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List:       ipng
Subject:    (IPng 2647) hlim and IF on API
From:       Kazuhiko Yamamoto =?ISO-2022-JP?B?GyRCOzNLXE9CSScbKEI=?=  <kazu () is ! aist-nara ! ac ! 
Date:       1996-12-23 10:19:59
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Hi,

I have several questions and suggestions concerned with hop-limit and
IF selection.

(1) Hop Limit

IPV6_UNICAST_HOPS and IPV6_MULTICAST_HOPS are defined on the basic API 
draft. Are there any strong reasons to separate them?

NDP and RIPng requires to set hop-limit 255. But I believe that it is
very good idea to set hop-limit 255 for all on-link communication. Are 
there any problem if the basic IPv6 spec requires it?

(2) IF

The basic API draft defines IPV6_MULTICAST_IF whereas the advanced API
makes it possible to select an IF with sendmsg(). If they
conflicts(e.g. select IF_1 with setsockopt() then sendmsg() to IF_2),
how should it work? Moreover, if the SO_DONTROUTE option is specified,
what will happen?

sendmsg() successes only when the destination is link-local-used
address or multicast. That is, sendmsg() fails if the destination is
off-link since a gateway can't be resolved. This explanation should be
contained in the advanced API spec.

<My suggestions>

(1) Hop Limit

Delete IPV6_UNICAST_HOPS and IPV6_MULTICAST_HOPS. Then define
IPV6_HOPS which can be used for both unicast and multicast.

Require 255 hop-limit if the destination starts with 0xfe80 and
0xff02.

(2) IF

Delete IPV6_MULTICAST_IF and SO_DONTROUTE. For interface selection,
use sendmsg(). If the destination is not link-local-use address nor
multicast, sendmsg() returns an error.


Comments?

--Kazu
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