1

There is an xfinitiwifi hotspot near me.

Comcast users ("slaves"?) can connect to xfinitywifi by entering their Comcast email and password on the browser redirect. Then it will record your MAC address and let you access later without the popup.

But the weird thing is, every time you login you get the IP address 192.168.1.10. Even if you login with multiple devices. (Also documented here: http://forums.comcast.com/t5/Home-Networking-Router-WiFi/What-Prevents-Xfinity-WiFi-Hotspot-Spoofing/td-p/2113294 )

How is it possible to have an access point reuse the same IP address for each client?

Improve this question

2 Answers 2

Reset to default
4

I suppose the AP could effectively put each associated client in its own VLAN, and not do intra-BSS relay. Then, somewhere on the network, they could run a separate NAT instance for each VLAN.

The only problem left to solve would be broadcasts from the network. If the router on one of the VLANs tries to send an ARP "who-has 192.168.1.10?" broadcast, all the clients would reply. But their replies would each go to a different VLAN, and all the ARP tables would be updated, making other VLANs' routers less likely to need to send ARP broadcasts as soon.

Alternatively, the network could employ other tricks to keep the ARP table up to date without requiring broadcast ARP requests from the router.

Honestly though, even though there are ways to make the network extra clever to make this work, I don't see why they'd go to these lengths.

Improve this answer
1
  • These VLANs seems like the correct explanation. Actually I'm surprised this isn't the default for all "hotspot" style wifi installations.
    – William Entriken
    Commented Apr 28, 2014 at 13:41
-2

A combination of vlans, tagging and mac/ip binding is what makes it work. I mean its only a class c ip with a prefix of /24.

The maximum number of VLANs on a given network is 4,094. Comcast generally issues Class B ip's 10.0.0.1/11 (255.224.0.0). Regardless each new client is assigned the necessary information via DHCP. However, the client was not only assigned an IP but also a virtual lan number. This isolates the vlan from everything except its gateway. The host can now assign the same lan segment and prefix (192.168.1.0/24) to each client as each vlan is autonomous of the other, except for its gateway. Finally, vlan tagging and arp binding provides routing for those clients who share the same class c ip address.

Improve this answer
4
  • how does this answer the question, ie "How is it possible to have an access point reuse the same IP address for each client?"?
    – Pierre.Vriens
    Commented Dec 7, 2017 at 21:46
  • While this may answer the question, it would be a better answer if you could provide some explanation why it does so.
    – DavidPostill ♦
    Commented Dec 7, 2017 at 22:05
  • The maximum number of VLANs on a given network is 4,094. Comcast generally issues Class A ip's 10.0.0.1/11 (255.224.0.0). Regardless each new client is assigned the necessary information via DHCP. However, the client was not only assigned an IP but also a virtual lan number. This isolates the vlan from everything except its gateway. The host can now assign the same lan segment and prefix (192.168.1.0/24) to each client as each vlan is autonomous of the other, except for its gateway. Finally, vlan tagging and arp binding provides routing for those clients who share the same class c ip address.
    – George Lawton
    Commented Dec 7, 2017 at 23:03
  • 1
    Great commentary, unfortunately your answer is next to useless, because it contains none of the information contained in your comment
    – Ramhound
    Commented Dec 8, 2017 at 0:22

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .