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Why does the VDX send SNMP interface status related traps for events that don't show up in "show logging raslog" for interfaces that don't show up in "show interface"?

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TitleWhy does the VDX send SNMP interface status related traps for events that don't show up in "show logging raslog" for interfaces that don't show up in "show interface"?
Question
Why does the VDX send SNMP interface status related traps for events that don't show up in "show logging raslog" for interfaces that don't show up in "show interface"?

While SNMP interface status traps may not contain explicit interface names, they do contain ifIndex numbers that can be used with "snmpwalk" of ifDescr to determine interface name. When the VDX sends an SNMP interface status without recording anything in "show logging raslog", the interface name that can be determined from the ifIndex with "snmpwalk" is not one that shows up in "show interface".

For example, say a VDX sends a trap with the following information even though nothing is recorded in "show logging raslog".
DISMAN-EVENT-MIB::sysUpTimeInstance 404:7:12:07.00
SNMPv2-MIB::snmpTrapOID.0 IF-MIB::linkDown
RFC1213-MIB::ifIndex.805306372 805306372
RFC1213-MIB::ifAdminStatus.805306372 down
RFC1213-MIB::ifOperStatus.805306372 down
SNMPv2-MIB::snmpTrapEnterprise.0 Brocade-REG-MIB::bcsiReg.3.1.131

"snmpwalk" will show that the ifIndex corresponds with an interface named tunl0.
$ snmpwalk -v 2c -c public 10.170.104.26 ifDEscr | grep -A 6 805306369
IF-MIB::ifDescr.805306369 = STRING: lo
IF-MIB::ifDescr.805306370 = STRING: eth0
IF-MIB::ifDescr.805306371 = STRING: eth1
IF-MIB::ifDescr.805306372 = STRING: tunl0
IF-MIB::ifDescr.805306373 = STRING: gre0
IF-MIB::ifDescr.805306374 = STRING: sit0
IF-MIB::ifDescr.805306375 = STRING: port0

The interface tunl0 shows up in "snmpwalk", but it is not one that shows up in "show interface".
Environment
  • VDX any platform
  • Any version of NOS software
Answer
The VDX Network Operating System uses a Linux-based operating system at its core. It includes many Linux default system interfaces as part of this core. These interfaces have only an internal, virtual, system-level existence. They have no physical existence. They cannot be seen in the standard NOS CLI command "show interface", but their internal existence can be confirmed with the command "oscmd ifconfig".

For example:
VDX1# foscmd ifconfig tunl0
tunl0     Link encap:IPIP Tunnel  HWaddr
          NOARP  MTU:1480  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0

VDX1# foscmd ifconfig gre0
gre0      Link encap:UNSPEC  HWaddr 00-00-00-00-05-24-3F-BD-00-00-00-00-00-00-00-00
          NOARP  MTU:1476  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0

VDX1#

The VDX implementation of SNMP uses an snmpd that is based upon the SNMP daemon found in many Linux-based operating systems. This implementation includes monitoring of Linux default system interfaces that can be seen with "foscmd ifconfig" but not with "show interface". When the snmpd daemon becomes briefly and intensely busy, it can temporarily fail to monitor Linux default system interfaces. Snmpd interprets this temporary failure to monitor as an interface going down and up, and it sends traps accordingly.

As long as no corresponding event shows up in "show logging raslog", these false traps can be safely ignored.
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