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Packet sender older versions4/30/2023 ![]() ![]() SNMP (other than SNMPv3) is unencrypted, so a "secret" community string is easy to learn. Even though you can obstruct unauthorized SNMP traffic by using a non-standard community string, that's not much of an obstacle for a determined intruder. It's probably a bigger problem, though, to think the community string offers much security at all. Even the word "public" describes the people you need to keep out of your secured system. 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. ![]() 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. 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. ![]()
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