Sending informs from a specific ip address

Version: net-snmp 5.4.2

We have the requirement that we need to send informs from a specific 
ipv4 address, as we use the source address to do a lot of the routing on 
our device.  The device can have multiple ipv4 addresses, and in that 
situation there is typically a separate address intended for management 
traffic.  We can get snmpd to bind to that address on port 161 for the 
usual GET, SET, etc. processing via the agentaddress token.  Where we 
are having trouble is getting v3 informs sent off that same interface. 
In our setup we use trapsess to configure the targets, and all informs 
are going through snmpd (either snmpd is sending its own informs, or 
informs are originating from AgentX subagents).

My apologies in advance if any of the example output or config files 
wrap badly.

A sample configuration file (mildly obfuscated) looks like:

rwuser userblah
agentaddress localhost:161,192.168.222.5:161
clientaddr 192.168.222.5

trapsess -v 3 -u userblah -l authNoPriv -A somepassword -a MD5 -Ci 
10.11.10.92

trapsess -v 3 -u userblah -l authNoPriv -A somepassword -a MD5 -Ci 
192.168.223.10

 From 'tcpdump -i any port 162' I get:

<snip/>
-3:-52:-11.248169 IP 10.116.0.210.32785 > 10.11.10.92.snmptrap:  F=r [|snmp]
-3:-52:-10.248665 IP 10.116.0.210.32786 > 192.168.223.10.snmptrap:  F=r 
[|snmp]
<snip/>

Obviously at this point I was expecting to see 192.168.222.5 as the 
source address, not 10.116.0.210 which is the first ipv4 address 
configured for the box.

And to be complete 'lsof -p <pid> -P' gives me:

<snip/>
snmpd   6732 root    7u  IPv4     482968            UDP *:32785
snmpd   6732 root    8u  IPv4     482969            UDP *:32786
snmpd   6732 root    9u  IPv4     482972            UDP 
localhost.localdomain:161
snmpd   6732 root   10u  IPv4     482973            UDP 192.168.222.5:161
<snip/>

Again, I was expecting the sockets to be bound to 192.168.222.5 rather 
than INADDR_ANY.

Grubbing through the various mailing list archives and patches, I 
thought this had been resolved in 5.4.2 with patch 1775124. 
Specifically, I thought that the clientaddr configuration token would 
correctly set the source address of the outgoing UDP packet to the 
configured address.  Instead, we see that its still binding to 
INADDR_ANY and the inform is coming from the first available ip address. 
  To be thorough, I thought that perhaps it mattered which configuration 
file the clientaddr directive was used; it doesn't.  I tried it in both 
snmp.conf and snmpd.conf and there was no discernible result.

Am I barking up the wrong tree with clientaddr?  Is there something 
we've missed in our use of the trapsess token?  I checked all the 
options available to trapsess in 'man snmpcmd' and there is nothing to 
specify the source address.

Thanks,
-- 
Glenn McAllister     <[email protected]>      +1 416 348 1594
SOMA Networks, Inc.  http://www.somanetworks.com/  +1 416 977 1414

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