Subject: [manet] AODV previous Hop Address

From: "Saurabh" <[email-masked]>
Date: Mon, 19 Feb 2007 14:14:18 +0530

Hi All,

In RFC 3561 (AODV Routing) Section 6.2 page no. 13 it is mentioned that whenever a node recieves a data packet, it has to update the Active Route time for previous hop.

Referernce:

Each time a route is used to forward a data packet, its Active Route
   Lifetime field of the source, destination and the next hop on the
   path to the destination is updated to be no less than the current
   time plus ACTIVE_ROUTE_TIMEOUT.  Since the route between each
   originator and destination pair is expected to be symmetric, the
   Active Route Lifetime for the previous hop, along the reverse path
   back to the IP source, is also updated to be no less than the current
   time plus ACTIVE_ROUTE_TIMEOUT.  The lifetime for an Active Route is
   updated each time the route is used regardless of whether the
   destination is a single node or a subnet.Kindly tell me how can I get the previous Hop Ip Address? I am unable to find this address.Thanks & Regards,Saurabh Jain

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---

From: Ryan Boder <[email-masked]>
Date: Mon, 19 Feb 2007 10:50:08 -0500

Saurabh wrote:
> Kindly tell me how can I get the previous Hop Ip Address? I am unable to find this address.

In Netwiser we get it from the ARP module if ARP is used. If ARP isn't 
being used we just have a static mapping from IP address to MAC address 
so you can easily figure it out based on the previous hops MAC address, 
which is available from the 802.11 header.

-- 
Ryan Boder
http://bitwiserlabs.com

---

From: "Ian Chakeres" <[email-masked]>
Date: Mon, 19 Feb 2007 11:38:50 -0800

The Previous Hop IP address is the IP Source Address in the packet,
since all messages are only link-local (one hop).

Ian Chakeres

On 2/19/07, Saurabh <[email-masked]> wrote:
>
>
> Hi All,
>
> In RFC 3561 (AODV Routing) Section 6.2 page no. 13 it is mentioned that
> whenever a node recieves a data packet, it has to update the Active Route
> time for previous hop.
>
> Referernce:
>
>  destination is a single node or a subnet.
>
>
> Thanks & Regards,
> Saurabh Jain

---

From: "Saurabh" <[email-masked]>
Date: Tue, 20 Feb 2007 09:09:06 +0530

Hi Ryan,

I think you are refering to some simulator. Can you please tell me how to 
get the same in real time?
----- Original Message ----- 
From: "Ryan Boder" <[email-masked]>
To: "Saurabh" <[email-masked]>
Cc: <[email-masked]>
Sent: Monday, February 19, 2007 9:20 PM
Subject: Re: [manet] AODV previous Hop Address

> being used we just have a static mapping from IP address to MAC address so 
> you can easily figure it out based on the previous hops MAC address, which 
> is available from the 802.11 header.
>
> -- 
> Ryan Boder
> http://bitwiserlabs.com
>
>

---

From: Ryan Boder <[email-masked]>
Date: Mon, 19 Feb 2007 23:35:23 -0500

Hi Saurabh,

Netwiser is framework and IDE that can run your code in a simulator, or 
it can run it in real time on embedded operating systems such as linux. 
So you can get it in real time if you compile your code for linux 
instead of the simulator.

But as Ian pointed out, if all the IP transmissions are 1-hop, you can 
just look at the IP source address. I must have misunderstood the RFC 
because in my AODV code the data packets were multihop at the IP layer. 
Therefore I ran into the same problem as you and solved it using either 
of the two solutions described below.

Sorry if I confused you,
Ryan

Saurabh wrote:
> Hi Ryan,
> 
> I think you are refering to some simulator. Can you please tell me how 
> to get the same in real time?
> ----- Original Message ----- From: "Ryan Boder" <[email-masked]>
>> being used we just have a static mapping from IP address to MAC 
>> address so you can easily figure it out based on the previous hops MAC 
>> address, which is available from the 802.11 header.
>>
>> -- 
>> Ryan Boder
>> http://bitwiserlabs.com
>>
>>
> 

-- 
Ryan Boder
http://bitwiserlabs.com

---

From: "Saurabh" <[email-masked]>
Date: Tue, 20 Feb 2007 10:13:46 +0530

Hi Ryan,

According to my understanding only the control packets of AODV are single 
hop.Data packets can be mutiple hops,in that case i wont be able to get 
previous hop  afddress from IP packet.

