Guest network with Public IP addresses!

[Moudar]

Hi 

I was in a restaurant which is like Mcdonald and there they have a Cisco AP with open guest network.

What was weird for me is that my mobile phone was getting public ip addresses from the AP (DHCP) like: 78.64.51.208 or 78.64.41.51

(I tested different mobiles)

Can someone who knows explain how does this work?!  specially if there are many guest users.

What i know is that the AP will check with the WLC and share any private IP pool (DHCP) with the users!

[Scott Fella]

Keep in mind that maybe… maybe… they used public ip space behind a nat. You are not limited to use private ip space when configuring a dhcp pool nor interfaces. I have seen that used in the past

[Moudar]

If that was the case (using public ip space behind a nat ) is there any benefit by doing that?

[Scott Fella]

You must ask yourself why would you? You have to make sure that is not routing outside your network since you don’t own it. Now it’s different if you own a large chunk and want to waste them for users… not really a good idea.

[Rich R]

No benefit and you shouldn't do it because it will break any real internet service on those IP addresses.

It's also possible (but very unlikely) that they actually own a block of public IPs which they're using for that but that would be very wasteful of valuable IPs.

That block is registered to Telia in Sweden:

% Information related to '78.64.0.0/12AS3301'

route: 78.64.0.0/12
descr: TELIANET-BLK
origin: AS3301
mnt-by: TELIANET-RR
created: 2007-03-16T08:55:19Z
last-modified: 2007-03-16T08:55:19Z
source: RIPE

"What i know is that the AP will check with the WLC and share any private IP pool (DHCP) with the users!"
The AP doesn't "check" anything - it simply forwards client DHCP requests which a DHCP server responds to whether that's locally, on WLC or remote via DHCP relay or proxy.

[Moudar]

Telia is the biggest ISP in Sweden, maybe it is Telia that operates the network on that restaurant.

[Rich R]

If it's a Swedish location then yes that is possible, in which case it's just a waste of IP addresses.