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Comments on draft-bagnulo-shim6-addr-selection-00.txt

Hi Marcelo,

And thanks for writing this draft. This is an important
scenario to cover. Generally speaking I like your
solutions. A few comments, however:


5.1.1.  Direct link failures


The title seems a bit misleading. I thought first that
you were talking about the direct link from the host,
but this was really the link from the local router to the
ISP.

Anyway, I think you are missing a discussion of the
first case. Here it may even be that existing mechanisms
already solve the problem, because presumably RFC 3484
would not select source addresses from a link that's down.
But it would still be important to note this.


  The missing part is a mechanism to convey the information from the
  server to the host.  A possible option is to define a new DHCP option
  to transmit policy table information.

This does not appear to be able to deal with dynamic
outages, or does it? At the very least the lease times
would have to be set low.


  It is also possible to enable the multihomed host to query the server
  to obtain the source address prefix information as proposed in [6] .
  In this case, each time the multihomed node initiates a communication
  with a new destiantion, it would query the server for the proper
  prefix to include in the source address.  The server, would reply
  based on the routing information it has gathered through BGP.

This might be a better alternative, perhaps modified by
only doing the query if you can't establish a connection.


  The first option is to simply let the upper layers to handle
  retrials.  In this case, the IP layer only has to make sure that a
  different source address is used in each retrial as long as there is
  not a preferred source address in the source address cache.  So, in
  this approach, when the IP layer receives a packet, it searches the
  Source Address Cache for a preferred source address associated to the
  selected destination.  If no entry exists for that destination
  address, one of the available source addresses is selected randomly.
  If reply packets arrive, an entry will be created in the Source
  Address Cache for that destination address.  If no reply packets
  arrive, no entry will be created, so when the upper layer protocol
  resends the packet, a new source address will be used.

I may be confused here, but I suppose you are not talking
about IP packets, you are talking about connection initiation.
You can't change source address on the fly from an existing
TCP sessions.

--Jari