SNMP

Andrew Kirch — Tue, 24 Jan 2017 14:28:55 +0000

How would you find out how much RAM is free on your Linux desktop? That's a really easy question with a lot of answers—free, any of the implementations of top and Glances all are valid responses. How would you find out how much RAM is free on 200 Linux instances, which are running on a mixture of real and virtual hardware, in dozens of physical locations spread out around the globe? That's a much bigger problem, and there is a tool to make the job easier. However, the lack of upkeep on the standards and lack of development support for the Linux implementation are resulting in proprietary standards creeping in where there once was a more open standard.

SNMP (Simple Network Management Protocol) was designed in 1990 to read and write structured data on devices attached to a network, such as how much free RAM there is. Yes, and this is important, the M in SNMP really does stand for "Management", not "Monitoring". Although SNMP is usually used to request operational status information, the SNMP "write" functionality can be used to change the configuration on remote devices. Given the lack of security and authentication in the SNMP protocol, SNMP "write" functionality almost always is disabled on the modern internet, and I will not be discussing it here.

History of SNMP

The original IETF (Internet Engineering Task Force) RFC (Request for Comments) standard for SNMP v1 was published by the IETF in 1990. SNMP v2 was published in 1994–1996 as a series of RFCs and included the first effort to secure SNMP. This effort proved unpopular due to the load it placed on network hardware, which, at the time, had very low performance CPUs. This performance issue exists today and still can cause problems for administrators attempting to secure SNMP. Due to the performance problems, SNMP v2c (SNMP v2 with SNMP v1 communities) became the standard. Concurrently with the release of SNMPv2c, the public began to access the internet, and during the next decade, security would become a serious problem with SNMP since SNMP v2c was entirely unencrypted. SNMPv3 came along in 2003 and added TLS to the previous implementation of SNMP v2c. If all of this seems a bit complicated and unnecessary, it's important to know that many implementations of SNMP still ship with support for SNMP v1, v2c and SNMP v3. This means you're likely to see all of them in the wild.

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