Subj : A small questionary on ISPs
To   : Scott Street
From : Victor Sudakov
Date : Sun Oct 24 2021 13:26:34

Dear Scott,

23 Oct 21 15:24, you wrote to me:

 SS>>>     inet6 2601:48:c500:9340::c0e3 prefixlen 60 dynamic

 VS>> This is very interesting. Why "prefixlen 60" on the LAN?

 SS> Perhaps - an educated guess here - Comcast's provided gateway has,
 SS> potentially, 4 internal LAN interfaces.  It could be configured with a
 SS> 5GHz WiFi subnet, a 2.4GHz one, the GbE ports, and a 'Xfinity Home'
 SS> port.   I haven't investigated what the "Home" port is used for, but
 SS> that may explain the breaking down of the /64 to /60.  Again, just a
 SS> theory.

Whatever Comcast's intentions, are you sure that a LAN with a prefixlen different from /64 will work properly? Will a non-standard prefix not break SLAAC and other things?

This is where my theoretical knowledge is lacking, but I've always been warned against using anything different from /64 on a LAN segment.

Victor Sudakov, VAS4-RIPE, VAS47-RIPN
--- GoldED+/BSD 1.1.5-b20170303-b20170303
 * Origin: Ulthar (2:5005/49)

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