Why can I see non-broadcast traffic for other computers on LAN interface?
I have a simple setup of 3 computers connected with LAN cables to the same Asus RT-AX55 router.
I started a trace on computer2 but I can see traffic from the router intended for computer1. I am capturing on the standard Ethernet interface, the only one it has. The traffic isn't broadcast, in fact this is what one packet looks like:
Source Src Port Destination Dst Port Protocol Length Info
119.23.52.119 51413 computer1 55764 TCP 60 51413 → 55764 [ACK] Seq=1 Ack=1 Win=11944 Len=0
In the Ethernet part of the packet I can see the source is the router's MAC address.
How is this possible?
What is the "router", ideally the model number?
@grahamb, sorry - Asus RT-AX55, I'll add it to the question, as well.
So that's a home gateway, with WiFI access point, single WAN port and quad switched LAN ports. So from your perspective you're looking at a switch.
@Jaap, that doesn't make sense to me. The router is configured to be in a wireless router mode (I don't even know if it can be configured as a switch) and the total amount of packets, meant for computer1, that I've captured on computer2 is a tiny, insignificant fraction of the amount computer1 sent and received during the capture time.
Asus open source their code, if you really want to dig into what's happening.
The MERLIN project doesn't support the RT-AX55 but does list other
RT-AX
devices.