Is the Modem's MAC Address Public?

2

Just reading about tracking and security. So far from resources I gather that the MAC address of my machine is known to the router and when the router communicates with the modem the MAC address of the router is passed and the machine's MAC address is lost. But after that, when an IP connection is made, what happens to the modem MAC address? The ISP gets the information as it should (for billing and tracking) but after that does it communicate that to the websites so they might track me via Router MAC address? Also even after using the VPN is the modem MAC address communicated to the other sites, or does just VPN provider see it and pass on its own MAC when communicating with other sites?

Saurabh Sharma

Posted 2015-06-23T16:39:21.700

Reputation: 21

Question was closed 2015-06-24T23:19:09.497

Answers

2

No, MAC addresses are Ethernet hardware addresses, and don't leave the immediate Ethernet LAN. As your packet goes through an IP router/gateway, the previous MAC address is stripped off and new link-layer addresses are added as necessary for whatever link-layer technology is in use for the next hop of the network path.

So while your ISP's first-hop router (e.g. DSLAM or DOCSIS CMTS) might be able to see the MAC address of your modem, the next hop router after that (still within your ISP) will only see your IP address.

That said, if you run some software on your machine that has access to read your MAC address, it might read it and report it as part of the payload of a packet, if it wanted to track you.

Spiff

Posted 2015-06-23T16:39:21.700

Reputation: 84 656

Nor are MAC addresses unique – mpez0 – 2015-06-23T17:45:18.097

1@mpez0 What do you mean? MAC addresses are generally unique. – Spiff – 2015-06-23T18:30:44.430

Default MAC addresses are unique, but MAC addresses can be changed on the fly. Some network protocols (e.g., DECNet) set MACs directly. Some topologies work better if all interfaces on a given host have the same MAC. MACs on the wire are not unique. Look up SIOCSIFHWADDR. – mpez0 – 2015-06-24T13:53:21.493

@Spiff Thanks for the clarification. " if you run some software on your machine that has access to read your MAC address, it might read it and report it as part of the payload of a packet, if it wanted to track you." yeah this part i Know just wanted to confirm about the router Mac being carried forward which you cleard :). Thanks – Saurabh Sharma – 2015-06-24T19:25:02.553

Asked: 2015-06-23T16:39:21.700

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Active: 2015-06-23T17:17:28.337