Subject: Re: IPv6_UNICAST_HOPS and IPV6_HOPLIMT

From: "Lori Napoli" <[email-masked]>
Date: Sun, 10 Jun 2001 15:11:35 -0400

I should have been more specific with my question.  I agree the ancillary
data will override the setsockopt.  I was really asking what happens if an
application does a setsockopt for IPV6_UNICAST_HOPS and IPV6_HOPLIMIT?
Does the IPV6_HOPLIMIT replace the value specified by the IPV6_UNICAST_HOPS
or are they separate values?   Lets say IPV6_UNICAST_HOPS = x, kernel
default = z and IPV6_HOPLIMIT = y.    Would 'y' be the hoplimit used for a
unicast send?  Then suppose the application clears the IPV6_HOPLIMIT value.
Do we fall back to 'x' (the value specified on IPV6_UNICAST_HOPS) or 'z'
(kernel default)?

Thanks
Lori

>>>>> On Tue, 5 Jun 2001 12:45:31 -0400,
>>>>> "Lori Napoli" <[email-masked]> said:

> Can someone explain how the two options IPv6_UNICAST_HOPS and
IPv6_HOPLIMIT
> work together.  Does IPv6_UNICAST_HOPS override IPV6_HOPLIMIT ?  And
> IPv6_HOPLIMIT overrides the system configured default?

IPV6_HOPLIMIT overrides both IPV6_UNICAST_HOPS and the system
configured default.

6.3.  Specifying/Receiving the Hop Limit

   The outgoing hop limit is normally specified with either the
   IPV6_UNICAST_HOPS socket option or the IPV6_MULTICAST_HOPS socket
   option, both of which are described in [RFC-2553].  Specifying the
   hop limit as ancillary data lets the application override either the
   kernel's default or a previously specified value, for either a
   unicast destination or a multicast destination, for a single output
   operation.
(draft-ietf-ipngwg-rfc2292bis-02.txt, which has already expired...)

                         JINMEI, Tatuya
                         Communication Platform Lab.
                         Corporate R&D Center, Toshiba Corp.
                         [email-masked]

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From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Mon, 25 Jun 2001 18:15:18 +0900

>>>>> On Sun, 10 Jun 2001 15:11:35 -0400, 

> or are they separate values?

Sorry, I forgot to reply to this.  I believe the spec is ambiguous on
this point.  Our (KAME's) implementation always prefer IPV6_HOPLIMIT
to IPV6_xxCAST_HOPS.  So,

> Lets say IPV6_UNICAST_HOPS = x, kernel
> unicast send?

Yes, in our implementation.

> Then suppose the application clears the IPV6_HOPLIMIT value.

Our implementation should fall back to 'x'.

It would be better to make this clear on the next revision of the
rfc2292bis draft.

					JINMEI, Tatuya