Given a block of public IP addresses by my ISP. What now?

Installing and Using OpenWrt
1

I'm behind a large ISP CGNAT and I requested a block of 4 public IP addresses for my connection. They sent me back a block of 4 public IPs with only the two IP addresses in the middle as usable (below is an example not using the real IPs)

100.64.0.3, 100.64.0.4, 100.64.0.5, 100.64.0.6

They also sent me some updated static IP settings for the router consisting of private IP space:

WAN IP: 10.20.20.21/29
Gateway: 10.20.20.20

I've set the static IP setings for the router but when I check my public IP using whatismyip, it doesn't return an IP in my public IP block.

I'm sure I'm missing something here, I did try the instructions on the OpenWRT guide here but in 19.0.4, Luci informed me that the configuration needed to be updated in some way and my connection stopped working.

3

I don't think you can use those IP's on your outgoing packages if behind CGNAT

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4

I think they've done some kind of mapping between those internal IPs and the public IP block.

They showed me a sample Cisco configuration where a public IP was set as a "secondary IP" or something along those lines but I wasn't sure how that would translate to OpenWRT.

5

Sounds like some kind of mapping, but you should tell us their verbal advice/docs, if they have provided you anything. Based on just those addresses it is pure guessing what they are actually providing.

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6

They haven't given us anything beyond that and showing us a sample Cisco config (that we couldn't take a picture of)

I'm wondering if anyone has seen something similar elsewhere and had any ideas.

7

I assume the public IP belongs to the ISP not you and they are port forwarding to your static WAN IP.

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8

Yes, that would make sense and I assumed that the mapping would happen naturally once those WAN IP settings on the router were set but it seems like there might be some additional configuration needed.

9

I don't think whatismyip is a good test.

You need to open a port or forward locally to a server and test if you can reach from outside your network

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10

I get lost with that. They briefly showed you something and you were supposed to memorize the needed config?

11

They basically showed me a config that was irrelevant to me (someone else's Cisco settings) and said 'See, it's possible'

There's no other ISP so it's not like I can go elsewhere.