CenturyLink BRAS LAN Subnetting w/ Static IP

  • I’m not sure where this post should go so I’ll start here.

    Physical: Fiber > ONT > Ethernet > pfsense WAN

    I have a fiber connection that uses CenturyLink CBRAS aka BRAS. I have been using DHCP and Eero but want to change things up a bit. I got a static IP and attempted to use it. The tech says I am required to use the CL “modem” and configure “LAN Subnetting” on it.

    I want to do this without the CL HW if possible.

    I have already configured pfsense to get the DHCP address from CL and that works as I am online, but where do I configure the static IP? Here are the details I was given for ref.

    Static IP
    Network Address 71.33.xxx.72/30
    Router/Client 71.33.xxx.73
    Gateway 71.33.xxx.74
    Broadcast 71.33.xxx.75
    DNS 1
    DNS 2

  • You need to clarify with CLink how they want this done.
    With many providers, when you want a static IP, they require their own equipment to be in the path, and you then get a static IP behind it.

    If that's the case, their "BRAS" box would actually be 71.33.xx.74 (the "gateway"), and you'd set your pfSense WAN to use 71.33.xxx.73/30 (with a static default GW of .74). In this sort of situation, you'd probably want to change your "monitor IP" to something other than the gateway, because there's little point to monitoring a device that's just on the other end of your own c5e/c6 cable and on the same power as your router.

    This sort of thing is more common with the Telcos IME, but I've seen it with Comcast Enterprise (cable) as well. When you ask for a static, they take their coax modem/router device out of bridge mode and turn it into a router with a /30 facing you. If you request more IPs, they then just route a larger block to you over that /30 (so your router would get one side of the /30, and then they might issue a /29 or /28 with a bunch more IPs you can use on the "inside" of your own router).

  • Netgate Administrator

    They route the /30 to you via a dhcp address.

    You may be able to use the complete /30 as VIPs. Almost certainly both .73 and .74 but .72 and .75 might be available.

    Add them as IPAliases and test.


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