InterMapper requires that SNMP be available and configured to display traffic information. The most common cause of not being able to see traffic is that you haven't entered the SNMP Read-only community string. (This is like a password that controls whether another computer can retrieve SNMP information.)
In order of simplest to most complex, here is a list of reasons that InterMapper might not get SNMP information from a device:
Wrong DNS name/IP address - (not likely, but we have to mention it)
No connectivity - Can you ping the device from InterMapper?
No SNMP agent on the device - Many devices or computers have optional SNMP capabilities that must be installed separately.
Is the SNMP agent disabled? - Many devices allow you to disable the SNMP capability totally, or from certain ports.
If the SNMP agent is based on net-snmp or UCD-snmp package - be sure that the configuration file specifically lists InterMapper's IP address/subnet as an allowed client
In a custom probe, have you specified the OID properly? - (See the OID Format FAQ for details.)
Wrong Community string - A couple suggestions: Be sure to try 'public' (without the quotes); check your typing - community strings are case-sensitive.
Access lists: does the equipment only allow SNMP access from certain addresses?
Firewalls can interfere with InterMapper's traffic.
Does a firewall block the SNMP port between the InterMapper server and the equipment?
Certain firewalls may also block SNMP packets if it suspects that those packets are part of an attack. InterMapper may send and receive all its SNMP queries on the same port and after awhile the firewall may detect this.
Bugs in the SNMP agent on the equipment - InterMapper uses SNMP Get-Next-Requests in several places. We've seen certain equipment that fails when queried this way.
