[B.A.T.M.A.N.] Multiple DHCP Gateways

[B.A.T.M.A.N.] Multiple DHCP Gateways

[gtolon]

Hi

I´m testing the Gateway roaming capabilities of Batman-adv (using 
2011.1.0 version). I setted two computers as Gateway servers with DHCP 
servers running on them and other as Gateway client, configured as class 
3. Then i stressed individually the Gateway server´s links to make the 
client choose the not stressed one. I confirmed that when te client 
sends a layer 3 broadcast DHCP request, Batman redirects that request 
only to the best gateway. However, when the original gateway becomes 
worse than the alternative, and the client chooses the new one as 
preferred (observed with batctl gwl) i noticed that the subsequent 
request DHCP messages are sent to the original server, even if it 
doesn´t have the best link.

I guess that´s because these subsequent DHCP requests are made as 
Unicast to the original server and so Batman doesn´t redirect them, but 
i wonder how this behavior affects the network balance, because the 
computers would get tied always to the original DHCP and IP default 
gateway even if they moved, right?

Thank you very much

Re: [B.A.T.M.A.N.] Multiple DHCP Gateways

[Antonio Quartulli]

Hello and thank you for sharing your gw experience with us,

On Wed, Aug 10, 2011 at 02:52:06PM -0300, gtolon@inti.gob.ar wrote:
> Hi
[CUT]
> However, when the original gateway becomes 
> worse than the alternative, and the client chooses the new one as 
> preferred (observed with batctl gwl) i noticed that the subsequent 
> request DHCP messages are sent to the original server, even if it 
> doesn´t have the best link.
> 
> I guess that´s because these subsequent DHCP requests are made as 
> Unicast to the original server and so Batman doesn´t redirect them, 

Unicast renewal requests are "dropped" only if the TQ towards the destination is
smaller than the "current_GW_TQ - GW_THRESHOLD" (GW_THRESHOLD = 50).
To clarify:


In your topology you have three nodes: A, B and C. A and C are GWs. A is the
current best GW for B and B got an IP from the DHCP server running on A. Then
the link A <--> B becomes worse than B <--> C. At this point Batman-adv will
drop a DHCP unicast renewal request directed to A 

if and only if TQ(C) - TQ(A) > 50

Is this condition verified in your topology when your are observing the renewal
DHCP packets?

I hope I've been clear. :-)

> but 
> i wonder how this behavior affects the network balance, because the 
> computers would get tied always to the original DHCP and IP default 
> gateway even if they moved, right?

As above. Clients will keep the same GW as long as the link is still "usable"
(difference on TQs greater than 50)

> 
> Thank you very much

Thank you too,
Antonio

Re: [B.A.T.M.A.N.] Multiple DHCP Gateways

[Marek Lindner]

On Friday, August 12, 2011 18:02:20 Antonio Quartulli wrote:
> In your topology you have three nodes: A, B and C. A and C are GWs. A is
> the current best GW for B and B got an IP from the DHCP server running on
> A. Then the link A <--> B becomes worse than B <--> C. At this point
> Batman-adv will drop a DHCP unicast renewal request directed to A
> 
> if and only if TQ(C) - TQ(A) > 50

Be aware that only happens if you use the git repository. The "DHCP request 
drop" feature was not released yet.

What version are you using ?

Cheers,
Marek

Re: [B.A.T.M.A.N.] Multiple DHCP Gateways

[P. Mazart]

Hi,

> I´m testing the Gateway roaming capabilities […]
> […], even if it doesn´t […]
> […] I guess that´s because these subsequent DHCP requests […]

Please don’t use the accute as an apostrophe.
You could use “ ' ” (U+0027/ASCII) or even better
a typografically true “ ’ ” (U+2019)…

Best Regards,
P.M.

Re: [B.A.T.M.A.N.] Multiple DHCP Gateways

[gtolon]

Thank you for your answers. I understood clearly how the system should 
work, but i´m not using the git repository but the 2011.1.0 version. 
I'll try with the repo to see what happens.

