I was trying to figure out some port forwarding issues on my mother’s router (modem is already in bridge mode, before anyone suggests that) so I checked the IP addresses on the device. The IPv6 allocation was a /56 (as expected), so I went to the IPv4 address, and…
Either I’m reading this wrong or Spectrum has given out 8192 IPv4 addresses to one residential connection. For reference, Google Fiber hands out a /32, which is what I’d expect.
This was from a /14, so it’s not like the router is somehow displaying the direct allocation it’s part of.
Verizon Fios uses /24s (at least in my area). It doesn’t mean you can use more than one address. It’s just how they’ve designed their edge subnet.
/32 is more surprising to me as the ISP would need to burn 2 IPs per client since each has a dedicated gateway (although who knows what’s actually going on under the hood).
That would explain it. I’m not too familiar with how ISPs internally structure their networks and I couldn’t put together the right combination of search terms to find any info about this (especially since “19” in your search tends to make Google think “covid”). Spectrum handing out all those addresses for free seemed too good to be true.
The /32 is what shows up in WinBox, the ONT is a black box as far as I’m concerned.
It’s just the size of the subnet they are using for that layer 2 domain. They’re not giving you those address, that’s the network your WAN interface lives on.
So for example if your IP was 10.34.55.3/19 the network range of usable addresses for everyone on Spectrum in your area is 10.34.32.1 - 10.34.63.254. You just happen to have one of them, DHCP may give you a different one later on. If your neighbor reboots their modem, it might give them a different address in that range.
This size of subnet isn’t that crazy, maybe a little large, but not really.
Your Google Fiber box probably just mis reports it’s IP. Look for the subnet mask and you’ll find your true subnet. It probably says /32 (which is just a single address) since you are assigned just one, but you probably live inside of a /20 or /22 or /19 network or whatever your subnet mask tells you.
Also, as a side note, let’s say for just a minute that Spectrum really did give you a /19. What this actually means is that you can use that /19 INSIDE your network. The address on your WAN interface would NOT be inside the /19, it would be in a totally different network and would most likely be in a /29 or a /31 which is used a lot for point to point connections. Spectrum would then either route the /19 to your WAN address or you would advertise it via BGP to them (then they would advertise it via BGP to everyone else).
/32s work “fine”, even in case of ethernet if you expect to use it for point-to-point connections.
e.g. if you want this in Linux, you’d set your address to a.b.c.d/32 and the broadcast address to the x.y.z.w/32 and you’d get a working point to point ethernet route.
Re: /19
As @xradeon says, you got a single address out of /19 subnet. It means if you wanted to contact anyone else on the same subnet, the packet wouldn’t go through the upstream gateway, but the router would ARP request the mac address of the other host, and once it found it out, it would send the IP packet to that mac address directly.
