answer.
Please correct that I am wrong:

ALS1 is the SNMP Agent
Host 10.1.1.253 is SNMP Manager
Subnet 192.168.1.0 0.0.0.255: it's for SNMP access from. What is the name/keyword for this components so I will search and read more online?