Subject: [dhcwg] Simplification of DNAv4 specification

From: "Bernard Aboba" <[email-masked]>
Date: Sun, 25 Sep 2005 13:41:18 -0700

It has been suggested that the DNAv4 specification can be simplified by 
recommending that implementations simultaneously test reachability to one or 
more networks in parallel with attempting to obtain a configuration via 
DHCPv4.   While the current specification allows this, it is optional rather 
than recommended behavior, and so the specification still has to accomodate 
the case where an implementation attempts to obtain configuration serially.

By assuming that the implementation attempts to obtain configuration by 
multiple mechanisms in parallel, it can be guaranteed that DNAv4 will not 
take longer than DHCPv4 to obtain a configuration.  It also simplifies the 
DNAv4 client implementation, since the client can determine the set of 
networks for which it has an operable configuration, and select a subset of 
that for reachability testing without having to consider link layer hints.

For example, if a host has a still-valid DHCP leases on three networks, it 
can do 3 reachability tests in parallel with attempting to obtain a 
configuration via DHCPv4.

The downside of this approach is the extra traffic.  However, this risk can 
probably be mitigated via rate limiting, jittering and exponential backoff.  
  Therefore, it appears to me that the benefits of this approach, in terms 
of a simplified implementation and improved performance and robustness are 
worth the costs.

Before making the sugested edits to the document, I thought I would gauge WG 
reaction first.  A strawman draft is available here:
http://www.drizzle.com/~aboba/DNA/draft-ietf-dhc-dna-ipv4-16.txt

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From: "Barr Hibbs" <[email-masked]>
Date: Fri, 30 Sep 2005 12:27:48 -0700

I basically agree with rewording DNAv4 to permit multiple
parallel efforts to configure the client.  We are rapidly
entering an era when network bandwidth is sufficient to all
but eliminate the concern about extra traffic.

Would it be appropriate to add a guideline such as: "clients
on a 10 or 11 Mbit/s network SHOULD NOT attempt more than
two (2) parallel reachability attempts (DHCPv4 and link
local), clients on a 54 or 100 Mbit/s network SHOULD NOT
attempt more than five (5), and clients operating on
networks above 500 Mbits/s MAY attempt as many as they
wish?"  The idea being to suggest a bit of self-restraint
without mandating an inflexible limit.

--Barr