Network Loop Detection

[jctech2025]

Hi All,

I recently Was working with Cisco Meraki support to troubleshoot a problem AP. We discovered it's gonna need to be replaced. However while looking into it, we ran a packet capture on the switch the ap is connected to and we noticed that there are thousands of frames being sent by netgear with RLDP loop detection packets. I had to install probably 150 netgear switches in the building because they went to VOIP for their phone system.

If I look at the capture in Wireshark I see, abbreviated:
Source - Netgear
Protocol - RLDP
Info - Network Loop Detection

Is this saying that a loop is being detected on the network, or that a loop is being looked for? I checked the manual for the switch and "Loop Detection" is from what I read disabled by default. There has been complains about latency in the building. I don't know that this would factor in, however I wanted to ask the community.

I'm also asking in the forum as the original capture was taken from the Meraki Dashboard.

Thoughts?

[Brash]

I don't have any Netgear switches but logically from what you're seeing, it sounds likely that the Netgear switches are sending broadcast frames for loop detection. The idea would be that if the same frame is then received on the port that originally sent it, there is a loop detected in the network. Similar to (or the same as) spanning-tree BPDU's.

Depending on how many broadcasts you have flying around, it's possible that could impact your network.

[jctech2025]

Yeah, this is the first I have heard about this type of broadcast.  I have tested from multiple devices and I am seeing the same traffic.  I'm trying to determine if it is a loop or if it is a check for a loop, either way it is the most traffic on the wire.  I have never had to log into one of these devices before either.

[jctech2025]

It appears that the switch has Loop detection enabled by default, however it also has Broadcast Filtering, which is not enabled.  Though it appears they both do the same thing?  Still trying to get this one down.

[Brash]

Broadcast filtering/storm control is a bit different. It's used to limit the amount of broadcast traffic that a given port will receive and process. This prevents broadcast storms from bringing down the network.

[jctech2025]

Ok, so the Loop detection is as the name implies, looking for the same frame on the same port?  So the broadcast filtering, would that be to limit the amount of packets being sent for detection?  Essentially to not overload how much can be processed on the port?

[jctech2025]

I have a case open with netgear as well, hoping I can determine the source/reason for the traffic.