WEBVTT 0:00:02.820000 --> 0:00:07.800000 Hello and welcome to this video titled SNMP components. 0:00:07.800000 --> 0:00:11.620000 In this video I'm going to talk about the components and architecture 0:00:11.620000 --> 0:00:16.460000 that make up SNMP and we'll also briefly look at some of the main popular 0:00:16.460000 --> 0:00:18.800000 SNMP message types. 0:00:18.800000 --> 0:00:23.060000 So let's start by talking about SNMP components. 0:00:23.060000 --> 0:00:26.820000 So whenever you learn of any new protocol, regardless of what layer of 0:00:26.820000 --> 0:00:31.060000 the OSI model it lives at, the first thing you have to know are what are 0:00:31.060000 --> 0:00:35.060000 the devices that implement this protocol and do these devices play a special 0:00:35.060000 --> 0:00:38.840000 role? Is there something that they do that other devices working with 0:00:38.840000 --> 0:00:41.360000 the exact same protocol don't do? 0:00:41.360000 --> 0:00:44.000000 And then clearly there's probably a bunch of acronyms and terminology 0:00:44.000000 --> 0:00:47.160000 you have to get used to as well with that protocol. 0:00:47.160000 --> 0:00:49.060000 Same thing is here as well. 0:00:49.060000 --> 0:00:54.040000 So with SNMP it's really a client-server architecture. 0:00:54.040000 --> 0:00:56.720000 Just like so many network protocols are. 0:00:56.720000 --> 0:01:01.120000 Now in the terms of SNMP things are a little bit reversed though in that 0:01:01.120000 --> 0:01:05.420000 you will have a server which we call the SNMP manager. 0:01:05.420000 --> 0:01:07.200000 Now that's going to be an SNMP server. 0:01:07.200000 --> 0:01:11.280000 It could be a Linux or a Windows server and it's running some sort of 0:01:11.280000 --> 0:01:14.120000 network management station software on it. 0:01:14.120000 --> 0:01:19.020000 And there's lots of software out there, SolarWinds sells some, there's 0:01:19.020000 --> 0:01:20.840000 something called PRTG. 0:01:20.840000 --> 0:01:21.720000 You can just Google it. 0:01:21.720000 --> 0:01:26.660000 There's lots of SNMP NMS software available. 0:01:26.660000 --> 0:01:29.120000 Some of it's free, some of it costs some money. 0:01:29.120000 --> 0:01:31.320000 Now that stuff is running on a server. 0:01:31.320000 --> 0:01:34.620000 So normally when you think of a client -server architecture you'd say, 0:01:34.620000 --> 0:01:40.140000 oh, okay well if the NMS is running on an actual server like a Linux server 0:01:40.140000 --> 0:01:45.960000 that must be the server component of the client-server architecture. 0:01:45.960000 --> 0:01:48.380000 But in this case it's actually just reversed. 0:01:48.380000 --> 0:01:53.760000 You see in a client-server architecture normally we think of the client 0:01:53.760000 --> 0:01:57.720000 as sending a request to the server. 0:01:57.720000 --> 0:02:01.680000 The server is holding on to some sort of data, the client wants it and 0:02:01.680000 --> 0:02:03.580000 then the server responds back. 0:02:03.580000 --> 0:02:10.460000 Well in SNMP the SNMP manager is actually the one who's sending the request. 0:02:10.460000 --> 0:02:14.680000 So he is actually the client as far as SNMP is concerned. 0:02:14.680000 --> 0:02:19.440000 So the SNMP manager on which you're running SolarWinds or Cacti or whatever 0:02:19.440000 --> 0:02:23.440000 you're running as a software, that's where the request will be formatted 0:02:23.440000 --> 0:02:26.440000 and sent out. So he's the client. 0:02:26.440000 --> 0:02:28.380000 So who is actually the server? 0:02:28.380000 --> 0:02:30.860000 Well the server is the SNMP agent. 