[B.A.T.M.A.N.] how to make IP layer handle the change of network topology

[B.A.T.M.A.N.] how to make IP layer handle the change of network topology

[liudows]

Hello, eveyone, I am learning the batman.adv recently.   

We know that batman.adv works on layer 2. When the network topology change, batman.adv can know this change and handle it. But the IP layer doesn't know that. How to make IP layer handle the change of network topology?  

For example, I have 3 mesh nodes, client node A, gateway node B and geteway node C. A connects  to internet via B. Then I shutdown B. I guess A will switch to C as it's gateway node automatically. But it's not so. A continuously send the ARP request packet to search the MAC address of B. The default gateway is still B, not C.  

So, how should I do to make the IP layer be aware of that the gateway has swithed to another one?  

Thanks! Best regards.  

liu  

Re: [B.A.T.M.A.N.] how to make IP layer handle the change of network topology

[Antonio Quartulli]

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Hi Lui,

there is no direct way to get a topology change in userspace unless you
want to parse the originator table (and even in that case you will only
see "local" changes).

The behaviour you described about the ARP packets is normal because the
IP layer does not know anything about changes happening at the
batman-adv layer. You need to handle them by yourself (if possible).

However it looks like you want to detect a "gateway change" rather than
a real "topology change".

Please check this link[1] out that is explaining how batman-adv tells
userspace about GW changes.

Cheers,


[1] http://www.open-mesh.org/projects/batman-adv/wiki/Uevent#Gateway-uevents

On 07/08/14 09:49, liudows wrote:
> Hello, eveyone, I am learning the batman.adv recently.   
> 
> We know that batman.adv works on layer 2. When the network topology change, batman.adv can know this change and handle it. But the IP layer doesn't know that. How to make IP layer handle the change of network topology?  
> 
> For example, I have 3 mesh nodes, client node A, gateway node B and geteway node C. A connects  to internet via B. Then I shutdown B. I guess A will switch to C as it's gateway node automatically. But it's not so. A continuously send the ARP request packet to search the MAC address of B. The default gateway is still B, not C.  
> 
> So, how should I do to make the IP layer be aware of that the gateway has swithed to another one?  
> 
> Thanks! Best regards.  
> 
> liu  
> 

-- 
Antonio Quartulli


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Re: [B.A.T.M.A.N.] how to make IP layer handle the change of network topology

[Simon Wunderlich]

Hi liu,

> Hello, eveyone, I am learning the batman.adv recently.
> 
> We know that batman.adv works on layer 2. When the network topology change,
> batman.adv can know this change and handle it. But the IP layer doesn't
> know that. How to make IP layer handle the change of network topology?

The IP layer does not need to know - to the upper layers, a batman-adv network 
appears to be a network where all nodes are just one hop away - although they 
might be more far away in practice. So if you insert an IP packet, it will get 
transported automatically to the right destination (provided batman-adv knows 
where that is), even over multiple hops. 

> 
> For example, I have 3 mesh nodes, client node A, gateway node B and geteway
> node C. A connects  to internet via B. Then I shutdown B. I guess A will
> switch to C as it's gateway node automatically. But it's not so. A
> continuously send the ARP request packet to search the MAC address of B.
> The default gateway is still B, not C.

This will only work if the gateways IP stays the same. This could work like 
that:
 * connect B and C to the same LAN, and enable bridge loop avoidance in 
batman-adv
 * This LAN should have only one router to the internet (e.g. your ADSL 
modem).
 * bridge the batman-interface bat0 and you Ethernet interface eth0 using a 
linux bridge device



> 
> So, how should I do to make the IP layer be aware of that the gateway has
> swithed to another one?
> 
> Thanks! Best regards.
> 
> liu
---
Mit freundlichen Grüßen / kind regards
Simon Wunderlich

Fon: +49 (0) 3741 / 2518068-0
Fax: +49 (0) 3741 / 2518068-9

Re: [B.A.T.M.A.N.] how to make IP layer handle the change of network topology

[Simon Wunderlich]

Bah, i hit the wrong button before finishing the mail :)

> Hi liu,
> 
> > Hello, eveyone, I am learning the batman.adv recently.
> > 
> > We know that batman.adv works on layer 2. When the network topology
> > change, batman.adv can know this change and handle it. But the IP layer
> > doesn't know that. How to make IP layer handle the change of network
> > topology?
> 
> The IP layer does not need to know - to the upper layers, a batman-adv
> network appears to be a network where all nodes are just one hop away -
> although they might be more far away in practice. So if you insert an IP
> packet, it will get transported automatically to the right destination
> (provided batman-adv knows where that is), even over multiple hops.
> 
> > For example, I have 3 mesh nodes, client node A, gateway node B and
> > geteway node C. A connects  to internet via B. Then I shutdown B. I
> > guess A will switch to C as it's gateway node automatically. But it's
> > not so. A continuously send the ARP request packet to search the MAC
> > address of B. The default gateway is still B, not C.
> 
> This will only work if the gateways IP stays the same. This could work like
> that:
>  * connect B and C to the same LAN, and enable bridge loop avoidance in
> batman-adv
>  * This LAN should have only one router to the internet (e.g. your ADSL
> modem).
>  * bridge the batman-interface bat0 and you Ethernet interface eth0 using a
> linux bridge device

Please see our quick start guide for more information on the topic:

http://www.open-mesh.org/projects/batman-adv/wiki/Quick-start-guide#Mixing-
non-BATMAN-systems-with-batman-adv

> 
> > So, how should I do to make the IP layer be aware of that the gateway has
> > swithed to another one?

