Hello guys, i'm attempting to monitor a TP-Link ER605 Multi-WAN VPN Router via SNMP, but I'm encountering an issue with the third WAN interface (WAN3) not exposing traffic statistics through the standard SNMP MIBs.

 

The ER605 is configured with three active WAN connections:

• WAN1 (Port 1): 192.168.10.99/24 → Gateway 192.168.10.1
• WAN2 (Port 2/WAN/LAN2): 192.168.5.100/24 → Gateway 192.168.5.1
• WAN3 (Port 3/WAN/LAN3): 192.168.1.97/24 → Gateway 192.168.1.1

All three links are active and routing traffic (visible in the Omada Controller web interface).

 

When querying traffic statistics via SNMP for WAN1 and WAN2, I successfully receive data:

 

# WAN1 (interface index 1041)
snmpget -v2c -c public 192.168.0.1 .1.3.6.1.2.1.31.1.1.1.6.1041
# Returns: Counter64: 39084160173

# WAN2 (interface index 1042)
snmpget -v2c -c public 192.168.0.1 .1.3.6.1.2.1.31.1.1.1.6.1042
# Returns: Counter64: 35941880609

However, when querying WAN3 using the same method:

# WAN3 (interface index 1043)
snmpget -v2c -c public 192.168.0.1 .1.3.6.1.2.1.31.1.1.1.6.1043
# Returns: No Such Instance currently exists at this OID

Through SNMP walking and analysis, I've confirmed:

 

The IP address exists in the IP Address Table:

.1.3.6.1.2.1.4.20.1.1.192.168.1.97 = IpAddress: 192.168.1.97
. 1.3.6.1.2.1.4.20.1.2.192.168.1.97 = INTEGER: 18

This indicates WAN3 is assigned to interface index 18 (SNMP index 1025+18=1043).

 

The gateway is reachable in the ARP table:

.1.3.6.1.2.1.4.22.1.3.18.192.168.1.1 = IpAddress: 192.168.1.1

 

Routing table entries exist for the 192.168.1.0/24 network.

 

Physical interfaces detected via SNMP:

iso.3.6.1.2.1.2.2.1.2.1026 = STRING: "default/eth0"
iso.3.6.1.2.1.2.2.1.2.1027 = STRING: "default/eth1"

 

No "eth2" or similar interface is listed, suggesting WAN3 might be implemented as a sub-interface, VLAN, or virtual interface.

 

Is this expected behavior for the ER605 when using three WAN ports? Does the third WAN use a different SNMP structure?

Are there alternative OIDs or private MIBs (TP-Link enterprise MIBs) that expose WAN3 traffic statistics?

Could WAN3 be sharing the physical interface with WAN2 (port multiplexing/trunking), making individual traffic counters unavailable via standard SNMP?

Is there a firmware limitation preventing SNMP monitoring of the third WAN port?