0:02:30.860000 --> 0:02:34.140000 He's the one who's holding on to the data that you want to get. 0:02:34.140000 --> 0:02:37.820000 Now the agent, that's most likely going to be your router or your switch. 0:02:37.820000 --> 0:02:44.160000 So an SNMP agent is actually a software sub-component or a piece of code 0:02:44.160000 --> 0:02:46.740000 that understands SNMP. 0:02:46.740000 --> 0:02:51.540000 That can take in an SNMP request, get the data that request is looking 0:02:51.540000 --> 0:02:55.560000 for and then send an SNMP response back out. 0:02:55.560000 --> 0:03:01.080000 So the SNMP agent can be almost anything that's capable of running SNMP 0:03:01.080000 --> 0:03:04.920000 software. Now in the context of this video we're thinking about networking 0:03:04.920000 --> 0:03:09.340000 devices. So for example your router or your switch, your firewall, they 0:03:09.340000 --> 0:03:11.520000 would all have SNMP agents in there. 0:03:11.520000 --> 0:03:14.360000 It's not like it's a piece of code that you have to specially load in 0:03:14.360000 --> 0:03:20.080000 there. For example Cisco iOS devices, Cisco iOS has SNMP agent functionality 0:03:20.080000 --> 0:03:24.200000 built into it. You just have to turn it on with a couple of commands. 0:03:24.200000 --> 0:03:26.480000 But other things could be SNMP agents as well. 0:03:26.480000 --> 0:03:30.840000 For example IP phones, even fax machines and printers could be queried 0:03:30.840000 --> 0:03:36.640000 via SNMP if they're running agent software within that device. 0:03:36.640000 --> 0:03:42.060000 Now when the SNMP agent gets a query for some information, it has to look 0:03:42.060000 --> 0:03:45.160000 somewhere to find the information and send it back. 0:03:45.160000 --> 0:03:50.600000 Where is the information stored within that agent? 0:03:50.600000 --> 0:03:55.580000 It's stored in another component called the management information base, 0:03:55.580000 --> 0:03:59.200000 the MIB. So just think of this as being a database or as it says here 0:03:59.200000 --> 0:04:03.620000 a data structure where variables are stored on the agent. 0:04:03.620000 --> 0:04:09.040000 So when the SNMP manager sends a request saying hey agent, give me the 0:04:09.040000 --> 0:04:12.980000 quantity of bytes that have passed through your interface fast ethernet 0:04:12.980000 --> 0:04:17.680000 00, that agent will look in the MIB and it will look for something called 0:04:17.680000 --> 0:04:22.420000 a MIB object that corresponds to that data that's being requested and 0:04:22.420000 --> 0:04:23.980000 then it'll send the data out. 0:04:23.980000 --> 0:04:27.700000 So here's sort of a graphical representation of what that looks like. 0:04:27.700000 --> 0:04:32.300000 So on the right is where we have our SNMP manager. 0:04:32.300000 --> 0:04:34.520000 So this is actually our physical server. 0:04:34.520000 --> 0:04:38.760000 For example our Linux server or our Ubuntu server or whatever happens 0:04:38.760000 --> 0:04:42.640000 to be. And that's running network management station. 0:04:42.640000 --> 0:04:45.040000 So he's an, he is an NMS. 0:04:45.040000 --> 0:04:47.360000 So that's the name of his role. 0:04:47.360000 --> 0:04:51.780000 He is a network management station and he's running some sort of SNMP 0:04:51.780000 --> 0:04:57.000000 software which gives him that ability to be an NMS. 0:04:57.000000 --> 0:05:01.300000 So it's his role to send out SNMP commands of which we'll look at some 0:05:01.300000 --> 0:05:03.080000 of those commands in just a moment. 