[support] Binding Update problem

[Romain KUNTZ]

Hi,

On 2008/09/29, at 13:53, Eriza Hafid Fazli wrote:
> The MR has three Ethernet interfaces, eth1, eth2, and eth3. eth1 and  
> eth2
> are used for connection using access routers, AR1 and AR2  
> respectively,
> whereas eth3 is used in the mobile network. The MR moves from AR1 to  
> AR2,
> with the handover triggered by stopping router advertisement (radvd)  
> from
> AR1, and starting one in AR2.

I think stopping radvd is not the best way to force a handover.  
According to the lifetime set in the radvd configuration on AR1, the  
MR may keep the routes in its routing table.

The best way to perform a handover would be to disconnect the MR  
interface, which will trigger a "link down" event and cleanup all the  
routes towards this interface.

> We collected the traffic trace at AR1 and AR2, and discovered that the
> Binding Update (BU) is sent through AR1, whereas the Binding  
> Acknowledgment
> (BA) comes from AR2. We made additional tests by turning down the  
> Ethernet
> interface of AR1 in addition to stopping radvd. In this case the BU  
> never
> arrived at the HA and no handover took place.
>
> We thought that this behaviour may happen because the MR keeps  
> adding a new
> default router entry in its routing table, every time it receives a  
> new
> router advertisement.

I guess the MR still has the old default router in its routing table,  
because it does not know that the router is down as long as the  
lifetime of the entry did not reach 0.

> Is this the intended behaviour of the code? We had an expectation  
> that the
> BU should have been sent using AR2, since for instance in the case  
> that the
> handover is triggered due to AR1 failure, all communication from/to  
> the MR
> will be completely cut as no handover will ever take place.

I think the the handover will properly occur once the MR cleanups its  
old route entries: for that purpose you could put a smaller lifetime  
in your RA, and send RA more regularly on AR1.

Regards,
-- 
Romain KUNTZ
kuntz at lsiit.u-strasbg.fr
LSIIT - Networks and Protocols Team
http://clarinet.u-strasbg.fr/~kuntz/