Comcast Public IP Addresses

Whiteout

Was trying to figure out some way I could get Comcast to give me a public/static IP address for "Educational purposes", well mostly educational

Any way I came across this and just made me curious:

"You can order Static IP addresses in blocks of 1, 5 or 13."

Any idea why they sell them in blocks of 13? Is that just a random number or is 13 something important in the world of networking that I don't know?

DPG

The blocks coincide with the size of the subnet that you are allocated.

/29 = 5 usable (8 - 1 network address - 1 broadcast address - 1 gateway address)
/28 = 13 usable (16 - 1 network address - 1 broadcast address - 1 gateway address)
/27 = 29 usable (32 - 1 network address - 1 broadcast address - 1 gateway address)
etc

You should learn about VLSM (Variable Length Subnet Masking) since it wasn't covered in ICND1.

Whiteout

So it's not just some random number, thanks DPG! Makes sense now, I will dig some more too

DPG

On a side note, I have noticed that Comcast usually uses the last available IP for the gateway.

For example:
100.100.100.0/29
Gateway is 100.100.100.6