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Old 02-01-2018, 02:19 AM   #1
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Registered: Feb 2018
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How to remove unused network Interfaces from SNMP Monitoring or IfTable

Hi ,

Our customer have a cron job running which restarts the snmpd during the scheduled task. As a result of snmp daemon restart , the customer receives a Link Down Trap as well . This confuses customer with a real Link Down event .

The reason for the link down error is that in the snmpd.conf file has following line which monitors the interface status.

defaultMonitors yes
linkUpDownNotifications yes

While customer uses eth0 , the other interfaces eth1 and eth2 are unused .

The IfTable lists the following :

IF-MIB::ifOperStatus.1 = INTEGER: up(1)
IF-MIB::ifOperStatus.2 = INTEGER: up(1)
IF-MIB::ifOperStatus.3 = INTEGER: down(2)
IF-MIB::ifOperStatus.4 = INTEGER: down(2)
IF-MIB::ifOperStatus.5 = INTEGER: down(2)

IF-MIB::ifAdminStatus.1 = INTEGER: up(1)
IF-MIB::ifAdminStatus.2 = INTEGER: up(1)
IF-MIB::ifAdminStatus.3 = INTEGER: down(2)
IF-MIB::ifAdminStatus.4 = INTEGER: down(2)
IF-MIB::ifAdminStatus.5 = INTEGER: down(2)

Can I configure the Iftable to remove the entries for eth1 and eth2 ? I do not want SNMP to monitor all the interfaces.

Just for additional Information ,here is what I found on Internet for the settings:

linkUpDownNotifications yes

This command enables link up and link down trap notifications, assuming the other trap configurations settings are set. This command configures the Event MIB tables to monitor the ifTable for network interfaces being taken up or down, and triggering a linkUp or linkDown notification as appropriate.

defaultMonitors yes

This command configures the Event MIB tables to monitor the various UCD-SNMP-MIB tables for problems (as indicated by the appropriate xxErrFlag column objects) and send a trap. This assumes the user has downloaded the snmp-mibs-downloader Debian package and comments out "mibs" from /etc/snmp/snmp.conf (as in: "#mibs").

Any help in this query will be very much appreciated.

Old 02-02-2018, 01:41 PM   #2
Registered: Oct 2009
Location: Colorado, USA
Distribution: I use Arch btw
Posts: 142

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This might be a long shot for you, but here's a potential solution based on the way my SNMP monitor works. I'll use examples from one of my Debian machines since it sounds like you're using Debian.

On a switch, there's a difference between a port being down (disconnected) and administratively down (disabled). I don't think the terminology is the same on servers, but the concept is.

For example, I have a network interface "enp2s0" with the following status. If I run "ifconfig" it appears, despite being physically disconnected.

If I run "ifconfig enp2s0 down", the interface no longer appears unless I use "ifconfig -a". To use switch terminology, this is the difference between being down and administratively down.

To keep the network interface administratively down after reboot, your /etc/network/interfaces entry should look like this:

iface eth1 inet manual
This should tell the Debian networking daemon to not automatically bring the interface up, but I haven't tested this. The also assumes you don't a GUI network manager superseding the configuration in your interfaces file.

In my SNMP monitor, this is what it takes to make it stop randomly notifying me that an interface is down. However, I don't use SNMPTRAP so this might not be useful to you at all.
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