I am writing a function block in RTU so it gets an OID and gives the value. I have realised in Wireshark that every OID has its own request-id which is specific. I want to know if there is a special way to figure out the request-id without having to go through Wireshark.
Related
I'm working on a Go program that receives packets and wants to see receipt timestamps.
In C this would be done by setting the SO_TIMESTAMP/SO_TIMETAMPNS socket option and then using the CMSG macros to extract data from a control message buffer structure,
I have searched the Go documentation for a way to do this, in vain. Can anyone point me art a working example?
You can get them from UDPConn::ReadMsgUDP, the ancillary data was named "oob" for some weird reason, but it is the ancillary channel with the control messages.
You can parse the []byte with the control message data using x/sys/unix::Cmsghdr (https://pkg.go.dev/golang.org/x/sys/unix#Cmsghdr)
There should be a better way, but at least this is not behind "internal"...
I am trying to make a snmp trap receiver, that can capture all the incoming snmp trap from UDP 162 port and translate them into meaningful alarms. The image I attached is a sample trap that I captured using wireshark.
My script can capture and parse all different parts of the packet, but I got stuck in the variable binding section. Im not sure how I can re-present this section into some user friendly information (that I can show in the user interface). How do I know these sequences are sending something alarming or just some general information regarding the agent node? are these sequences independent information each or together they are forming one piece of information?
As with any incoming data, it is important to know what kind of info you are getting. The variable bindings of an SNMP trap is basically a hierarchical piece of data. Every object or element represents it's own data. If you take the first element (1.3.6.1.2.1.1.3.0) you will find that this contains the sysUpTime (see link), which is pretty general.
Most of the other elements seem to start with 1.3.6.1.4.1.4421 which appears to be object from a specific vendor; Santera systems (see link). You might want to try and contact them in order to obtain their MIB (Management Information Base), which should have details on what kind of data is shown in these fields.
It might be possible to find info like this online, have a look at the XML-files on this link.
Most of the examples provided for sending SNMP traps are simple ones like the one below.
snmptrap -v 1 -c public host TRAP-TEST-MIB::demotraps localhost 6 17 '' \
SNMPv2-MIB::sysLocation.0 s "Just here"
Take any MIB file, they contain many complex object groups, for example, systemGroup contains sysLocation, sysName, etc.
Could someone help in bringing out examples to show the way how to send snmp traps which includes such OBJECT-GROUPS. Adding one more question here, Does SNMPTRAPD support internationalization?
It is really bad practice to define the SNMP notification (trap or inform) the way that it contains the entire OBJECT GROUP or even worse the entire SNMP table. The reason is that you don't really need all these variables anyway. The other reason is that the packet/PDU is limited by MTU size. So it is possible that you'll not be able to send the data within single UDP packet due to its size.
The proper scenario would be to have few varbinds and you could also initiate some polling cycle to find out what happens if you need more details when you receive such trap.
SNMPTRAPD and NET-SNMP library in general do not support internationalization (UNICODE). The library is limited to ASCII charset only.
There are commercial products on the market including NetDecision TrapVision and some other that fully support UTF-8 internationalization.
Can anyone tell me why NMS implementations parse and save MIB items in a database?
I know one of the reasons is when they receive a trap and want to analyze it, then they use the parsed MIB. What else they do with parsed MIB?
For example, when the NMS sends a SNMP GET request to an agent, the programmer must specify which OIDs are being requested?
Does the the parsed MIB have a another purpose or do we parse MIBs only for analyzing SNMP traps?
You are on the right track - you parse the MIB at all in order to make it human-readable. That is for both traps (informs) and polled values. But if you parse it out to a text file, that's a huge amount of data to read/grep through to find out the description, message, possible values, related OIDs, etc.
Added to this is that there isn't just one MIB. There are dozens or hundreds that an NMS may be interested in. Since, on a host, you only add the MIBs that you want that host to respond to, the NMS has to have a copy of every MIB that ever device it is monitoring may have on IT so that it can understand the response the host returns.
So you parse each MIB and store it in a db to make it faster to search and to have everything all in one place. That could be so that you can find the messages associated with varbinds, or what all the possible enumerations are, etc.
Just to be clear, parsing the MIB isn't the same as doing an SNMPWalk on a host. SNMPWalk just gives you the current response to each OID in sequence.
When I inject any packet via WinPcap it will be captured in this moment.
I dont want to capture packets, witch were injected myself.
What is the easiest way?
The best way is to use PCAP_OPENFLAG_NOCAPTURE_RPCAP flag..
You could perhaps use a capture filter (pcap_setfilter()) and filter out packets by their source MAC address.
That may not be exactly what you want though, because MAC addresses can be spoofed, you might want to see outgoing packets from other sources on your machine, etc.
The only other thing I can think of would be to compute a hash value of each packet you send, and discard any captured packet with the same hash value.
There's got to be a better way…