0:05:03.080000 --> 0:05:07.540000 Now those commands are carried in IP and they're carried in UDP. 0:05:07.540000 --> 0:05:09.460000 So UDP and IP is what carries those. 0:05:09.460000 --> 0:05:11.040000 So it can go across the internet. 0:05:11.040000 --> 0:05:12.980000 It can go across an intranet. 0:05:12.980000 --> 0:05:15.280000 Any network that's capable of carrying them. 0:05:15.280000 --> 0:05:17.740000 And those commands are going to your agent. 0:05:17.740000 --> 0:05:20.000000 So your agent could be a router, a switch. 0:05:20.000000 --> 0:05:25.200000 It could be a firewall, a printer, an IP phone. 0:05:25.200000 --> 0:05:28.820000 So that agent has to be running some agent software which in the case 0:05:28.820000 --> 0:05:31.560000 of routers and switches is already preloaded. 0:05:31.560000 --> 0:05:34.820000 And it also has to have a special database called a MIB database, Management 0:05:34.820000 --> 0:05:37.100000 Information Base. 0:05:37.100000 --> 0:05:46.480000 So just once again an SNMP agent is a device running SNMP software that 0:05:46.480000 --> 0:05:50.500000 contains a MIB. For example here we see some routers and switches that 0:05:50.500000 --> 0:05:52.320000 could be that functionality. 0:05:52.320000 --> 0:05:57.340000 Now let's just talk about the MIB a little bit more here. 0:05:57.340000 --> 0:06:02.100000 So as I mentioned, MIB stands for Management Information Base. 0:06:02.100000 --> 0:06:03.520000 It's a database. 0:06:03.520000 --> 0:06:08.600000 It's a database of structured data called variables or objects which are 0:06:08.600000 --> 0:06:10.860000 stored in a hierarchical fashion. 0:06:10.860000 --> 0:06:12.460000 What the heck does that stand for? 0:06:12.460000 --> 0:06:15.200000 All right, let's keep going on here. 0:06:15.200000 --> 0:06:19.740000 So if you recall from a previous video I gave or videos from other instructors 0:06:19.740000 --> 0:06:24.980000 or just something you've read, you remember that way back in 1988, there 0:06:24.980000 --> 0:06:28.900000 was an RFC that came out, I think it was RFC 1065 or somewhere around 0:06:28.900000 --> 0:06:30.820000 there. They said, you know what? 0:06:30.820000 --> 0:06:36.700000 We should sort of conceptualize and standardize what devices have inside 0:06:36.700000 --> 0:06:39.620000 them. For example, devices have interfaces. 0:06:39.620000 --> 0:06:42.480000 Okay, we should have a number for interface. 0:06:42.480000 --> 0:06:44.840000 In what do interfaces store? 0:06:44.840000 --> 0:06:47.760000 Well, regardless of what device you are, an interface typically stores 0:06:47.760000 --> 0:06:52.320000 counters. All right, let's put a number for interface encounters. 0:06:52.320000 --> 0:06:54.140000 Okay, what do counters typically store? 0:06:54.140000 --> 0:06:56.520000 Well, they typically store like bit counts. 0:06:56.520000 --> 0:06:59.740000 Okay, let's do a number for interface counter bit counts. 0:06:59.740000 --> 0:07:01.260000 They store byte counts. 0:07:01.260000 --> 0:07:03.280000 They store counters of errors. 0:07:03.280000 --> 0:07:06.440000 So they said, let's standardize all this stuff. 0:07:06.440000 --> 0:07:12.240000 And then each one of these things is accessible in a MIB via this tree. 0:07:12.240000 --> 0:07:16.460000 Now, as you go along the tree, every element in the tree is referenced 0:07:16.460000 --> 0:07:20.960000 by a number. This is what we call the MIB hierarchy or the MIB tree. 0:07:20.960000 --> 0:07:23.600000 Let me show you an example of this. 0:07:23.600000 --> 0:07:26.040000 So here's like the MIB structure. 