Client names mappings incorrect for devices behind a repeater (shared MAC)

[thr-4]

Versions

• Pi-hole: 6.4
• Web: 6.4.1
• FTL: 6.5

Platform

• OS and version: Debian Bullseye

• Platform: Raspberry Pi

Expected behavior

Name defined in Local DNS should only be mapped to the client with specified IP address, not to all devices with the same MAC address (behind a repeater).

Actual behavior / bug

All devices behind my repeater are seen by the system that pihole runs on as having the same MAC address. Only one of these devices (which has a static IP) has a "friendly" name, defined in Local DNS settings.

Pihole propagates this name to all devices behind the repeater (see screenshots).

Steps to reproduce

Steps to reproduce the behavior:

1. Add a Local DNS entry
2. See the name mapped to all IPs behind the repeater (shared MAC address)

Debug Token

• URL:

Screenshots

[yubiuser]

What happens if you add another Local DNS record for one of the devices with the 'wrong' assignment?

[thr-4]

@yubiuser I have added a Local DNS record for a second device with a static IP and, unfortunately, after a while, the same thing happens - the names propagate randomly across the IP adresses that are "mapped" to the repeater's MAC, creating duplicate names in the client lists.

[rdwebdesign]

Please generate and post a debug token:

• run pihole -d command.
• when asked to upload the log, answer Y.
• copy only the token and paste here.

[thr-4]

@rdwebdesign https://tricorder.pi-hole.net/OSBSLCz5/

[rdwebdesign]

Note:

You don't need to mention us when you answer. We are already notified every time a comment is written here.

[thr-4]

FYI, here is the screenshot from the Network overview for the cluster of devices behind the repeater's MAC address, from a different pihole on the same network and the same single Local DNS record for the NAS. The NAS with IP address ending with .125 has the correct name assigned to it, but the same address is assigned to a different device (.174), and there are also other IPs mapped incorrectly to pi.hole name. There are no relevant /etc/hosts entries in either case.

[yubiuser]

I'm going to label this as bug, as it seems assigning the same name to multiple IPs (despite same MAC) seems to be the wrong behavior.

What kind of repeater is this? Is it capable to send EDNS0 information?

[thr-4]

It’s a rather basic TP-Link (https://www.tp-link.com/au/home-networking/range-extender/re450) used in pure repeater/extender mode, my main router is the DHCP server.

[DL6ER]

Could you please enable debug.database, e.g. via

sudo pihole-FTL --config debug.database true

or via the web interface, environment variable?

Then please flush the network table cache, e.g., via this button:

Then, please restart pihole-FTL and, as soon as the issue starts showing up again, upload the log. You can use

cat /var/log/pihole/FTL.log | pihole tricorder

to securely upload this to a place where only Pi-hole developers can access it. In this case, you'd need to provide the debug token you'll receive in reply to this command (you may or not need sudo for this, depending on the permissions of your login user)

[thr-4]

Done, have uploaded the log the moment the duplicate device started to appear.

https://tricorder.pi-hole.net/dkVjlout/

[rdwebdesign]

Can you please tell us the device name/IP?

This log is huge and the name and IPs would help us search for the issue.

[thr-4]

The device the pi-hole runs on is 192.168.0.102. The device that has a Local DNS record and whose name got incorrectly propagated to all IPs behind the repeater is the thr-ds1.lan device (which has a Local DNS record of 192.168.0.186), see screenshot. The MAC address of the repeater starts with 5a:72:8b:xx:xx:xx.

Edit: initially, the thr-ds1.lan name was correctly assigned to 192.168.0.186 only. The incorrect names started appearing approximately 30-60 minutes after FTL restart and Network table flush.

[DL6ER]

Okay, thank you. I guess the reason why the multiple MAC addresses happens is clear, if not, let me quickly summarize it here. If you know this already just skip the rest of this and continue reading behind the horizontal divider below:

Networking operates in layers, and MAC addresses and IP addresses live in different worlds:

• Layer 2 (Data Link): This is where MAC addresses live. They only have meaning within a single broadcast domain (e.g., your local Wi-Fi or the switch connecting your home devices).
• Layer 3 (Network): This is where IP addresses live. IP addresses are designed to be "end-to-end," meaning they persist across different networks.

When data moves from one network to another, it has to pass through a router. A router's fundamental job is to strip off the Layer 2 frame (containing the MAC addresses) from an incoming packet, inspect the Layer 3 header (the IP address), and then create a new Layer 2 frame for the next hop.

You could also think of the data being carried inside a series of envelopes. When your device sends data, it wraps it in an envelope addressed to the router’s MAC address. The router opens that envelope, sees the data is meant for the internet, and throws away the outer wrapper (your device's MAC address). The router then puts that same data into a new envelope and addresses it to the MAC address of the next device (the ISP's gateway). Because that original envelope (with your device's MAC address) is discarded at the router, the rest of the world never gets to see it.

---

The solution for me seems to be modifying the mechanism we use to obtain hostnames from devices when there is no other source of information. The change that'd be needed seems rather simple to me: Discarding host names obtained by MAC address when the MAC address appears multiple times (suggesting a router being in place). Does that sound useful?