Red Hat Bugzilla – Bug 886468
snmpd does not report error when clientaddr <ip>:<port> cannot bind to the specified port
Last modified: 2015-07-22 03:22:05 EDT
+++ This bug was initially created as a clone of Bug #840861 +++ Description of problem: Having following /etc/snmp/snmpd.conf file, if snmpd fails to bind the specified clientaddr port, it quietly uses random port instead. It should at least report some error to system log. rocommunity public [snmp] clientaddr 127.0.0.1:30000 trapsink localhost public Version-Release number of selected component (if applicable): net-snmp-5.5-41.el6 How reproducible: always Steps to Reproduce: 1. vi /etc/snmp/snmpd.conf 2. nc -ul localhost 30000 (or have SELinux in enforcing mode) 3. service snmpd start Actual results: - traps are sent from random port and not from port 30000, which is taken by 'nc' - system log is empty Expected results: - system log should show an error
The trap is actually sent on IPv6 if the port 30000 is already used on IPv4. It seems like there is some kind of fallback to IPv6 implemented. 17:10:29.409052 IP6 (hlim 64, next-header UDP (17) payload length: 52) ::1.46569 > ::1.162: [udp sum ok] { SNMPv1 { Trap(29) .1.3.6.1.4.1.8072.3.2.10 192.168.122.206 coldStart 5 } }
You should have '[snmp] clientaddrUsesPort yes' in your snmpd.conf. With that, no trap is sent and I get in /var/log/messages: Dec 13 11:17:17 rhel6 snmpd[29457]: getaddrinfo("localhost", NULL, ...): No address associated with hostname Dec 13 11:17:17 rhel6 snmpd[29457]: snmpd: create_trap_session: Dec 13 11:17:17 rhel6 snmpd[29457]: /etc/snmp/snmpd.conf: line 2: Error: cannot create trap2sink: localhost Dec 13 11:17:17 rhel6 snmpd[29457]: net-snmp: 1 error(s) in config file(s) I admit the first message is quite confusing. RHEL 6.4 misses patch fixed in 5.9 as #840861.
This request was not resolved in time for the current release. Red Hat invites you to ask your support representative to propose this request, if still desired, for consideration in the next release of Red Hat Enterprise Linux.
snmpd will now log "Cannot bind for clientaddr 127.0.0.1:30000: Address already in use"
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://rhn.redhat.com/errata/RHSA-2015-1385.html