0:07:26.040000 --> 0:07:32.180000 So when an SNMP query goes out, when the network management system, the 0:07:32.180000 --> 0:07:37.600000 NMS send out an SM inquiry, it does not say in plain text, if you caught 0:07:37.600000 --> 0:07:40.840000 it in a stiffer trace or something, you wouldn't see in plain text that 0:07:40.840000 --> 0:07:45.680000 query saying, hey, router five, I want to talk to you. 0:07:45.680000 --> 0:07:49.500000 I want information about all of your interfaces, specifically fast, even 0:07:49.500000 --> 0:07:54.680000 at zero, zero, and the quantity of bytes have gone in the outbound direction. 0:07:54.680000 --> 0:07:59.340000 Now that would be nice if it did it in clean clear text or plain text. 0:07:59.340000 --> 0:08:02.660000 So we could see that in the sniffer trace, but that's not the way it works. 0:08:02.660000 --> 0:08:07.760000 Every one of those things as asking for is identified as a MIB object, 0:08:07.760000 --> 0:08:09.780000 which gives a number to it. 0:08:09.780000 --> 0:08:12.740000 So for example, you can see right here. 0:08:12.740000 --> 0:08:21.120000 If my NMS was sending out a message, an SNMP message, and ultimately that 0:08:21.120000 --> 0:08:25.480000 message had something to do with a Cisco device, and it was trying to 0:08:25.480000 --> 0:08:29.200000 get some information about interfaces, it would have to go through this 0:08:29.200000 --> 0:08:34.260000 tree. So if we actually caught that message in a wire shark sniffer capture, 0:08:34.260000 --> 0:08:37.040000 we'd see something like this, he'd be saying, okay, here's what I'm asking 0:08:37.040000 --> 0:08:45.600000 for. Dot one, dot three, dot six, dot one, dot four, dot one, dot nine, 0:08:45.600000 --> 0:08:47.880000 dot two, dot two. 0:08:47.880000 --> 0:08:52.580000 I think that covers all the objects in this tree if I didn't miss anything. 0:08:52.580000 --> 0:08:56.580000 So if it sent out a request, and by the way, request is not technically 0:08:56.580000 --> 0:09:01.040000 the name of an SNMP message, but I'm just using it as an example here, 0:09:01.040000 --> 0:09:08.220000 if you sent out a request for this, that is called an object identifier. 0:09:08.220000 --> 0:09:11.040000 That is stored in our MIB. 0:09:11.040000 --> 0:09:16.740000 So the SNMP agent, the router, the switch, the firewall, this running 0:09:16.740000 --> 0:09:21.920000 agent software, when he gets a request for this object identifier, he 0:09:21.920000 --> 0:09:29.260000 will go into his MIB, which is just a database storing tons of information. 0:09:29.260000 --> 0:09:34.700000 And he might say, okay, well, in my MIB, right here is the location where 0:09:34.700000 --> 0:09:37.400000 I'm storing this information. 0:09:37.400000 --> 0:09:40.580000 I'll extract whatever information I have from right there. 0:09:40.580000 --> 0:09:45.120000 If it says interface group, well, we haven't gone very deep at this point. 0:09:45.120000 --> 0:09:47.840000 So it might be, okay, let me tell you what interfaces I have. 0:09:47.840000 --> 0:09:51.160000 Fast Ethan at zero, zero, zero, one, one, zero, one, two, and then it 0:09:51.160000 --> 0:09:53.900000 probably keeps going deeper than that. 0:09:53.900000 --> 0:09:57.840000 So each one of those things, each one of those things you could get via 0:09:57.840000 --> 0:10:02.440000 SNMP is stored in this database called a MIB and it's accessible via an 0:10:02.440000 --> 0:10:05.840000 object identifier, an OID. 0:10:05.840000 --> 0:10:10.320000 Now, here's the good news. 0:10:10.320000 --> 0:10:16.020000 99% of the time when you are working with SNMP, the NMS that you're working 0:10:16.020000 --> 0:10:22.740000 on is a GUI based NMS with pull down windows and radio buttons and things 0:10:22.740000 --> 0:10:23.980000 that you can select. 