How to turn off IPV6 (link local)

[Bernd Eckenfels]

Hello,

I started that discussion on linux-kernel, but I think it is better here:

The problem is, that it is not possible to up an ipv4 interface completely
without an ipv6 address (as long as the kernel is ipv6 enabled)

The ip-sysctl help tells me that it should be possible to use "autoconf" to
avoid the link local (and loopback?) address, and accept_ra to avoid
stateless autoconfigured router prefix announcements:

# accept_ra - BOOLEAN
#         Accept Router Advertisements; autoconfigure using them.
#
#         Functional default: enabled if local forwarding is disabled.
#                             disabled if local forwarding is enabled.
...
# autoconf - BOOLEAN
#         Configure link-local addresses using L2 hardware addresses.
# 
#         Default: TRUE

However this is not correct, autoconf does only affect the same addresses as
accept_ra does, i.e. the one announces (global and site local).

So I think autoconf=0 should avoid  adding the fe80:: link local  address (as
well as lo ::1), as documented.


There are application problems, if the interface has (only) the link local
prefix or corrupt global prefixes.

If the application prefers ipv6 it will try to use them, and only on connect
it receives an error. Some do then ipv4 fallback (lynx) some dont (mozilla).

So qestions:

- is the kernel interpretation auf autoconf=0 or the documntation right?

- how should an application avoid connecting via an interface which has 
  only addresses for the wrong scope?

- is falling back from v6 to v4 on connect errors somehwere recommended/described?


I can prepare a kernel patch to make autoconf stop configuring any ipv6
address on upping an interface.

Some of the discussion is archived on the debian bugtracker:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=253590

Greetings
Bernd
-- 
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