[e2e] TCP Option Negotiation

Ralph Droms rdroms at cisco.com
Thu May 17 09:53:50 PDT 2001

I've had discussions about enforcing a quiet time in DHCP - a minimum delay 
time before reassigning an address to a new host.

We've never heard a sufficiently strong argument to warrant adding the 
requirement to the DHCP spec.  I don't know of any servers that implement a 
quiet time.

- Ralph

At 12:25 PM 5/17/2001 -0400, John Wroclawski wrote:
>At 11:57 AM -0400 5/17/01, Hari Balakrishnan wrote:
>>>  Alex,
>>>  This seems to be another manifestation of the standard  problem of old
>>>  duplicate packet.   Your scenario is a violation of TCP's "quiet time"
>>>  requirement upon host crash and restart (it's the same host if it has
>>>  the same IP address).  Quiet time is a vital part of TCP's machinery to
>>>  protect against old duplicates.
>>Not quite.
>>Unfortunately the statement: "it's the same host if it has the same IP 
>>is increasingly untrue because of dynamic IP address assignment (e.g., via
>>DHCP).  This may well be a theoretical problem, but I've observed (in my 
>>from my FreeBSD DHCP server), turning off a laptop and turning another 
>>one on,
>>and having the latter receive the former's IP!
>It might be arguable that RFC793 actually covers this. Crash/restart is 
>used as the motivating example, but the words are more general - "in the 
>absence of knowledge about the sequence numbers used on a particular 
>connection, the TCP specification recommends that the source delay for MSL 
>seconds before emitting segments on that connection, to allow time for 
>segments from an earlier connection incarnation to drain from the system".
>An implementation that truly followed this recommendation would enforce a 
>quiet time after any assignment of a dynamic address on the grounds that 
>it had no idea where that address had been before, and thus no knowledge 
>about previous SN's..

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