0:10:23.980000 --> 0:10:28.080000 So you won't even have to know what the OIDs are. 0:10:28.080000 --> 0:10:32.060000 You can just select from a pull down menu or something, interface statistics 0:10:32.060000 --> 0:10:36.960000 or system uptime or routing table. 0:10:36.960000 --> 0:10:41.080000 And the NMS will know in the background what that big long string of numbers 0:10:41.080000 --> 0:10:45.120000 is, what the correct OIDs for that thing that you just selected. 0:10:45.120000 --> 0:10:50.400000 Now, if you're using a text based or a CLI based NMS where you have to 0:10:50.400000 --> 0:10:56.420000 actually type in an S&P command, then yes, that gets very, very painful 0:10:56.420000 --> 0:10:59.580000 because as part of your command, you have to type in this big long string 0:10:59.580000 --> 0:11:03.940000 of numbers corresponding to the OID of what it is that you're trying to 0:11:03.940000 --> 0:11:08.400000 get. That's why most people, 99% of the people would use a graphical based 0:11:08.400000 --> 0:11:16.680000 S&P system so they don't have to be coded it with the MIBS and it has 0:11:16.680000 --> 0:11:19.980000 in the background of the software what all the various numbers are and 0:11:19.980000 --> 0:11:21.440000 what they correspond to. 0:11:21.440000 --> 0:11:25.560000 So this is just for your reference so you know how in the background how 0:11:25.560000 --> 0:11:30.540000 SNMP is working between the NMS and the agent is querying things for these 0:11:30.540000 --> 0:11:34.420000 object identifiers referenced by these strings of numbers. 0:11:34.420000 --> 0:11:38.780000 And all these OIDs, which are thousands of them, are stored in this big 0:11:38.780000 --> 0:11:43.060000 database called the Management Information Base. 0:11:43.060000 --> 0:11:48.600000 All right. So talking a little bit more here about the network management 0:11:48.600000 --> 0:11:54.960000 station, we already know this is a server running NMS software and it 0:11:54.960000 --> 0:11:56.620000 can be done in one of two ways. 0:11:56.620000 --> 0:12:01.280000 Usually what happens is that in the NMS, which is a graphical system like 0:12:01.280000 --> 0:12:04.900000 we see right here, you will set it up in advance and you'll say, okay, 0:12:04.900000 --> 0:12:10.020000 here's the device I want you to talk to. 0:12:10.020000 --> 0:12:12.600000 Of those devices you want to reach out to. 0:12:12.600000 --> 0:12:19.420000 Now your typical routers and switches and firewalls by default are not 0:12:19.420000 --> 0:12:21.880000 enabled for SNMP. 0:12:21.880000 --> 0:12:25.060000 So if you go to the NMS and you give it the IP addresses of your routers 0:12:25.060000 --> 0:12:28.160000 and switches and firewalls and it starts querying them, it's not going 0:12:28.160000 --> 0:12:32.260000 to get any response back because those devices are not listening on UDP 0:12:32.260000 --> 0:12:37.220000 port 161. So at a very minimum, we have to go to our routers and switches 0:12:37.220000 --> 0:12:41.480000 and firewalls and configure at least a couple of commands minimum to get 0:12:41.480000 --> 0:12:44.100000 them working so they're in a listening state. 0:12:44.100000 --> 0:12:49.280000 So they actually recognize that they are supposed to be SNMP agents. 0:12:49.280000 --> 0:12:51.140000 Okay. So now we've done that. 0:12:51.140000 --> 0:12:54.380000 We have configured the routers switch firewall in advance so it knows 0:12:54.380000 --> 0:12:56.420000 it's supposed to be an SNMP agent. 