SNMP byte counters on an AC1900P (RT-AC68U)

[JefferMC]

Tagging and logical interfaces would seem to be two different things. I would expect the logical interface to exist and the counters to be collected. IIRC, VLAN2 shows up if you turn on the IPTV feature as that seems to be implemented as a VLAN.

 

[drinkingbird]

Tagging and logical interfaces would seem to be two different things. I would expect the logical interface to exist and the counters to be collected. IIRC, VLAN2 shows up if you turn on the IPTV feature as that seems to be implemented as a VLAN.

You have to tag it at layer 2 in order for a logical interface at layer 3 to see it (whether it be an eth0.2 subif or a vlan2 software interface).

If you use the IPTV settings that means your ISP supports 802.1Q vlan tagging (or rather, requires it) so in that case they can tag stuff on the WAN. VLAN 2 would get used if you specify that for the internet portion. If internet is vlan 1 they are likely still using the same model of stripping the tag off before it goes out the WAN port, and may still use the same model where there is no L3 vlan2 interface.

There are probably better ways they could have implemented it but I'm guessing they did not want to use VLAN 1 for the WAN for security reasons which requires some workarounds.

 

[JefferMC]

This looks worse than it is, due to offsets in the collection; low one interval, then catches up the next (or vice versa).

I have an expensive switch with SNMP that I could just create a two-port VLAN on and pass the data through it, but it's really not worth that. I get that this is a consumer router, but basic interface counters didn't seem to be a big ask.

And, IMHO, interfaces are a layer 2, not a layer 3, thing. Bytes flowing through a layer 2 interface can be counted. The above mentioned switch provides counters for every single port whether or not it's tagged, or whatever the layer 3 protocol might happen to be.

 

[drinkingbird]

View attachment 49017
This looks worse than it is, due to offsets in the collection; low one interval, then catches up the next (or vice versa).

I have an expensive switch with SNMP that I could just create a two-port VLAN on and pass the data through it, but it's really not worth that. I get that this is a consumer router, but basic interface counters didn't seem to be a big ask.

And, IMHO, interfaces are a layer 2, not a layer 3, thing. Bytes flowing through a layer 2 interface can be counted. The above mentioned switch provides counters for every single port whether or not it's tagged, or whatever the layer 3 protocol might happen to be.

Smart/managed switches have interface counters. Dumb switches don't.

 

[JefferMC]

Even as stripped down as it is, you could not possibly confuse this router with a dumb switch.

 

[drinkingbird]

Even as stripped down as it is, you could not possibly confuse this router with a dumb switch.

Hate to break it to you but the 5 ports on the back are just a 5 port switch with some software based VLAN tagging functionality. A single backplane uplink from there to a software based router. It is a really inexpensive Linux box with a 5 port cheap switch hanging off it.

 

[JefferMC]

VLANs on a single switch do not require tagging, at least on real switches. I suppose this lightweight SoC implementation puts tags on them so it can deal with it?

 

[drinkingbird]

VLANs on a single switch do not require tagging, at least on real switches. I suppose this lightweight SoC implementation puts tags on them so it can deal with it?

Unmanaged switches do not support VLAN tagged frames. They won't even pass them. Different ethertype and they exceed standard frame size. There are some unmanaged switches out there that will pass them but they are are fairly uncommon and a bit of a hack.

I don't know the exact architecture of the switch in these routers, they do have some sort of vlan tagging/reading ability but it is very basic. Considering a $15 5 port switch can do full vlan tagging, port mirroring, QOS, etc, that means these routers have about a $5 switch in them. You typically need a full fledged managed switch for SNMP port counters etc.

The fact that many routers require hardware acceleration to be disabled to do VLAN tagging on the switch ports tells me they don't even have their own intelligence, they are relying on the SOC's CPU to even do the tagging function.