RE: [dhcwg] Comments on 22 rev of the draft

"Bernie Volz (EUD)" <> Wed, 16 January 2002 19:26 UTC

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From: "Bernie Volz (EUD)" <>
To: 'Vijay Bhaskar A K' <>,
Subject: RE: [dhcwg] Comments on 22 rev of the draft
Date: Wed, 16 Jan 2002 13:08:33 -0600
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Let me try to answer these based on my understanding/view of -22.

See below.

- Bernie

-----Original Message-----
From: Vijay Bhaskar A K []
Sent: Wednesday, January 16, 2002 1:05 PM
Subject: [dhcwg] Comments on 22 rev of the draft

I had gone through the latest rev of DHCPv6  draft.  Sorry for the delay
in telling the comments.

- I think we need to fix the order of occurence  some  options  that can
appear in the dhcp  messages.  I think,  the DUID  option  should  occur
before the IA option.  This makes the processing simpler.

BV> I think this would be good to say that a client MUST place the DUID option in a mesage before any IA options. 

- I didn't get, why the authentication option should be the last one.  I
feel like it should be the first one.  If the  server/client is not able
to validate the  authentication, it can straight away discard the packet
without further processing.

BV> I too wouldn't mind having this earlier. It makes it easier to validate messages since one doesn't have to process all of the options (or at least parse to some extent all of the options) before one can authenticate the message. But, I would call this a SHOULD not a MUST.

- Section 13 says the ways for selecting  addresses  for  assignment  in
IAs.  Assume, the server has got a direct  message from the client.  The
IP datagram source address is a site-local one.  The message is received
on the server's  interface,  which is configured with a global  address.
According to the draft, the server  should  assume that the client is on
the link  identified  by the  sitelocal  address in  datagram.  Now, the
problem   arises,  if  the  server  is  not  configured  for  allocating
site-local  address for the link.  Now, can the server assume, since the
client has sent the direct message, it is on the same link as the server
and assign it an address of global  scope,  with the same  prefix of its
received  interface.  I think, i have already raised the similar kind of
problem previously, the answer i had got was to select address of global
scope.  Then, the server  should not select the link based on the source
address.  This  is an  implementation  problem  we  faced.  FYI,  HP has
officially  released DHCPv6.  This  implementation  is based on 16th and
some  portion of 18th  version of the  draft.  This  software  is freely
available  at  You can  download it and tell me
your comments.

BV> Section 13 tells how to determine the *LINK* the client is on. Once
that has been done, you assign addresses based on the prefixes that the
server has configured for that *LINK*. If the source address for the
DHCP message was a link local, the server knows that it can't have come
from anywhere but that link (since link-local are only valid locally).
But this only determines the LINK for the client; not the addresses.

- Using DUID, how the address selection is done?

BV> I don't understand what you are asking here. 

- The draft  says that, when the client  needs an  additional  temporary
address, it can include OPTION_RTA encapsulated in OPTION_IA and get the
additional one.  This means, in the same IA, any number of addresses can
be can be added and deleted.  Will it hold for normal addresses also?  I
mean, for  additional  normal  addresses,  whether the client has to use
already  existing IA to get additional  address (or) will it use a fresh
IA?  I remember that, the answer i got for this question 3-4 months back
was that the client will use fresh IA,  because,  adding  address to the
same IA will lead  complexity.  Just in curiosity, i am asking, why this
complexity was introduced for temporary addresses?  Why can't the client
can ask additional temporary addresses in a fresh IA?

BV> We do NOT want IA explosion. Ideally, a client should be able to use
the same IA forever under "normal" cases. A IA can have one or many
addresses, addresses will come and go. Server policy dictates the non-
temporary addresses assigned to a client. Client policy dictates the
temporary address needs - hence the client must have a way to say
"give me more". For example, if a client is running two applications that
each want unique temporary addresses, it has to request those from the
server. Later, when a third application starts, the client will need
another address.

- Can temporary  addresses and normal addresses can co-exist in same IA?
If yes, then, for renewal, does the client send normal  addresses  alone
in IA to the  server?  since,  the  renewal of  temporary  addresses  is

BV> YES the can both be in the SAME IA. That is the intention.

- I thought for decreasing the load of server, unlike DHCPv4, in DHCPv6,
the dns  updates  was moved to  client.  But, the draft  says  that, for
temporary addresses, the server has to update the DNS.  Why this feature
was included in server, instead of client?

BV> What we say in section 14 is:

   The server MAY update the DNS for a temporary address as described in
   section 4 of RFC3041, and MUST NOT update the DNS in any other way
   for a temporary address.

BV> This all depends how DDNS is handled with DHCPv6 and who is doing the
updates. We just wanted to be clear that if the server was doing DDNS
updates for the client, is must adhere to the requirements of RFC 3041
in doing them!!

-  Why  only  temporary  has  to be  updated  in  DNS?  why  not  normal

BV> See answer to previous question. DDNS updates are still TBD. Likely
the DHCPv4 FQDN option will be used (changing the A processing to reflect
AAAA processing and using the DUID for the client identification).

- I think for  updation,  we need to define,  hostname/FQDN  option  for

BV> Yes, we will need this.

- How can the client  specify  the number of address  it wants?  Will it
send IA optio with 'n' number empty of IA_ADDR option?  Instead of that,
can we define  another  option  OPT_RA  similar to OPT_RTA,  that can be
encapsulated in OPT_IA?

