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SNMP issues

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SNMP issues

I've got MRTG monitoring about 20 nodes in our mesh network via SNMP. We're running ver  I'm seeing some unusual things I can't figure out.  I can't find much information about what OIDs are available, so for now I'm just looking at interface traffic byte counts.  Here's what I think I know about the interfaces on an AirGrid M2 HP:

  • Interface 1 lo - Loopback port
  • Interface 2 eth0 - Untagged LAN port traffic (and possibly includes tagged VLAN 1 and 2 traffic)
  • Interface 3 (no name) - interface is down
  • Interface 4 eth0.2 - VLAN 2 d2d port traffic
  • Interface 5 eth0.1 - VLAN 1 WAN port traffic
  • Interface 6 (no name) - Wireless port traffic
  • Interface 7 wlan0-1 - Possibly all receive wireless traffic - only shows inbound counts, and shows more traffic than interface 6.

The first problems I run into are interface 6 has no name, and both interface 6 and 7 both report an ifSpeed of 0, which causes tools like MRTG to ignore them.
The next unusual thing is most of the time when there is any significant traffic, the in and out byte counts on most of the interfaces are identical (the blue 'out' line matches the green 'in' line:

But not always:

I'm having trouble interpreting what I'm seeing.  Can anyone shed some light? 
I'm pretty sure the lack of a description for interface 6 and the ifSpeed=0 issues are bugs.  The matching in/out byte counts do not seem right either.

John N9ZL

AE6XE's picture

The AirGrid has 1 physical port as I recall.    Be careful on some devices with 2 ports, and particular the AirRouter and the NSM5 XW which also have an internal switch.    You will see empty interfaces that do physically exist, but are unused by AREDN.  

eth0:   LAN interface for laptops, voip, etc. in AREDN.  Represents an interface (a physical Ethernet port in our case).   When 802.1q vlan tags are on packets, and are in use in AREDN, eth0 can exist along with "eth0.0" -- no tag vs a tag of '0' on the packet.   I have seen driver implementations show 2 interfaces "eth0" and "eth0.0", but only 1 is active/selected as the LAN interface.  If this happened, SNMP would also show an unused interface.  Probably what you are seeing.

If you obtain command line access, do the "ifconfig" command and you can see more details on each interface SNMP is reporting.

wlan0-1 is a 'monitor' interface for the wireless interface.  It will show different stats and is for diagnostic purposes.  Some packets are not passed up the protocol stack to the wlan0 interface if they are out of scope for how it is configured.


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