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It feels a bit like using a default password. You might initially view the use of the default community string "public" as a security hole. It's quite common for users to never change from this default, allowing all SNMP agents in the network to communicate with the (usually single) manager.
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The default SNMP community string is "public" for the vast majority of devices. A receiving device will discard any message if that string doesn't match its own. Devices (management stations called "managers" and their managed devices called "agents") include a small text "community string" with each message. Fortunately, it's really quite simple.Īn SNMP community is something like a VLAN in the SNMP layer. SNMP is community-based, so there's the concept of "community string" that needs to be understood. Note: Agents use UDP 161, while the manager uses UDP 162. Therefore, typically, SNMP uses UDP port 161 and UDP port 162. UDP is actually better suited for repetitive, low-priority functions like alarm monitoring. UDP is faster than TCP because it does not order packets (which can be done by the application layer), and it is a connection-less protocol. While UDP may not have all the functionality of TCP, this actually makes it better for some applications.
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While TCP can be used for SNMP, it was originally designed with UDP transport only. TCP is relatively heavy, meaning it requires three packets to set up a connection before user data can be sent. TCP is connection based, meaning that one program is connected to another program and they send messages across the internet to each other.