BV> The client can't specify how many non-temporary addresses it wants.
This is controlled by the server. The client *CAN* use multiple IAs and
if the server policy allows, that can easily be used to give the clients
LOTS of addresses (one set per IA).

- Section 17.1.2 says that the client collects  Advertise messages until
SOL_TIMEOUT has elapsed.  Then, RT will be  recalculated.  Now, does the
client needs to retransmit the SOLICIT  message?  If it is so, then, the
same server will reply multiple times.  But the retransmission algorithm
in Section 15 says that, it should retransmit the packet. 

BV> The client waits SOL_TIMEOUT but it does not retransmit the Solicit
if it has received at least one Advertise. Retransmit Solicit only if no
Advertise messages are received.

- In  section  17.1.2, we need to add a  sentence,  "When the RT reached
MRT, if the one or more valid advertise  message is obtained, the client
should stop sending Advertise message and proceed further with collected
Advertise  message".  Otherwise,  since MRC and MRD are 0, this  process
will go infinetly  according to algorithm specified in Section 15.  This
is also an implementation problem we faced.

BV> Haven't studied this issue.

- In some place, the server should fill "server-address" with one of its
address  based on the link in which the packet is  received.  In another
place, it is said that the  server-address  field can be filled with the
address configured by the administrator.  What is the standard procedure
to be followed?

BV> We probably should clean up the text to be consistent. I think the
answer is use configured address if so configured for that LINK, otherwise
use one of the LINK interface addresses.

- In Advertise,  should the server assign all the addresses asked by the
client?  (or) only few of them?

BV> It depends on the server's policies.

- Till what  time,  these  OFFERED  addresses  are  preserved  for those
clients to assign?

BV> My opinion is that the ADVERTISED addresses are just a possible set of
addresses the client will get and may not be the exact addresses. The client
must wait until the Reply to the Request before it knows which addresses it
got and before it does Duplicate Address Detection. The ADVERTISE should
include all of the parameters the client is likely to receive in the Reply,
but they are just possible values and not the actual values.

- If the server has fewer  addresses than the client has asked, will the
server assign fewer addresses or send AddrUnavail?

BV> I would only return AddrUnavail if NO addresses are available. If you
can assign some, give the client those. It can make a decisions as to 
whether it wants to accept them or not.

- The draft says that the renew  message can be used for checking up the
validity  of  the  other  configuration  parameters.  For  checking  the
validity  of them, will the client  send the option  codes in ORO option
(or) send the parameters in their respective options?

BV> The Renew message does not need to include those options (including
them in an ORO is probably a good idea so the server knows you want them).
It is really the Reply that matters and the server will Reply with the
current settings. The client can then apply those values. The server will
(I suspect) not really check them - it just Replies with the current

- Should release/decline of addresses be done for IA as whole?  (or) Can
few addresses be relased from an IA? (partial release)

BV> Individual addresses can be released or declined. The client MUST 
include the addresses to decline/release. The server ignores any addresses
that the client doesn't "own".

- Assuming the client is sending  multiple IAs for renewing,  the server
finds that one particular IA is not found in the client  bindings,  will
it renews the remaining IAs? (or) will it send NoBinding error?

BV> It can send a NoBinding status for that IA. (And renew the others.)

- What will the client do, for the multiple IAs sent for renew, only one
IA is missing in the reply?

BV> No sure what you asking? Is this a follow up to the previous question?
If the IA returns with a NoBinding status, the client may either continue
to use those addresses (since it must have gotten them from someone in the
past) or drop them (and the IA).

- Can you explain the differnce between, "configuration  information are
not valid" and "configuration information does not match".  In the first
case, for Confirm  message  ConfNoMatch is sent and for the next one, it
is  sending  SUCCESS.  The draft says that for  ConfNoMatch,  the client
should  send renew  message.  If the  configuration  parameters  are not
matching, then what is the use of sending renew message?

BV> Have to look into this one more.

- For the cases like, "conf parameters are not valid", "conf  parameters
does not match" and  "prefix  does not match",  what will the server do,
for the release message?  What will the server do? if (i) all, (ii) only
few  addresses  are invalid.  Will the server  release the address which
are valid?

BV> Have to look into this one more.

- Section says that, if the client is not able to validate the
authentication  for the REPLY  message,  then it should  start  with the
SOLICIT.  I feel that this is inefficient,  instead, it can try the next
available server which has sent the advertise message.

BV> Have to look into this one more.

- In the previous  versions, we have  Retransmission  Parameter  option.
Why it was removed?

BV> There are significant security / DOS issues with allowing the server
to set parameters. Also, there are issues as when these parameters are to
be used (vs the defaults). If a client moves to a completely different
DHCP domain, the parameters may not be valid and how does it know that?

- Some useful options were defined in DHCPv6 extension draft.  When will
those options be included in this draft?

BV> Suggest the ones you want to have included! Provide the text (if it
needs to be revised). That's what Ralph (as editor) has requested in the

I have found some typos in the draft.

- In section 7.3, for  reconfigure  message, the client should  intiate,
Renew/Reply not the Request/Reply

- In 19.2, it is  saying  that, for  Inform  message,  all the IAs to be
included.  This a simple cut-paste problem.

- 19.3.4 says, "The client uses the same  variables  and  retransmission
algorithm  as it does with  Rebind  or  Information....".  It  should be
"Renew or Information..."

- In 22.14, the server address field in Server Unicast Option is missing.

- In 22.19, User class option  message  format  looks messy,  because of
some sentences in between.



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