[B.A.T.M.A.N.] Question about multiple GW scenario

[B.A.T.M.A.N.] Question about multiple GW scenario

[Antonio Quartulli]

Hi guys,
I'm writing a short report about the actual behaviour of b.a.t.m.a.n. in
case of client roaming between bat-nodes.

I was wondering what could happen in a particular (but not so unusual)
situation:

take a network made up of several nodes, and 2 IP gateways, say  X and Y.
These 2 gws are advertising themself as gw (via the gw-mode). 
Now we have two nodes A and B which respectively recognize as gw X and Y
(A recognizes X and B recognizes Y, where recognize means "to have such gw
as best gw"). Each gw runs a dhcp server which assigns itsself as default
ip route.

Now, what would it happen if a client roams from A to B and sends a new
dhcp request (cause the lease time has expired) so changing the default
gw from X to Y? The established connections will stop to work.

I think that this is a classical level 3 issue in the hand-off
procedure.
What do you think about this problem? Am I missing something?

Thank you all :)


-- 
Antonio Quartulli

..each of us alone is worth nothing..
Ernesto "Che" Guevara

Re: [B.A.T.M.A.N.] Question about multiple GW scenario

[Marek Lindner]

On Friday 20 August 2010 14:22:52 Antonio Quartulli wrote:
> Now, what would it happen if a client roams from A to B and sends a new
> dhcp request (cause the lease time has expired) so changing the default
> gw from X to Y? The established connections will stop to work.
> 
> I think that this is a classical level 3 issue in the hand-off
> procedure.

This is not entirely correct. When the lease expires the client will try to 
renew its lease. If it still can reach its original gateway it should not 
switch.

However, this might not be desired. The connection towards the old gateway 
might just be good enough to let the DHCP request through but is horrible when 
used for real data. In that case it would be smarter if batman dropped the 
renewal attempt to make sure the client switches.

We have to find the right balance between breaking the established connections 
and having a usable connection.

Cheers,
Marek