5 ms·

It's still not really modem-only mode. They do routing in there, mainly for their management layer.

Semaphor 5y ago
I must admit, I don’t know much about networking. But do you have some more information there? My German cable router is in modem-mode, and I’d be interested in knowing what kind of routing it still does.
- lxgr 5y ago
  DOCSIS networks usually assign some management IP address that the provider can access to perform remote diagnostics on the modem directly. It's usually invisible and inaccessible to the user. Also, in many cases there is a specific that the "modem" listens on, serving a web interface that allows switching back to "router" mode. This also wouldn't be possible with a "pure" modem (as it shouldn't have any concept of the IP layer).
  - Semaphor 5y ago
    That makes sense. After all, I weirdly had to use their webinterface to even put it into modem mode. Thanks. Though now that I’m thinking of it, are you sure it uses IP? It’s not as if they can’t use other layers.
    - LilBytes 5y ago
      Can't speak for all Telco's but in Australia, DOCSIS modems are registered by their MAC address on the modem it's self. Not by IP address. I can't imagine this is different else where so it's likely the replying comment above yours is incorrect. Source: I was previously a network engineer for a national Telco. Other sources: DOCSIS 3.0 registration info: https://volpefirm.com/docsis-3-0-cable-modem-registration/ https://volpefirm.com/docsis-3-0-cable-modem-registration/
      - dangerface 5y ago
        Virgin used to just use the mac address with their old modems, you could flash the firmware and change the mac so you could buy their cheapest package and flash the mac of a modem with unlimited gbit internet. They craked down on that a few years ago tho so I don't think this is possible anymore.
        lxgr 5y ago
        Modern DOCSIS also uses certificate-based authentication. Only the owner of a given MAC OUI is able to create a certificate covering MACs under it that will be accepted by the CMTS.
      - lxgr 5y ago
        Registration/network access and management are two different things, no?
        LilBytes 5y ago
        Not always, with Telstra the MAC address was also responsible for authentication. Though I believe it's since changed, my last interaction with DOCSIS was 4-5 years ago. I seem to recall there's a captive portal involved now but previously it was solely MAC.
  - thrashh 5y ago
    Note that even many actual DOCSIS modems have management interfaces and are not pure. I have always been able to view the management page for my Arris/Motorola Surfboard modems.
gruez 5y ago
But that's fine right? If your ISP wants to send you bad packets having your own equipment isn't going to stop them either

I must admit, I don’t know much about networking. But do you have some more information there? My German cable router is in modem-mode, and I’d be interested in knowing what kind of routing it still does.

lxgr 5y ago
DOCSIS networks usually assign some management IP address that the provider can access to perform remote diagnostics on the modem directly. It's usually invisible and inaccessible to the user. Also, in many cases there is a specific that the "modem" listens on, serving a web interface that allows switching back to "router" mode. This also wouldn't be possible with a "pure" modem (as it shouldn't have any concept of the IP layer).
- Semaphor 5y ago
  That makes sense. After all, I weirdly had to use their webinterface to even put it into modem mode. Thanks. Though now that I’m thinking of it, are you sure it uses IP? It’s not as if they can’t use other layers.
  - LilBytes 5y ago
    Can't speak for all Telco's but in Australia, DOCSIS modems are registered by their MAC address on the modem it's self. Not by IP address. I can't imagine this is different else where so it's likely the replying comment above yours is incorrect. Source: I was previously a network engineer for a national Telco. Other sources: DOCSIS 3.0 registration info: https://volpefirm.com/docsis-3-0-cable-modem-registration/ https://volpefirm.com/docsis-3-0-cable-modem-registration/
    - dangerface 5y ago
      Virgin used to just use the mac address with their old modems, you could flash the firmware and change the mac so you could buy their cheapest package and flash the mac of a modem with unlimited gbit internet. They craked down on that a few years ago tho so I don't think this is possible anymore.
      - lxgr 5y ago
        Modern DOCSIS also uses certificate-based authentication. Only the owner of a given MAC OUI is able to create a certificate covering MACs under it that will be accepted by the CMTS.
    - lxgr 5y ago
      Registration/network access and management are two different things, no?
      - LilBytes 5y ago
        Not always, with Telstra the MAC address was also responsible for authentication. Though I believe it's since changed, my last interaction with DOCSIS was 4-5 years ago. I seem to recall there's a captive portal involved now but previously it was solely MAC.
- thrashh 5y ago
  Note that even many actual DOCSIS modems have management interfaces and are not pure. I have always been able to view the management page for my Arris/Motorola Surfboard modems.

gruez 5y ago

But that's fine right? If your ISP wants to send you bad packets having your own equipment isn't going to stop them either