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Comment by nitrogen | Hacker News Reader

It's not just about inbound connections, people also generally don't want to have their outbound devices clearly visible by counting unique IPs, or MAC addresses (and thus manufacturer) of devices sent out with every packet when MAC is used to generate the address, or another globally unique identifier for ad networks to track.

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I think all major OSes have privacy extensions enabled by default, and therefore use random addresses that change regularly.

They 100% most certainly don't. I would have no idea what anything is on my network if every workstation's MAC addresses was constantly changing. Some OS's do randomize per SSID, but it doesn't constantly change, it would break DHCP by using up all the addresses. You can't just constantly change your L2 address.

This is in IPv6, not v4. I highlight that because you mention DHCP, which generally isn’t used there. And it’s not the MAC address that changes, but the 64-bit interface identifier. Ethernet would probably stop working if the MAC address changed with any regularity. You can read more about this at https://www.internetsociety.org/blog/2014/12/ipv6-privacy-ad...

From that article written in 2014, these OSes have privacy extensions enabled by default:

- All versions of Windows after Windows XP

- All versions of Mac OS X from 10.7 onward

- All versions of iOS since iOS 4.3

- All versions of Android since 4.0 (ICS)

- Some versions of Linux (and for others it can be easily configured)

With IPv6 and SLAAC your external IPv6 address changes on a schedule using privacy extensions...

Mine at home is configured to change every 30 minutes.

As sibling points out, that’s already covered by the IPv6 privacy extensions, which every major OS has some support for [1]

1: https://datatracker.ietf.org/doc/html/rfc4941

This is why I haven't swapped, but I didn't realize they've accounted for this at the client level. Makes sense, still makes me think about IoT devices though and things I don't have 'control' over like my chrome cast.

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