Best regards

Gabriel




> Message: 2
> Date: Fri, 12 Aug 2011 18:02:20 +0200
> From: Antonio Quartulli<ordex@autistici.org>
> To: The list for a Better Approach To Mobile Ad-hoc Networking
> 	<b.a.t.m.a.n@lists.open-mesh.org>
> Subject: Re: [B.A.T.M.A.N.] Multiple DHCP Gateways
> Message-ID:<20110812160217.GB22361@ritirata.org.org>
> Content-Type: text/plain; charset=utf-8
>
> Hello and thank you for sharing your gw experience with us,
>
> On Wed, Aug 10, 2011 at 02:52:06PM -0300, gtolon@inti.gob.ar wrote:
>> Hi
> [CUT]
>> However, when the original gateway becomes
>> worse than the alternative, and the client chooses the new one as
>> preferred (observed with batctl gwl) i noticed that the subsequent
>> request DHCP messages are sent to the original server, even if it
>> doesn?t have the best link.
>>
>> I guess that?s because these subsequent DHCP requests are made as
>> Unicast to the original server and so Batman doesn?t redirect them,
>
> Unicast renewal requests are "dropped" only if the TQ towards the destination is
> smaller than the "current_GW_TQ - GW_THRESHOLD" (GW_THRESHOLD = 50).
> To clarify:
>
>
> In your topology you have three nodes: A, B and C. A and C are GWs. A is the
> current best GW for B and B got an IP from the DHCP server running on A. Then
> the link A<-->  B becomes worse than B<-->  C. At this point Batman-adv will
> drop a DHCP unicast renewal request directed to A
>
> if and only if TQ(C) - TQ(A)>  50
>
> Is this condition verified in your topology when your are observing the renewal
> DHCP packets?
>
> I hope I've been clear. :-)
>
>> but
>> i wonder how this behavior affects the network balance, because the
>> computers would get tied always to the original DHCP and IP default
>> gateway even if they moved, right?
>
> As above. Clients will keep the same GW as long as the link is still "usable"
> (difference on TQs greater than 50)
>
>>
>> Thank you very much
>
> Thank you too,
> Antonio
>
>
> ------------------------------
>
> Message: 3
> Date: Fri, 12 Aug 2011 19:22:28 +0200
> From: Marek Lindner<lindner_marek@yahoo.de>
> To: "The list for a Better Approach To Mobile Ad-hoc Networking"
> 	<b.a.t.m.a.n@lists.open-mesh.org>
> Subject: Re: [B.A.T.M.A.N.] Multiple DHCP Gateways
> Message-ID:<201108121922.28786.lindner_marek@yahoo.de>
> Content-Type: Text/Plain;  charset="utf-8"
>
> On Friday, August 12, 2011 18:02:20 Antonio Quartulli wrote:
>> In your topology you have three nodes: A, B and C. A and C are GWs. A is
>> the current best GW for B and B got an IP from the DHCP server running on
>> A. Then the link A<-->  B becomes worse than B<-->  C. At this point
>> Batman-adv will drop a DHCP unicast renewal request directed to A
>>
>> if and only if TQ(C) - TQ(A)>  50
>
> Be aware that only happens if you use the git repository. The "DHCP request
> drop" feature was not released yet.
>
> What version are you using ?
>
> Cheers,
> Marek
>
>
> ------------------------------
>
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>
>
> End of B.A.T.M.A.N Digest, Vol 56, Issue 15
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Re: [B.A.T.M.A.N.] Multiple DHCP Gateways

[Antonio Quartulli]

On Mon, Aug 15, 2011 at 12:54:47PM -0300, gtolon@inti.gob.ar wrote:
> Thank you for your answers. I understood clearly how the system should 
> work, but i´m not using the git repository but the 2011.1.0 version. 

Ah ok, then everything is ok with your description: successive DHCP requests are
sent in unicast and so to they are sent to the old GW, even if the node serving
the client just chose a new GW.

Please, feel free to share your experience with the git version :-)

Regards,
Antonio