Subject: [manet] Lunar question

From: DANIEL BYRNE <[email-masked]>
Date: Wed, 31 Mar 2004 08:17:55 -0600

In LUNAR what happens when the xrp layer receives a frame from tcp/ip stack
and it is a data frame with a specific dest. MAC address but we've already
purged the table entry for that MAC address?  Is an automatic XRP RREQ sent
to determine what the MAC address is for the given IP address?  Or, is some
sort of message sent back up the TCP/IP stack telling it that this MAC is
invalid so it knows to create an ARP request to get the MAC address for the
destination?  To me, it seems like we would do that second of the two
choices.  This keeps the upper layers doing what they are suppose to do and
keeps us from having to be too smart, ya know.  So with that said, does
anyone know what the special message is that we send back to the TCP/IP
stack telling it a MAC doesn't exist, or the packet be trashed and let the
TCP/IP logic timeout and create an ARP request on its own?

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From: Christian Tschudin <[email-masked]>
Date: Thu, 1 Apr 2004 00:08:53 +0200 (MET DST)

Daniel, we are in the process of setting up a LUNAR distribution
list where such question will best be handled. I will soon annouce
it and will also come back to your previous questions there.

Regarding your question below:

The answer depends on how closely your LUNAR implementation can
touch the IP stack:

- When a MAC-to-LUNARpath entry expires, you should also invalidate
  the IP stack's ARP cache (simple remove the ARP entry, so a next
  data packet will trigger a new ARP request).

- in case the LUNAR implementation can only use ARP replies to
  talk to the IP stack, you are out of luck: There is no ARP
  message for "undoing" an IP-to-MAC mapping, for obvious security
  reasons.

  The best thing then is to set the ARP timer of the IP stack to low
  values, 3 to 6 seconds instead of the usual 60 seconds.

  Note that although the IP stack now emits frequent ARP requests,
  this is no extra burden for the ether because the LUNAR implementation
  traps all ARP messages and can return IP-to-MAC mappings based on
  its table.

christian.

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Christian Tschudin, University of Basel       http://cn.cs.unibas.ch/
Computer Science Dept, Bernoullistr. 16, CH - 4056 Basel, Switzerland