No Reponse over SNMP via TCP

[Colosus]

I am stumped on this one and could use some advice. I have approximately 50 linux servers that I'm monitoring with cacti via SNMP. I use SSH tunnels to connect to each agent and the query over SNMP via TCP.

Two of these servers return a "No Response" message when queried, even locally. SNMP is listening on TCP:161, the community is fine as it works if I change it to UDP. I can see the query attempts in /var/log/messages, but it just returns nothing.

Just so you know I'm not crazy...

14 copenhagen:/> snmpwalk -c public -v 1 localhost
SNMPv2-MIB::sysDescr.0 = STRING: Linux copenhagen 2.6.18-8.el5 #1 SMP Thu Mar 15 19:57:35 EDT 2007 i686
...

17 copenhagen:/> snmpwalk -c public -v 1 tcp:localhost
Timeout: No Response from tcp:localhost


19 copenhagen:/> netstat -a
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 *:snmp *:* LISTEN
...
udp 0 0 *:snmp *:*
...

[root@copenhagen /]# tail /var/log/messages
Nov 9 15:36:32 copenhagen snmpd[8128]: Connection from TCP: [127.0.0.1]:-5469
Nov 9 15:36:32 copenhagen snmpd[8128]: Received SNMP packet(s) from TCP: [127.0.0.1]:-5469
Nov 9 15:36:33 copenhagen snmpd[8128]: Connection from TCP: [127.0.0.1]:-5469


Does anyone have any idea what can cause this? Like I said, so far I've only got 2 out of 50 that have this problem, but I'd like to get it fixed. Thanks in advance.

[gandalf]

Please visit fmangeant's snmp howto (see first link of my signature) to verify SNMP/TCP setup. I'm not used to this stuff, so I hope that it will help
Reinhard