Supposing, we have following pieces in a theoretical network architecture

  • Network A: A low power IPV6 wireless network
  • Some low power hosts: Low power devices which are connected to the above low power IPV6 wireless network.
  • Network B: a Wi-Fi Network
  • A border Router which is connected to a Wi-Fi AP and also part of the low power IPV6 wireless network.
  • Some Wi-Fi stations: which are connected to the same Wi-Fi AP, to which border router is connected.

Considering above architecture, The border router enables bi-directional IP connectivity between these two different networks. In such setup, when a host in Wi-Fi network wants to reach to one of the hosts in the Lowe power IPV6 network, what will be sequence of packet flow?

For example, the 'Host x' in Wi-Fi network wants to send a packet to 'Host x1' in low power ipv6 network, will following be the packet sequence?

Host x -> Wi-Fi AP -> Border Router -> Host x1 .

Is above correct? if yes, How Wi-Fi AP knows which device it should forward the packet to? or how does it it know that, it should forward the packet which is destined for 'Host x1' to the Border router only? Which information's are required by the Wi-Fi AP to know before hand for getting this to work?

Or if the sequence of packet flow is incorrect, please suggest what will be the correct flow or sequence of packet transmission.

  • do you know how is border router connected to AP?
    – Effie
    Oct 7 at 10:08
  • Well not very sure about it. I just connected it to the AP via some command line test tool, which scans the AP and connects to it using just SSID and passphrase, in the similar way I connect the other Wi-Fi stations like mobile phone. I am not sure about internals. Could you help explain it. Oct 7 at 11:02

The router has two interfaces— one on each network. Each host is configured with the default gateway set to the address of the router interface.

Traffic to the other network will be sent to the router, which will forward it to the destination.

Note that the Ip packet has the destination address of the host, and that never changes.

  • apparently this "border router" does not have to be a router, it can act as a bridge (to the non-LoWPAN network part): zaidmufti.wordpress.com/2016/09/24/what-is-6lbr
    – Effie
    Oct 7 at 10:15
  • 1
    @Effie the issue it that the term "network" is ambiguous. It can be used to speak about a worldwide company infrastructure, a site, a layer 3 segment, or a layer 2 segment (and many other things like a VLAN, an IP subnet...) In this case we need to distinguish if the 2 "networks" are 2 distinct layer 2 segments with routing between them or a single layer 2 segment which would indeed require a bridge and not a router.
    – JFL
    Oct 7 at 10:26
  • a term border router is specific to LoWPAN network, and it is pretty specific what this is. and i don't think wi-fi network generally refers to a mesh.
    – Effie
    Oct 7 at 10:33
  • @Effie, thanks for sharing this article - zaidmufti.wordpress.com/2016/09/24/what-is-6lbr . The setup shown as example is similar to what I am using. A low power (802.15.4) network on one side and WiFi network on the other side. I can see two interfaces on my BR device , one is wpan0 and another is wlan0. But, the BR in my case is separating into two completely different subnets in my opinion. Is this assumption about packet delivery from Wi-Fi station to low power host correct? Host x -> Wi-Fi AP -> Border Router -> Host x1 . Oct 7 at 11:11
  • i think this video should give more detail: youtube.com/watch?v=LuCuxIdl8ls. I think these different modi depend on what your Wi-Fi AP supports. In most simple case the prefix of LoWPAN should belong to the same subnet, and then BR acts like a transparent or smart bridge. If you sill have question, could you update the original question with them? Depending on what Wi-Fi AP is the question is too general to answer. Also, you probably can check the assigned addresses and see whether they are in the same subnet or not.
    – Effie
    Oct 7 at 11:23

I don't think there is a general answer to this question without knowing what functions (besides Wi-Fi) does Wi-Fi AP have. Here are some anchor points for the answer, so they do not exist in comments.

Border router can be different things, and depending on that, there are different ways deviced decide how to forward packets. I found these references which explain it (somewhat):

  • 6LBR Modes
  • Video (i think it explains the same pictures, but it gives some details about how things work with these modi.)

The pictures in the references show border router connected to a switch which is connected to a router which is connected to internet.

If you have a home router, then most likely it will be a single box which

  • is is one box that is both the router and the switch
  • is the one that assigns prefixes

In IPv6 devices can autoconfigure themeselves by asking routers to assign them IP addresses (it can be either part of IP neighbor discovery, or DHCPv6).

Then your BR will most likely be a smart bridge. I think in this case your LoWPAN addresses will belong to the same subnet as the hosts themeselves. You can probably check this.

Actually, i am not sure that two devices in the same Wi-Fi network (the same SSID) need the Wi-Fi AP to communicate. In theory they can communicate directly. Also in theory without further configuration this will only work if addresses are in the same subnet.

P.S. you probably should begin with figuring out how does the host knows an IP address of your LoWPAN device. It may tell you what other stuff needs to happen, before they can actually talk to each other.

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