Re: [Softwires] I-D Action: draft-ietf-softwire-lw4over6-06.txt

[Ian Farrer <[e-mail]>]

HI Woj / Simon, 

Below is some proposed text around interface and prefix selection for tunnel creation.

@Simon, this changes some of the text that we previously agreed at WGLC, so please can you check it over?

Cheers,
Ian

> 
> Well, so the text from the above discussion does not appear in the draft. 
> What more however is that the text does not describe how a case of a WAN without a global IPv6 prefix is to be handled (is that also invalid - please state so in the draft). 
> Other cases: 
> - What is the WAN doesn't have a /64? 
> - What if there are multiple WAN interfaces?
> 
> If these are all invalid w/ lw46 - then please state so.
> 

[for Section 5.1]

For DHCPv6 based configuration of these parameters, the lwB4 SHOULD
implement OPTION_S46_CONT_LW as described in section 6.3 of
[I-D.ietf-softwire-map-dhcp].  This means that the lifetime of the
softwire and the derived configuration information (e.g. IPv4 shared
address, IPv4 address) is bound to the lifetime of the DHCPv6 lease.
If stateful IPv4 configuration or additional IPv4 configuration
information is required, DHCPv4 [RFC2131] must be used.

The received DHCPv6 lw4o6 configuration is applicable only to the interface
from which the DHCP Solicit message was sourced. Although it would be possible to
extend lw4o6 to have more than one active WAN interface and corresponding 
lw4o6 tunnels configured simultaneously, this document is only concerned with 
the use of a single interface and tunnel.

On receipt of OPTION_S46_CONT_LW, the lwB4 performs a longest prefix match 
between the IPv6 address of the lwAFTR (contained in OPTION_S46_BR) and the 
configured prefixes on the interface that originated the DHCP solicit message.
If the longest prefix match returns more than one matching prefix, then an
implementation specific tie-breaker MUST be performed to return a single prefix.
If no matching prefix of the same IPv6 scope (as described by [RFC4007]), then
the lwB4 MUST NOT attempt to configure the softwire tunnel interface. 

If a change in the interface addressing occurs, then the tunnel interface 
configuration process MUST be restarted.

The result forms the subnet to be used for sourcing the lw4o6 tunnel. The full
/128 prefix is then constructed in the same manner as [I-D.ietf-softwire-map].