Network association algorithm

Michail Bletsas mbletsas at
Wed May 9 14:45:41 EDT 2007


I think that your approach fits perfectly with our latest connection 
flowchart and I would like to see it implemented asap.


"Javier Cardona" <javier at> 
05/04/2007 02:39 PM

"John Watlington" <wad at>
"Dan Williams" <dcbw at>, "Michail Bletsas" <mbletsas at>, 
"OLPC Devel" <devel at>
Re: Network association algorithm

Hi John, Dan,

After chatting with Dan I finally understood your flowchart (pardon my
thickness,  I was having some nomenclature problems..).  I learned 

 1) "established MPPs" are MPPs with multiple mesh interfaces, at most one 
 each channel 1,6 and 11.  They are also called "school servers" and will 
 be moving around.

 2) "ad-hoc MPPs" are xo's that act as MPPs, as portals they were
originally conceived.

 3) Addresses are assigned by DHCP because link local addresses cannot be
 routed.  L3 routing is done by MPPs across mesh segments at different

Based on this understanding, I would like to suggest a change in the way 
is used in your proposal.  The current flow is:

       +           +
      / \         / \
     /   \ y     /   \ y
----+DHCP?+-----+ MPP?+----
     \   /       \   /
      \ /         \ /
       + n         + n
       |           |

This approach separates IP address assignment (DHCP) and MPP detection and 
selection.  I believe these two functions which can be combined in one:

1. xo sends a DCHP request to L2 address ANY_MPP.  This is a standard
DHCPREQUEST sent to a unicast address.  The only thing "non-standard" 
would be
done at the dhcp client:  this DHCPREQUEST would have the L2 anycast
address, the L3 broadcast address and would be injected at L2 using
the linux packet interface.

2. MPP assigns an IP address and sends a DHCPACK to the L2 address that 
was in
the DHCPREQUEST.  That's vanilla DHCP server.

3. The xo knows the DHCPACK comes from an MPP because it's a response from 
request sent to the ANY_MPP address.


1. Faster configuration.
2. No broadcast+anycast traffic, only anycast.
3. Replaces non-standard MPPREQs with standard DHCP

This model can also be used for ad-hoc MPPs.  In that case ad-hoc MPPs 
return gateway and DNS information but would not assign an IP address.

What do you think?


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