RE: Sending informs from a specific ip address

> From: Glenn McAllister [mailto:[email protected]] 
> Sent: Thursday, October 16, 2008 9:45 AM


> 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. 

	Then you have misconfigured your IP routing.

> 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).

	This is typical.

> 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

	I vaguely recall trying to use agentaddress and not having it work as expected.  I see no documentation indicating that comma separated lists are acceptable.  Try using the snmpd command line listening address specification.

> clientaddr 192.168.222.5

	The clientaddr directive belongs in snmpconf, not snmpd.conf - no mix-n-match.

> 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, I'd guess, the default gateway?

> 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.

	See above re agentaddr.

> 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. 

	See above re clientaddr.

>   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.

	Correct - snmp.conf does not apply to snmpd.conf.

> 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.

	Setting a source address should not be necessary.  Add a routes for your 192.168.222/24 network and keep you target addresses in it, and the notifications will always come from that adapter, because that's how it's supposed to route.  You cannot have per-application routing tables, at least not on any OS I have yet encountered.


	HTH,

Mike

-------------------------------------------------------------------------
This SF.Net email is sponsored by the Moblin Your Move Developer's challenge
Build the coolest Linux based applications with Moblin SDK & win great prizes
Grand prize is a trip for two to an Open Source event anywhere in the world
http://moblin-contest.org/redirect.php?banner_id=100&url=/
_______________________________________________
Net-snmp-users mailing list
[email protected]
Please see the following page to unsubscribe or change other options:
https://lists.sourceforge.net/lists/listinfo/net-snmp-users