Monitoring Tools 14-15By default, the read-only and read/write community strings are set to public and private, respectively. Youshould change both of the default community strings to values known only to you and trusted system adminis-trators.To change a community string, select it and enter a new value.Starting with the version 4.3 firmware, setting the Read-Only and Read-Write community strings to the emptystring will block all SNMP requests to the router. (The router may still send SNMP Traps if those are properlyenabled.)Previously, if either community string was the empty string, SNMP Requests specifying an empty communitystring were accepted and processed.This change is designed to allow the administrator to block SNMP access to the router and to provide moregranular control over the allowed SNMP operations to the router. Setting only the Read-Write community string to the empty string will block SNMP Set Requests to therouter, but Get Requests and Get-Next Requests will still be honored using the Read-Only community string(assuming that is not the empty string). Setting only the Read-Only community string to the empty string will not block Get Requests or Get-NextRequests since those operations (and Set Requests) are still allowed using the (non-empty) Read-Writecommunity string.Even if you decide not to use SNMP, you should change the community strings. This prevents unauthorizedaccess to the Netopia 4752 through SNMP. For more information on security issues, see “Suggested SecurityMeasures” on page 13-1.SNMP trapsAn SNMP trap is an informational message sent from an SNMP agent (in this case, the Netopia 4752) to amanager. When a manager receives a trap, it may log the trap as well as generate an alert message of its own.Standard traps generated by the Netopia 4752 include the following: An authentication failure trap is generated when the router detects an incorrect community string in areceived SNMP packet. Authentication Traps Enable must be On for this trap to be generated. A cold start trap is generated after the router is reset. An interface down trap (ifDown) is generated when one of the router’s interfaces, such as a port, stopsfunctioning or is disabled. An interface up trap (ifUp) is generated when one of the router’s interfaces, such as a port, beginsfunctioning.The Netopia 4752 sends traps using UDP (for IP networks).You can specify which SNMP managers are sent the IP traps generated by the Netopia 4752. Up to eightreceivers can be set. You can also review and remove IP traps.To go to the IP Trap Receivers screen, select IP Trap Receivers. The IP Trap Receivers screen appears.