Saurabh
----- Original Message ----- 
From: "Ryan Boder" <[email-masked]>
To: "Saurabh" <[email-masked]>
Cc: <[email-masked]>
Sent: Tuesday, February 20, 2007 10:05 AM
Subject: Re: [manet] AODV previous Hop Address

> Hi Saurabh,
>
> Netwiser is framework and IDE that can run your code in a simulator, or it 
> can run it in real time on embedded operating systems such as linux. So 
> you can get it in real time if you compile your code for linux instead of 
> the simulator.
>
> Therefore I ran into the same problem as you and solved it using either of 
> the two solutions described below.
>
> Sorry if I confused you,
> Ryan
>
>
> Saurabh wrote:
>> Hi Ryan,
>>

---

From: Ryan Boder <[email-masked]>
Date: Tue, 20 Feb 2007 15:24:12 -0500

Hi Saurabh,

That was my understanding too. But someone who knows AODV a lot better 
than me said otherwise, so I'll have to concede. All I can tell you are 
some other solutions I've used.

One is to use a static mapping between IP address and MAC address. Most 
802.11 cards let you set the MAC address from software so you could have

IP = 1.1.1.1 <-> MAC = 00:00:01:01:01:01
IP = 1.1.1.2 <-> MAC = 00:00:01:01:01:02

or something like that. Then you can always figure out one address from 
the other.

Another solution, if you are using ARP, is to have ARP keep track of it 
for you. Usually ARP just maps IP addresses to MAC addresses, but maybe 
you can modify your ARP to make it also store reverse mappings, ie MAC 
address to IP address. The ARP implementation in Netwiser does just that 
and it's worked for me. (Also, RARP does the same thing, maybe you could 
figure out a way to use it, I haven't tried)

If you are just using linux or something it might be kind of hard to 
modify ARP like that since it's in the kernel. Then I you might want to 
use the static mapping solution. In Netwiser we have our own ARP module 
in user space that stores reverse mappings to solve that problem. 
Netwiser just grabs packets from the linux ethernet device and bypasses 
the whole linux ARP/IP implementation. Our portable modules that run in 
user space as well as in the simulator do all the work. So the point is, 
by the time an incoming packet reaches the AODV module, it's already 
gone through the ARP module which looked up the reverse mapping and 
stored the previous hop IP address with the packets meta data, so the 
the AODV module just reads it from there.

Ryan

Saurabh wrote:
> Hi Ryan,
> 
> According to my understanding only the control packets of AODV are 
> single hop.Data packets can be mutiple hops,in that case i wont be able 
> to get previous hop  afddress from IP packet.
> 
> Saurabh
>> Netwiser is framework and IDE that can run your code in a simulator, 
>> or it can run it in real time on embedded operating systems such as 
>> linux. So you can get it in real time if you compile your code for 
>> linux instead of the simulator.
>>
>> because in my AODV code the data packets were multihop at the IP 
>> layer. Therefore I ran into the same problem as you and solved it 
>> using either of the two solutions described below.
>>
>> Sorry if I confused you,
>> Ryan
>>
>>
>> Saurabh wrote:
>>> Hi Ryan,
>>>
>>> I think you are refering to some simulator. Can you please tell me 
>>> how to get the same in real time?
>>>> In Netwiser we get it from the ARP module if ARP is used. If ARP 
>>>> isn't being used we just have a static mapping from IP address to 
>>>> MAC address so you can easily figure it out based on the previous 
>>>> hops MAC address, which is available from the 802.11 header.
>>>>
>>>> -- 
>>>> Ryan Boder
>>>> http://bitwiserlabs.com
>>>>
>>>>
>>>
>>
>>
>> -- 
>> Ryan Boder
>> http://bitwiserlabs.com
>>
>>
> 

-- 
Ryan Boder
http://bitwiserlabs.com