Antonio Quartulli | 9 Nov 15:39 2012

Re: DHCP servers and Subnets in Wireless Mesh Networks [Mesh Architecture]

On Thu, Nov 08, 2012 at 11:28:35AM -0500, Naman Muley wrote:

>    I was reading on with the BATMAN-adv wikis. I understand the functionality
>    to an extent. Here's my question with respect to the translation table: 
>    I guess the translation table keeps record of the clients connected to a
>    particular node. Now, my question is, doesn't this get exhaustive?
>    Typically looking at my deployment scenario, say a library, or a lecture
>    theater, will have atleast 400 people at a place. (Not going into load
>    balancing on one node! ) will the size of the table not become large? I
>    mean then performing a search operation every time a packet addressing the
>    client comes and sending it, will that not become time consuming? As I
>    understand, in the wired counterpart, switches are supported by CAMs which
>    are fast at search operations but a normal router working on it, won't the
>    load become overwhelming very quickly? 

This is a good point.
For sure batman-adv, which is implemented in-kernel, cannot achieve the same
performance as CAMs. Batman-adv uses its own hash table implementation to
perform this task, trying to speed it up as much as possible.
I think there are some examples out there where they use batman-adv with ~300
clients and they didn't report back any issue related to this. You should also
keep in mind that batman-adv probably will not have to handle Gbps of traffic,
as high-level wired bridges do. If you want to handle that high bandwidth, maybe
the wireless medium is not the best approach at all?

>      This is possible with batman-adv, but also with layer3
>      protocols (like OLSRd or Babel): simply because the clients will become
>      part
>      of the node network segment. However, as already mentioned before my
>      reply, with
>      batman-adv the (mesh-un-aware) clients will have their DHCP packets
>      re-routed in
>      a smart way so to choose the best (from the batman-adv metric point of
>      view)
>      DHCP server. In case of a layer 3 protocol, each node should also run
>      the DHCP
>      server, unless you think to some a bit more complex solutions.
>    Coming back to say an OLSR implementation, I don't really understand well
>    enough how will clients move freely if there are multiple subnets. Moving
>    from one MR supporting one sub-net to another will require an IP handover.

I do not use OLSRd that frequently, but I think that in this case the problem is
not OLSRd related anymore: here you probably need to take into consideration
mobile IP and other stuff like that. I think there was an OLSRd plugin some time
ago which was trying to help in this direction..but I don't know whether is
still exists and if it is actively developed or not.



Antonio Quartulli

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