By using bridges, you always send to the same gateway in your LAN, which does 
not change IP or MAC addresses - so your clients don't need to be aware of the 
topology change.

Cheers,
     Simon

Re: [B.A.T.M.A.N.] how to make IP layer handle the change of network topology

[Antonio Quartulli]

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On 07/08/14 10:24, Antonio Quartulli wrote:
> Hi Lui,

Sorry I misspelled your name. I meant Liu :)

Cheers,


-- 
Antonio Quartulli


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Re: [B.A.T.M.A.N.] how to make IP layer handle the change of network topology

[liu]

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Thanks for reply. I have tried to fix this problem followed by Simon's 
guide.  Unfortunately It stil doesn't work.I draw a pciture named 
'topo.jpg' in the  attachment to describe my situation.

Gateway B and C are wired to router 192.168.1.1 through their 'WAN' 
interface. They are in the same LAN. 'bat0' and 'eth0' are bridged by 
'br-lan' interface, and are assigned a mesh subnet IP address '10.130.1.x'.

Client A connected to B and C by mesh network. 'bat0' and 'wan' is 
bridged by 'br-wan' in Client A. 'br-wan' is assigned a subnet IP 
address by DHCP server in B or C, for example '10.130.1.138'.

Now,  client A choose B as it's gateway, and it's routing table is :
root@dragino2-71e100:~# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref Use   
Iface
default         10.130.1.20     0.0.0.0         UG       0 0 0     br-wan
10.10.1.0        *              255.255.255.0   U        0 0 0     wlan0-1
10.130.1.0       *              255.255.255.0   U        0 0 0     br-lan
10.130.1.0       *              255.255.255.0   U        0 0 0     br-wan

Now, I can ping to the  router ' 192.168.1.1'  from A.

Then, shuting down the node B. In the routing table of A,  node B is 
still the default gateway. A can't ping to '192.168.1.1' now.

The key of this issue is client A and the internet router are not in the 
same network segment. So, the default gateway of A is B or C, but not 
the router. If B is lost, A can't change it's default gateway to C. In 
another words, it's not a self-healing network in this situation.


Best regards,
liu



在 2014/8/7 16:32, Simon Wunderlich 写道:
> Bah, i hit the wrong button before finishing the mail :)
>
>> Hi liu,
>>
>>> Hello, eveyone, I am learning the batman.adv recently.
>>>
>>> We know that batman.adv works on layer 2. When the network topology
>>> change, batman.adv can know this change and handle it. But the IP layer
>>> doesn't know that. How to make IP layer handle the change of network
>>> topology?
>> The IP layer does not need to know - to the upper layers, a batman-adv
>> network appears to be a network where all nodes are just one hop away -
>> although they might be more far away in practice. So if you insert an IP
>> packet, it will get transported automatically to the right destination
>> (provided batman-adv knows where that is), even over multiple hops.
>>
>>> For example, I have 3 mesh nodes, client node A, gateway node B and
>>> geteway node C. A connects  to internet via B. Then I shutdown B. I
>>> guess A will switch to C as it's gateway node automatically. But it's
>>> not so. A continuously send the ARP request packet to search the MAC
>>> address of B. The default gateway is still B, not C.
>> This will only work if the gateways IP stays the same. This could work like
>> that:
>>   * connect B and C to the same LAN, and enable bridge loop avoidance in
>> batman-adv
>>   * This LAN should have only one router to the internet (e.g. your ADSL
>> modem).
>>   * bridge the batman-interface bat0 and you Ethernet interface eth0 using a
>> linux bridge device
> Please see our quick start guide for more information on the topic:
>
> http://www.open-mesh.org/projects/batman-adv/wiki/Quick-start-guide#Mixing-
> non-BATMAN-systems-with-batman-adv
>
>>> So, how should I do to make the IP layer be aware of that the gateway has
>>> swithed to another one?
> By using bridges, you always send to the same gateway in your LAN, which does
> not change IP or MAC addresses - so your clients don't need to be aware of the
> topology change.
>
> Cheers,
>       Simon
>


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Re: [B.A.T.M.A.N.] how to make IP layer handle the change of network topology

[Simon Wunderlich]

Hello Liu,

> Thanks for reply. I have tried to fix this problem followed by Simon's
> guide.  Unfortunately It stil doesn't work.I draw a pciture named
> 'topo.jpg' in the  attachment to describe my situation.
> 
> Gateway B and C are wired to router 192.168.1.1 through their 'WAN'
> interface. They are in the same LAN. 'bat0' and 'eth0' are bridged by
> 'br-lan' interface, and are assigned a mesh subnet IP address '10.130.1.x'.
> 
> Client A connected to B and C by mesh network. 'bat0' and 'wan' is
> bridged by 'br-wan' in Client A. 'br-wan' is assigned a subnet IP
> address by DHCP server in B or C, for example '10.130.1.138'.

You are still doing routing in that scenario. Instead, you should bridge all 
nodes in the same network, and they should be in the same IP subnet. If you 
configure another WAN, you are back to routing, which will not work for that 
scenario.

Please configure eth0, wan and bat0 in the same bridge (e.g. br-lan) on all 
devices. Don't configure other bridges. Then, your devices and your client 
should get an IP address from the 192.168.1.x subnet, and should be able to 
ping 192.168.1.1, even if node A fails.

Cheers,
     Simon