ELSA Cable manual Deleting rows in tables using Snmp, Appending rows to tables using Snmp

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26Configuration modes

Bear in mind that the access protection given by the community mechanism in the SNMP V.1 is only very limited since the data, the MIB IDs and the communities are not encrypted in the UDP data blocks of requests and responses as they are transmitted.

Deleting rows in tables using SNMP

SNMP itself has no mechanisms intended for deleting. You therefore have to use a trick to delete entries from tables.

If you need to delete a row, you have to change the index entry value, i.e. the value in the first column, to its current value.

KExample: You want to delete the 3rd row from following IP routing table.

IP address	IP-netmask	Router name	Distance
192.168.0.0	255.255.0.0	0.0.0.0	0
172.16.0.0	255.240.0.0	0.0.0.0	0
10.0.0.0	255.0.0.0	ROBERT	0
224.0.0.0	224.0.0.0	0.0.0.0	0

The entry '10.0.0.0' (i.e. the first cell of the third row) is amended in the manager to its current value, i.e. to '10.0.0.0', and the Set command is sent off. The SNMP SetRequest now contains the command to amend the first cell of the third row to '10.0.0.0'. The SNMP software recognizes that this assignment to the index is redundant and interprets it as a delete command.

Appending rows to tables using SNMP

There are two ways of inserting rows in a table:

KUsing the set command will result in a new row through setting a new index entry. By using the command in the syntax:

someTable.1.2.2 = xyz

a row with index '2' will be generated in the table 'someTable', with the entry 'xyz' in its second column. The '1' after the table name is constant for this command and stands for 'someEntry' in the SNMP-Syntax.

KWhen using SNMP managers that do not allow the entry of index values, it is possible to amend any existing index entry to the new index value of the new row. The row which has been used as the source for the amendment will itself remain unchanged.

If we take Castlerock SNMPc as an example, the first possibility can be realized as follows:

aActivate the Display MIB Table item in the Manage menu of Castlerock SNMPc.

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