Not 100% sure but TR-069 might be the standard involved that is allowing your ISP to access your CPE (modem/router) and get information from it. Probably all DSL modems you buy and certainly any you get from the ISP will be TR-069 enabled.
I have cable (DOCSIS) and bought my own modem, without a built in router, and then bought a separate router. This is ...
Do not tamper with the contents of /System. They are managed by the operating system, and modifying them will cause problems.
In this case, removing this keychain is likely to cause most secure network requests -- including ones made internally by the operating system -- to fail. It may also interfere with code signing, which may make your computer ...
About "bridge mode"
"Bridge mode" on ISP "router" is important if You get Public IP from ISP.
It allow to install this Public IP on Your router WAN port.
And if You ask You ISP about it, ask something like:
"I want to set my public IP on WAN port of my router, how it possible?"
Bridge mode can be useful on some ADSL/cable modems-routers, which CPU ...