snmptrapd does not resolve hostnames / debug token

I load snmptrapd as follows:

/usr/local/sbin/snmptrapd -Lsd -p /var/run/snmptrapd.pid

And it resolves hostnames in the traps it logs in the following fashion
('tuk-cold-emu' is the hostname):

Mar  1 00:24:29 loghost snmptrapd[28435]: 2012-03-01 00:24:29
tuk-cold-emu [10.18.208.15] (via UDP:
[10.18.208.15]:45911->[10.18.42.13]:162) TRAP, SNMP v1, community secret
PowerNet-MIB::apc Enterprise Specific Trap
(PowerNet-MIB::apcEnvLowTempThresholdViolation) Uptime: 13 days,
14:09:51.95        ...

yum installs patches regularly ... but I haven't rebooted in a year or
more ... I rebooted a few days ago ... and snmptrapd no longer resolves
hostnames:

Mar 30 00:20:51 loghost snmptrapd[21184]: 2012-03-30 00:20:51
10.18.208.15(via UDP: [10.18.208.15]:40058->[10.18.42.13]:162) TRAP,
SNMP v1, community secret      PowerNet-MIB::apc Enterprise Specific
Trap (PowerNet-MIB::apcEnvLowTempThresholdViolation) Uptime: 42 days,
13:05:59.55  [....]

i.e. snmptrapd is behaving as though I had loaded it with the '-n'
flag.  But I haven't:

loghost> ps -ef | grep snmptrapd
root     15603     1  0 14:59 ?        00:00:16
/usr/local/sbin/snmptrapd -Lsd -p /var/run/snmptrapd.pid
loghost>

The usual utilities resolve names fine:
loghost> host 10.18.208.15
15.208.18.10.in-addr.arpa domain name pointer TUK-COLD-EMU.COMPANY.COM
loghost>

net-snmp-5.7.1
CentOS 5.8

I'm looking for a debug token which might help shed light on this:
http://www.net-snmp.org/wiki/index.php/Debug_tokens_5.4.2.1

But I don't see anything obvious (when searching for 'name' or 'host' or
'addr').

Any suggestions on a debug token to try?  Other suggestions for
trouble-shooting?

--sk

Stuart Kendrick
FHCRC

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