I'm using the trial period version of NPM. Network discovery finds a dLink print server using port 161 and SNMP v1. However, it only discovers workstations on the network with ICMP. After installing and configuring SNMP on two Windows XP SP3 workstations according to Microsoft instructions, NPM still can't validate them. I've set them up with community string 'public' for READ ONLY privileges and have set them to accept SNMP packets from any host. I've opened TCP port 161 on the the two workstations in Windows Firewall. What am I missing?
Are there any firewalls in between somewhere? If so this could be were ping is permitted but not snmp. Also look in the event logs for clues or on one of xp machines run wireshark and look and see if the traffic from NPM is coming in on port 161 from your NPM machine.