[Olsr-users] AHCP

[Henning Rogge]

Am Thursday 26 February 2009 22:53:48 schrieb Robert Keyes:
> Well, it's certainly easy enough to use the MAC address to generate IP
> addresses and it will _probably_ work just fine. But it's not robust.
> Beyond that, there are certain problems with which highest-order octet to
> use. I am pretty sure that there is no one who has a spare 'class A' (a
> /8, in CIDR notation) in publicly-routed IP space which is completely
> spare and can be used for a mesh network. That leaves the possibilities of
> either using 'private ip space', as specified in RFC 1918, or breaking
> routing rules and potentially causing a problem by taking a class A and
> using it as private IP space. The only RFC compliant space is 10.0.0.0/8.
> The problem is, this is used by other people in their own internal
> network, behind their NAT. This is why MIT chose to break the routing
> rules and use 5.0.0.0/8 and 6.0.0.0/8 for RoofNet. The problem is these IP
> blocks are owned by Symbolics and Honeywell-Bull, respectively, and if
> these companies ever decide to announce a route to these network
> addresses, or (more likely) the numbers become reassigned to other
> entities who route them, then trouble will arise. But hey? Why think about
> tomorrow or next year or next decade...it works now!
IPv6... if we run out of address space there, we will think about the problem 
again.

> I would expect that after 2011, when we are projected to 'run out' of IPv4
> space, that there will be much reassignment, and reclaiming of large
> blocks of unrouted IP space such as 5 and 6 mentioned above and many
> others. But if you're okay with having to renumber down the road, then go
> ahead and use them.
>
> But say that you want to be able to provide users of your mesh network
> with 'real' publicly routed IP addresses, and not an address behind a NAT.
> There's a bunch of protocols and applications that work better when they
> have a 'real' IP address. I can do this, because I have a class C -
> 205.159.169.0/24. If I were to renumber the MAC addresses of the devices
> on my mesh, using an unassigned vendor prefix, I could then assign the
> least significant octet from 1-254 as needed, and align with the IP
> addresses, and thus avoid the use of ARP or hosts tables which is the
> reason for this whole MAC to IP mapping in the first place. Of course, I
> wonder if it wouldn't be more reasonable to continue to use ARP, but set
> the TTL to a high number, such as an hour, to keep the amount of ARP
> traffic on the mesh to a minimum, yet still have the flexibility that ARP
> provides. We could even use DHCP. It could be easy. Maybe ARP needs to
> come back.
We will just switch to IPv6 for OLSR networks. It's not that difficult to 
route IPv4 traffic through IPv6 mesh clouds.

> What about 802.11s? How is arp going to work with that?
802.11s runs on layer 2 with MAC addresses, it does not even know about IP I 
think.

Henning

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