Subject: RE: Advertise when no addresses available (was: Re: A few additional items re: -19 draft)

From: "Thirumalesh Bhat" <[email-masked]>
Date: Fri, 27 Jul 2001 08:59:47 -0700

The server can remain silent if it doesn't have any addresses to offer.
I don't see much upside for the client if the server says it doesn't
have any addresses to offer.

thx

-----Original Message-----
From: Bernie Volz (EUD) [mailto:[email-masked]] 
Sent: Friday, July 27, 2001 7:48 AM
To: DHCPv6 discussion list
Subject: RE: Advertise when no addresses available (was: Re: A few
additional items re: -19 draft)

Jitesh/Ralph: 

After thinking a bit more about this, there is merit in having the
server respond. 
This at least indicates to the client that the server does exist. And,
it may be 
that the server can provide some useful information to the client even
though it 
is unable to give it addresses. It may well be that some addresses are
stateless 
and these may be of sufficient scope to allow the client to obtain other
useful 
configuration information from the server even if it can not get
addresses. 

So, I agree with Jitesh that the best response is IA w/Unavail error. My
reason for 
this is: 
- I want the server to respond (see above). 
- Responding without the IA likely means to the client that the server
is not willing 
to give out addresses (but is willing to give other configuration
parameters). 

I do not agree with Jitesh that this will flood the network - clients
are supposed 
to retransmit Solicits periodically and will do so if no server exists
anyway. The 
retransmit timers are set to keep this traffic reasonable. Sure, if you
had thousands 
of clients, you could get a fair amount of traffic. But that's not
likely on most 
link technology in use today (to have that many clients). And, if it is
a problem, 
we better readjust the Solicit retransmit timers anyway. 

I do believe we need to spell out the server behavior clearly. So, I
would suggest 
text as follows: 

When responding to a Solicit, the server MUST handle client IA options
as follows: 
- If the server is not configured to offer any addresses to the client
(or link), 
it MUST not include the client's IA option(s) in the Advertise. 
- If the server is configured to offer addresses to the client (or link)
but has 
no addresses to advertise at the moment, it MUST include the client's IA
option(s) 
with an error of "Unavail". 
- If the server is configured to offer addresses and has addresses to
offer, it 
MUST include the client's IA option(s) filled out with address
information [either 
the prefixes or the full addresses, as is TBD]. 

If the above is done, a client can determine whether a server is capable
of offering 
it addresses or not, and whether addresses are presently available or
not. In this 
way, it can determine which server to use (if it needs addresses, use
the highest 
preference server that has addresses available, if none, use the server
that can 
offer addresses but has none at the moment, ...). 

- Bernie 

-----Original Message----- 
From: Jitesh N Verma [mailto:[email-masked]] 
Sent: Friday, July 27, 2001 9:45 AM 
To: DHCPv6 discussion list 
Subject: Re: Advertise when no addresses available (was: Re: A few 
additional items re: -19 draft) 

Ralph, 
        If the server does not respond, client will keep sending Solicit

message, flooding the network. This is particularly true when there is
only 
one server in the network. (If there are multiple server in the network,
other 
servers may respond. No problem in this case). Please keep in mind that
lease 
times are not going to be just few seconds. What I mean to say is that
if the 
IP addresses are not available currently, it may not be available for
quite 
some time. 
        Looking at the various options, I will opt for server responding
with 
IA containing Unavail error. I am not in favour of server responding
with 
num-addrs = 0 , since this sort of IA is used to indicate empty IA. Let
us 
not mix up. Let us provide more clarity to the implementer. 

- Jitesh 

> I vote for the server to not respond if it has no addresses available.

> 
> - Ralph 
> 
> At 12:10 PM 7/23/2001 -0500, Bernie Volz (EUD) wrote: 
> >- When forming the Advertise in response to a Solicit, there 
> >isn't any clear indication of what to do if no addresses may 
> >be available for the client from that server at that time 
> >(because all available addresses are in use). In particular, 
> >should the server: 
> >- Ignore the Solicit (in the hopes that by the time a subsequent 
> >   Solicit arrives, addresses may be available) 
> >- Send the Advertise but without the IA option 
> >- Send the Advertise with the IA option but with an error (such 
> >   as Unavail) 
> >- Send the Advertise with the IA option with num-addrs = 0 
> > 
> >Or, should a client be prepared to handle all of the above? 
> 
> 

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