Behavior of the Mobile Node

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Titre du projet VoIP et Mobilité IPv6
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Page principale Projet de spécialité VoIP et Mobilité IPv6

Here we present the results of our (short) experiments about the behavior of the Mobile Mode (MN), in different situations.

Mobile Node in Home Network

When the mobile node is in its home network, its address is logically its home address: Hence, communications from and to the mobile node happens exactly as for any device: the mobility mecanisms are not used in that case.

Mobile Node in a Visited Network

Triangle routing configuration

Reminder: According to the Mobile IPv6 specifications, the Mobile Node should be reachable at its home address, even when it is in a visited network; Let us detail the mecanism allowing this.

  1. The MN is connected to a foreign network
  2. MN catches a router advertisement from router
  3. Thus, MN:
    1. configure its IPv6 address (in our case, using the advertised prefix and its own MAC address): this address is the Care of Address (CoA)
    2. memorize the router address, sampled from the router advertisement
  4. MN sends a Binding Update to its Home Agent (using its CoA as sender address)
  5. Home Agent (HA) receives the Binding Update, and answer the MN by a Binding Acknowledgement
  6. HA and MN establish a tunnel between eachother.

When a device wants to talk with the MN, it sends its packets to the Home Network, the HA catch it and resend it through the tunnel. The MN answers directly its correspondant, without using the tunnel nor redirection by the HA : this mecanism is called triangle routing.

The configuration steps are illustrated in this gallery:

The mobile moves to a foreign network
Configuration of MN + exchanges with HA
Tunnel establishment

Here are some screenshots of the frames observed when the MN connects to a visited network:

capture on MN: ask for the router prefix to catch an IP address
Capture on MN: MN sends a BU to its HA
Capture on MN: MN receives BA from its HA ; status is "0", the Binding is accepted by the HA

You can also run a virtual terminal, either on MN and HA; to do so:

   telnet localhost 7777

Thus, you can see the Binding Update Liste on HA, and the Binding List on MN:

On HA:

   mip6d> bc
   hoa 5f02:0:0:0:221:70ff:feb4:ae95 status registered
    coa 5f01:0:0:0:221:70ff:feb4:ae95 flags AH--
    local 5f02:0:0:0:0:0:0:1
    lifetime 22 / 60 seq 32629 unreach 0 mpa - / 6940 retry 0

On MN:

   mip6d>mip6d> bul
   == BUL_ENTRY ==
   Home address    5f02:0:0:0:221:70ff:feb4:ae95
   Care-of address 5f01:0:0:0:221:70ff:feb4:ae95
   CN address      5f02:0:0:0:0:0:0:1
    lifetime = 60,  delay = 57000
    flags: IP6_MH_BU_HOME IP6_MH_BU_ACK 
    ack ready
    lifetime 56 / 60 seq 32631 resend 0 delay 57(after 53s)
    mps 2332735 / 2332798

Other configurations

It is possible to configure MN and HA, in order that MN advertise its Care of Address to the nodes it talks to. This also requires the correspondant to support mobile IPv6, and to be configured as "CN" (Client Node). Otherwise, the communication will happen as previously (triangle routing).

Thus, when a communication between MN and a CN is established, the HA is not used anymore. This spares a lot of time, especially when the MN is far from it's HA and close to the CN.

Unfortunately, we did not had time to test this enhancement. You have to edit the mip6d-xx.conf files to do so.