0:12:56.420000 --> 0:13:00.360000 We've configured the NMS and we've told them, here's the IP address of 0:13:00.360000 --> 0:13:03.300000 router one. Here's the IP address of switch two. 0:13:03.300000 --> 0:13:04.480000 So he knows that. 0:13:04.480000 --> 0:13:07.920000 Now the only thing left to do is you have to decide, do you want this 0:13:07.920000 --> 0:13:12.580000 thing set up to where it pulls it on a fairly frequent basis? 0:13:12.580000 --> 0:13:13.940000 And that's usually what people do. 0:13:13.940000 --> 0:13:17.620000 They'll have the NMS set up so that every five minutes or so, or every 0:13:17.620000 --> 0:13:21.940000 one minute, whatever you want, it will pull the various devices and collect 0:13:21.940000 --> 0:13:23.340000 these statistics. 0:13:23.340000 --> 0:13:27.020000 And that way it can start creating graphs and bot pie charts. 0:13:27.020000 --> 0:13:30.720000 And you can see, okay, here's how the CPU has looked over time. 0:13:30.720000 --> 0:13:32.480000 You can click on another pie chart. 0:13:32.480000 --> 0:13:36.560000 All right. Here's how my interfaces have looked over time as far as utilization. 0:13:36.560000 --> 0:13:40.880000 So polling is the most preferential and most common way that people set 0:13:40.880000 --> 0:13:45.380000 up their NMS. But you can also have the NMS send out messages manually. 0:13:45.380000 --> 0:13:48.540000 You could click a button and say, hey, send out a request right now to 0:13:48.540000 --> 0:13:51.980000 router two. I want to get some on the spot information right here. 0:13:51.980000 --> 0:13:57.200000 So it can be done in an unsolicited form or it can be triggered. 0:13:57.200000 --> 0:14:01.760000 The last thing I want to mention here on this slide also is that most 0:14:01.760000 --> 0:14:05.960000 of the time, the way SNMP works is that the network management station 0:14:05.960000 --> 0:14:10.000000 is polling the agent on a regular frequent interval. 0:14:10.000000 --> 0:14:14.520000 But the agent itself, the router, the switch could also be configured 0:14:14.520000 --> 0:14:17.560000 to send what's called an SNMP trap. 0:14:17.560000 --> 0:14:21.560000 Now, what happens with that is if the router or switch, if you've configured 0:14:21.560000 --> 0:14:27.180000 to do this, if a certain trigger happens like an interface goes down or 0:14:27.180000 --> 0:14:31.700000 a routing neighbor comes up or disappears, you might say to yourself, 0:14:31.700000 --> 0:14:35.720000 you know what, if something like that happens, that's pretty critical. 0:14:35.720000 --> 0:14:39.640000 And if my polling is happening every five or 10 minutes, I don't want 0:14:39.640000 --> 0:14:43.540000 to wait for the next polling interval to find out about that. 0:14:43.540000 --> 0:14:47.460000 So you can configure your router or switch your SNMP agent to send what's 0:14:47.460000 --> 0:14:52.760000 called a trap, which means if this event happens, if this trigger happens, 0:14:52.760000 --> 0:14:57.520000 I want you to unsolicited send out a trap message to the NMS. 0:14:57.520000 --> 0:15:01.100000 I want you to let the NMS know, hey, this just happened. 0:15:01.100000 --> 0:15:04.220000 So it's probably going to happen in between polling intervals. 0:15:04.220000 --> 0:15:07.560000 But that's good, because we want the NMS to know about that as soon as 0:15:07.560000 --> 0:15:11.460000 it happens. All right, so let's just finish up here really quickly with 0:15:11.460000 --> 0:15:15.240000 some of the more common SNMP message types. 0:15:15.240000 --> 0:15:20.120000 So I've been using the term an SNMP request, but that's not technically 0:15:20.120000 --> 0:15:21.180000 what they're called. 0:15:21.180000 --> 0:15:24.840000 So if you're trying to get or request some information from a device from 0:15:24.840000 --> 0:15:31.880000 an agent, technically what you're sending is what's called an SNMP polling 0:15:31.880000 --> 0:15:34.360000 mechanism from the NMS. 0:15:34.360000 --> 0:15:38.200000 And you're polling a particular object ID from the MIB. 0:15:38.200000 --> 0:15:43.560000 Remember an object ID is that 1.3.6 .4.7, which corresponds to some piece 0:15:43.560000 --> 0:15:48.300000 of information you're trying to get from the agent. 0:15:48.300000 --> 0:15:53.440000 So this is typically automated to occur at predefined intervals. 0:15:53.440000 --> 0:15:59.540000 Now of less common usage is something called an SNMP set message. 0:15:59.540000 --> 0:16:05.780000 An SNMP set message can actually be used to program or configure the device. 0:16:05.780000 --> 0:16:10.580000 So believe it or not, I could go into a router switch, give it basic IP 0:16:10.580000 --> 0:16:15.940000 connectivity, give it basic routing functionality, turn on a couple of 0:16:15.940000 --> 0:16:17.720000 SNMP commands and walk away. 0:16:17.720000 --> 0:16:18.920000 Now I haven't done anything else. 0:16:18.920000 --> 0:16:20.440000 I haven't done any security. 0:16:20.440000 --> 0:16:21.700000 I haven't done any NAT. 0:16:21.700000 --> 0:16:25.560000 I haven't done anything but basic IP, basic SNMP. 0:16:25.560000 --> 0:16:33.240000 And now from my server, that device remotely. 0:16:33.240000 --> 0:16:39.940000 Now like I said, most people don't use SNMP to modify or change the configuration 0:16:39.940000 --> 0:16:42.880000 of a device. But you can. 0:16:42.880000 --> 0:16:46.160000 That's what an SNMP set message is for. 0:16:46.160000 --> 0:16:49.260000 And there's an SNMP response. 0:16:49.260000 --> 0:16:53.660000 So when you send, when the NMS sends out an SNMP get message, hey, I'd 0:16:53.660000 --> 0:16:55.320000 like to get this OID. 0:16:55.320000 --> 0:16:56.900000 Please give me some information. 0:16:56.900000 --> 0:17:00.760000 It will be an SNMP response that comes back, contain the information that 0:17:00.760000 --> 0:17:03.540000 you're looking for. 0:17:03.540000 --> 0:17:07.920000 I also mentioned something about SNMP traps, which is an unsolicited message 0:17:07.920000 --> 0:17:12.000000 that's sent out by the agent when a certain trigger or event happens. 0:17:12.000000 --> 0:17:13.660000 Now this doesn't happen automatically. 0:17:13.660000 --> 0:17:15.800000 You have to configure it to do this. 0:17:15.800000 --> 0:17:19.760000 Now with an SNMP trap, there is no acknowledgement. 0:17:19.760000 --> 0:17:21.920000 Remember, this is all UDP right here. 0:17:21.920000 --> 0:17:33.160000 So in SNMP to the NMS or not, it had no idea if the NMS actually got it. 0:17:33.160000 --> 0:17:35.160000 It was just unacknowledged. 0:17:35.160000 --> 0:17:38.960000 Well, with the invention of SNMP version three, they said, you know what, 0:17:38.960000 --> 0:17:44.340000 we should have something similar to a trap that the agent sends when something's 0:17:44.340000 --> 0:17:48.740000 triggered, but that gets acknowledged by the NMS. 0:17:48.740000 --> 0:17:53.200000 And that's what's called an SNMP inform only available in version three. 0:17:53.200000 --> 0:17:57.160000 But now you actually get an acknowledgement back from an NMS that he received 0:17:57.160000 --> 0:18:00.880000 it. So that concludes this video. 0:18:00.880000 --> 0:18:01.580000 Thank you for watching.